Audio Component Interconnection - Pro

Transcription

Installation Knowledge and Techniques
Audio Component Interconnection
OBJECTIVES
Describe the different connector types used in an audio system.
Discuss the signal path for Audio Component Interconnection.
Discuss the different wiring configurations used for speaker connection with an audio amplifier.
INTRODUCTION
Interconnecting different brands of mobile audio products can have many variations that affect the way
the products perform. Even mobile audio products within the same brand may not necessarily just “plug and
play” together. For any system to perform correctly, mobile audio products must be connected according to the
flow of the ‘signal path’. This means that the signal must pass through the various components in the best order
necessary to achieve the desired effect. Mobile audio products that are connected outside of the signal path
or incorrectly connected within the signal path will either have no effect or will have a negative effect on the
overall sound quality outcome. Additionally, incorrect placement within the signal path may duplicate or bypass
some very important functions which can lead to damaged electronics and speakers.
Signal Path
Signal Cables and Connections
“Audio Interconnects” allow the signal to pass from one audio component into another. Proper audio
interconnect cables should be used to reduce the chance of noise and impaired sound quality.
Preamp Level Audio Signal
Most audio interconnect cables are technically deemed preamp level audio cables. Preamp denotes the
signal characteristics BEFORE the amplifier(s) in the audio system. Preamp level audio cables must have a
minimum of two conductors present for each channel connected. Each channel must have a (+) positive and (-)
signal conductor present in the cable. The training module “Introduction to AC and Waveforms” explains why
two conductors are needed for audio circuits, both before and after the amplifier(s). If you need more information about the fundamentals of AC, waveforms, and the content of an audio signal, please refer to the Introduction to AC and Waveforms training module.
Audio Interconnect Cable Construction
Negative Conductor
Many variations of the two conductor cable are used for
the purpose of preamp level audio interconnection. From flat (side
by side) conductors to coaxial conductors (one wrapped around
the other running on the same axis), and even intertwined conducInsulator
tors (known as “twisted pairs”) are found throughout both mobile
and residential audio systems. Professional audio systems, such
Positive Conductor
as those installed in concert halls, sports arenas, and other large
A cross sectional view of 2 conductor “covenues almost always use a balanced signal transfer method that
axial” interconnect cable.
use twisted and shielded 3 conductor audio interconnects.
Insulator
All contents copyrighted © 2010 Seven Wanders LLC. All rights reserved
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A close-up of twisted audio cables
Twisted audio cables shown with RCA ends
Noise and Interference in Audio Cables
Nearly all types of audio signal transfer, where the signal leaves one component and uses interconnecting cables to another component, have the potential for interference, more commonly called “noise”, can easily
become an unwelcome part of the audio signal. Coaxial preamp level cables using a wound shield instead of a
braided shield can experience noise problems quite easily. Cables that have a secondary shield or drain may offer better noise rejection capability. Twisted pair audio interconnection cables offer the highest amount of noise
rejection in a vehicle environment when an analog audio output is utilized.
With any type of signal cable, all of the shielding in the world will not reject the relatively low frequency noises that electromagnetically induced into a cable. This most often surfaces as “engine noise” when a
car audio system is affected with noise. Engine noise is an audible whine that varies in pitch with engine speed.
As the RPM’s of the increase, so will the noise. Although the type of cable used may not be the cause of the
noise, it may be the victim to noises once a problem surfaces. Fundamentally, when current travels through a
conductor, there is a surrounding magnetic field. When there is a large amount of current, there is a large surrounding magnetic field. When a relatively low level audio signal conductor comes within the range of a high
current magnetic field, the magnetism can be picked up as if the audio cable were an antenna for the noise. This
is called inductive coupling. This is also the major reason why both MECP and many veteran installers always
warn installers to run power wiring separate from preamp level audio signal cable wiring.
According to the MECP Basic Installer Study Guide, preamp level audio cables and power cables
should be run a minimum of 18 inches apart and, if they cross at all, it’s best that they cross at 90 degrees.
MECP also makes a general recommendation that, where possible, run the preamp level audio cables down the
opposite side of the vehicle from the power cables. While this is a good general reference, the amount of current
flowing in the power wire as well as the voltage level of the preamp level audio signal are factors to consider.
With ideal conditions (low current power wire and high voltage audio signal), audible interference may never be
an issue.
The RCA Connector on Audio Interconnects
Signal (+)
Signal Reference Ground
A Typical RCA type Connector
The majority of car audio components use signal input connections that are called RCA connectors. These are a standardized
connector made popular early in the days of audio by, guess who,
a company called RCA. The connector is by far the most common
type of audio connector on both mobile audio components and mobile audio signal cables.
Residential audio components also feature RCA connectors on their ANALOG outputs, COMPOSITE VIDEO,
or COAXIAL DIGITAL outputs. Although each signal
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type passing through the cable is different, the standardized
connector makes the manufacture of cables and audio components much easier. Frequently, audio signal cables
that transfer signal (namely music) from one device to another are simply referred to “RCA Cables”. That is a
description of both the cable (being audio cable) and the connector it is terminated with, the RCA terminal.
Although there are still many other types of connectors used in a car audio system, most are proprietary
(or unique) to the particular brand of equipment. This is part of the reason that one aftermarket brand of headunit may not plug into a different aftermarket brand of CD changer.
Center Pin Conductor
Outer or "Shield" Conductor
Inside View of an RCA type Connector
Any signal connectors that are loose or mismatched can contribute to noise and static. High performance
equipment is most susceptible to noises that can be easily recognized due to the extreme clarity of the audio signal and equivalent quality interconnects should be used. Conversely, low quality audio equipment is more prone
to simply having noise problems and, truthfully, better audio interconnects can’t fix it.
Headunits
Headunit Output Types
Various styles of headunits require different interconnection procedures with other downstream components based on the output circuitry contained in the unit and the customer preferences. It’s important to identify
the type of headunit that will be the foundation of an entirely new mobile audio system. It is also very important
to identify the type of headunit prior to connecting it into an existing audio system (such as an OEM upgrade) in
the event it is not directly compatible.
Additionally, identification of a headunit type prior to a complete system installation may outline any
concerns that need to be addressed with additional installation labor or with some form of electronic interface,
cable assembly, wiring harness, or other adapter.
Preamp Only Units
The term preamp means “before the amplifier”. Preamp head units are the lowest in distortion and highest in fidelity and require a separate amplifier to function. These units are also the highest priced of a particular
brand lineup due to the high grade of internal components.
Signal to noise ratios are typically the highest in these units,
indicating high dynamic range and little or no hiss. Preamp
units will not directly drive a speaker without the addition of
an amplifier. These units are typically the building block of a
multi-component car audio system.
While most preamp units have RCA connectors on
the preamp level audio output, there can technically be other
possible connector types. As mobile audio components feature
more complex ways to move signal from one device to anoth3
er, connector types will also reflect the change in technologies.
Your Introduction to Mobile Electronics Equipment workbook discusses headunits and the “format”
types, this workbook will highlight the “output” type of the headunit. The importance of the output type is an
element of concern if all of the components are to work in harmony to produce good mobile audio.
Analog Audio Preamp Outputs
Analog audio outputs exist on nearly every preamp level headunit available in the market. Analog preamp level audio outputs are an exact representation of the original audio signal. Simply put, the analog signal
(eventually) transfers into the amplifier and, because it is an exact representation of the original audio signal,
it is simply amplified to provide a more powerful electrical energy that will drive speakers. An analog preamp
level output won’t directly drive a speaker on it’s own.
The bulk of mobile audio components that feature preamp level analog audio outputs do so as RCA
jacks on the back of the headunit. As long as the next component in the signal chain has an analog RCA input
(one each for left channel and right channel), the two components simply plug together. The RED RCA jack
always denotes the Right Channel. The other color, typically White or Black, denotes the Left Channel. That’s
the way it’s always been done. “Red for Right”.
Single Ended or Balanced Output?
Nearly all mobile audio products use a single ended audio output. This is especially noticed by the end
connector and the number of conductors it contains. Typical RCA connectors have only two conductors and,
therefore, are considered single ended.
Normal Signal Input
(+)
Signal Reference to Ground
Analog Signal Content
(Non Inverting)
Operational Amplifier
Single Ended Audio Output
Single Ended Audio Output Stage
A single ended audio output uses one conductor for the signal (+) and another, separate conductor for the
signal reference ground. The signal reference ground may also function as the shield or outermost layer of the
cable. Many multiple layer cables have more than one shield that surround the signal (+) and signal ground, but
there are still only two conductors of signal within that audio output and interconnect cable. A single ended output is simply fed into an operational amplifier (op-amp) which increases the signal level to a maximum amount
of signal voltage which will then be “amplified” by an amplifier. If there are any noises present on the signal
before the op-amp, the output carries the noise right along, only equally as amplified as the signal. This is why
keeping RCA interconnect cables away from other noise sources is so important.
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Balanced outputs, on the other hand, use three conductors. The main difference is that a balanced audio output uses one conductor for the signal (+) and another, separate conductor for an inverted signal exactly
opposite of the signal (+) which is typically called the signal (-). The third conductor is for the signal reference
ground. The key element is that there are two signals transmitted that are exact opposites of each other. Once the
signals are fed into a differential amplifier stage, the differential amplifier amplifies only the “difference” of the
signal. This effectively cancels out any noises imposed on the two signal conductors because the noise will be
“common” (meaning NOT different) to each conductor. Since the differential amplifier only amplifies the different signals, the common signal of any noises is basically rejected. This is known as common-mode rejection.
The majority of products using balanced line audio transmission are professional grade audio components for high dollar residential or studio applications. Typical applications such as these use an XLR connector
rather than an RCA type connector.
(Non Inverting)
Normal Signal Input
(+)
Signal Reference to Ground
(-)
Inverting Signal Input
(Inverted)
Differential Amplifier
Balanced Audio Output
True Balanced Audio Output Stage
There have been products built for mobile audio applications that convert a single ended output from a
headunit to a balanced line. These require a transmitter and a receiver between the single ended headunit and the
device receiving the signal. This receiver can be built into an amplifier or exist as a stand alone external device.
Headunits, for the most part, do not feature balanced outputs. Several years ago in the mid 1990’s, Rockford
Fosgate built a competition headunit (Model #RFX-8140) capable of balanced line outputs that, when used in
that configuration, created 17 volts peak to peak output voltage at full volume. This was awesome, but way too
much signal for most down stream components to handle. The key to mobile audio signal transfer is that a true
balanced connection doesn’t use an RCA connector, but something that has at least 3 conductors.
Some upper end mobile audio components treat the input of a single ended signal as “quasi balanced”
attempting to reject the noise present on the signal (+) and signal reference ground at the RCA input of the component itself. While this produces better noise rejection than a straight single ended audio input, it isn’t a true
balanced audio signal as it wasn’t transmitted as such.
Output Type Different than Format Type
An analog source format headunit (such as a cassette tape player) can ONLY have an analog audio
output (for cost reasons more than anything else), because the material played is recorded in an analog format.
A digital format headunit (such as a CD player) can have an analog output, a digital output, or both.
In order for a digital format headunit to have an analog audio output, the headunit must have a built in
D/A (digital-to-analog) converter. The D/A converter allows the headunit to use common analog components to process and amplify the audio signal.
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Analog Output Specifications
High end analog audio output models within a brand that qualify as RCA preamp only (no direct speaker
outputs) typically offer serious “system building block” features such as:
High Voltage, Low Source Impedance RCA Preouts
1. Higher Voltage is generally better. More than 2 volts is good, over 4 volts is great. It’s important for
the output to be undistorted (unclipped) up to full volume.
2. Lower Source Impedance is better. Less than 300 ohms is good, less than 100 ohms is great. The
source impedance is also called “output impedance”.
High Signal to Noise Ratio (S/N Ratio)
1. Higher is better. In the 90dB range is good, over 100dB is great. Better than 110dB is fabulous. Signal to noise is simply a ratio of the audio signal versus the “noise” of the operational characteristic
within the headunit (or other component).
Subwoofer Output
1. A dedicated RCA subwoofer output with it’s own level control is very useful in making minor
adjustments that are needed when, for example, switching between FM radio and CD sources, or
simply between different types of music.
Front and Rear Outputs
1. A selection of Full Range or High Pass Front and Rear RCA outputs allow the headunit to both control and route the signal to the appropriate components down stream.
Additional features may be part of the headunit, but the features listed are exclusive to the preamp section of the headunit where the output must connect to another device (eventually an amplifier and speaker) to
hear sound. The more of these features contained in a preamp section of a headunit, the better system building
block it becomes.
Digital Audio Preamp Outputs
Digital audio outputs are found only on digital source format headunits. This is done primarily for cost
reasons as the price of analog sources simply don’t support the conversion into digital audio where there would
be little, if any, audible benefit. It should be noted that there are relatively few mobile audio headunits that currently feature a digital audio output. Many home and professional audio products feature digital audio outputs
on source formats that are digital. This is where most digital connections occur.
Digital audio signals are actually a bunch of uniquely coded “bits” of ones and zeros that contain the
code for an audio signal. More bits mean a higher resolution. Compact Discs use 16 bits of information. The
Compact Disc format was co-invented by Sony and Philips back in 1982. Since then, the two companies have
worked to standardize the way digital audio passes into and out of all consumer devices. The result, regardless
of the connector and cable style used, is the S/PDIF digital signal (Sony/Philips Digital Interface Format). Each
type of connector and cable type may carry the digital signal differently, but the format each audio
component recognizes is based on a S/PDIF standard format. The standardized digital output voltage
levels of S/PDIF consumer products is 0.5 volts.
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There are four basic types of plug or connector style in digital audio outputs. Of those four plug
styles, two are used on optical cables (plastic or glass-fiber) while the remaining two are used on electrical (copper or silver) cables.
Coaxial Digital Connections
The coaxial digital connection uses a very familiar RCA connector, but a more
refined coaxial cable to transmit digital audio between components. The high quality of
the cable is necessary to promote an accurate conversion from a digital signal to an analog signal. The cable is rated at 75 ohms (+/-5%) to ensure accuracy of the audio signal
reproduction. A coaxial digital connection is said to have a higher maximum bandwidth
(capacity for information) than the optical type connections.
Also different from the Analog RCA connections is the fact that digital audio can
transmit multiple channels of audio on a single cable. This means that a coaxial digital
output, be it one, two, or more channels, only requires one single RCA connection and
coaxial digital cable assembly. Most car audio components do not feature coaxial digital
audio connections at this time.
TosLink Digital Connections
The TosLink connector type was made standard by the Toshiba Corporation and is an affordable alternative to coaxial digital audio connections. The cable that the TosLink connector mates to is a optical cable that
transmits light pulses as ones and zeros, rather than electrical pulses as in the coaxial cable. The outstanding
benefit is that surrounding sources of noise have little or no effect on the light pulse
and, when compared to an electrical pulse, the light pulse transmits no interference
to surrounding devices.
What makes the overall combination of the TosLink connector and the
optical cable affordable is that the majority of cables employ a flexible plastic as
opposed to a more expensive glass-fiber type of cable.
The TosLink digital audio output is found on many mobile DVD players
that feature Dolby Digital and DTS encoded audio material. The TosLink digital
connection is most ideal for it’s noise immunity in the environment of the vehicle,
but when used it requires a processor with a digital input to function with the commercially available car audio amplifiers offered at Best Buy stores. The TosLink
TosLink Optical Connection
connection is widely used in consumer home audio products offered at most Best
Buy stores.
AES/EBU Digital Connections
This is a professional grade version of S/PDIF digital audio data transmission found primarily on only the most expensive home and professional audio
equipment. The AES/EBU interface uses a balanced line 3 conductor cable (digital
signal +, digital signal - or “inverted”, and ground) and a pro-audio style XLR 3 pin
locking connector. Perhaps the biggest single advantage of the AES/EBU digital audio output is that it’s transmitted at 5 volts as opposed to the standard S/PDIF levels
of 0.5 volts. Being 5 volts as well as balanced line makes it very difficult for noise,
cable length, and outside interference to be an issue with large audio systems. The
AES/EBU digital audio interface is, at this time, not found on any mobile headunits,
nor is it found on mobile audio amplifiers or signal processors.
Anything that features an AES/EBU digital audio output must plug into a
device with an AES/EBU input for the AES/EBU digital audio format to work. AES XLR 3-pin Connector
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represents the Audio Engineering Society, an association of professionals in the business of sound reproduction
of all types. EBU represents the European Broadcast Society, a similar organization in Europe. Both organizations helped to develop this digital audio standard which one could consider S/PDIF “kicked up a notch”.
ST-Type Digital Connections
The ST -Type of optical interface uses more expensive glass fiber optical cable as well as a proprietary
locking connector which differs from the TosLink style of connector. It was originally developed by AT&T for
use within the telecommunications industry and was easily adapted to digital audio applications. Like the AES/
EBU interface, the ST-Type is not found in any mobile audio products.
Speaker Outputs
Headunits which contain an audio output that is meant to directly drive a speaker are referred to as units
with “internal power” or “deck power”.
Low Power Units
Low power decks usually exhibit the highest distortion. These units appear to be a good value for their
price but should be reconsidered when the customer wishes to use a separate amplifier or considers the headunit
as a building block for a larger car audio system investment.
Many amplifiers in the lower end on a brand lineup will accept direct connection from the speaker leads
of low power (and sometimes high power) head units.
Low power headunits are generally common ground units. Common ground means that the electrical
(chassis) ground of the unit is the same as the audio ground (or speaker negative). Although a common ground
headunit may have several different wires for each speaker (-) and a chassis ground, electrically they can all be
traced to a “common” point, hence the name common ground.
Some older 1970’s Fords, Chryslers, Mercedes-Benz, and Volkswagens used a common ground headunit
as factory equipment. In these vehicles, only one speaker wire went to each speaker. The second wire, typically the speaker (-), was simply grounded to the body of the vehicle. The conductive chassis of the car was the
“wire” that connected the speaker to the same common ground point as the headunit.
Very few common ground headunits actually exist today. All but the most inexpensive headunits are now
considered high power units using a different audio grounding scheme. The two major reasons common ground
radios have really become outdated is the lack of immunity to engine noise and the limitations of built-in power
to drive speakers.
High-Power Units
High power decks are either low power units with built in power boosters or can be true high power devices using better fidelity designs. Almost all high power units use a technique called “floating ground” which
requires careful attention to hookup. In a floating ground configuration, the speaker leads use a separate negative (-) output for each channel and they are NOT COMMON to the chassis ground. High power headunits are,
by definition, likely to be floating ground units because the overall output of a floating design has much more
output than that of a common ground design. Most headunits within the Best Buy Mobile Electronics Department are of the floating ground style.
Only amplifiers made to accept a floating ground unit directly may be used without a special adapter.
Some amplifiers have high level inputs that can directly accept a floating ground input. These high
level inputs can accept speaker level signals, provided the output type is the right type. In other words,
you can’t connect a floating ground output to a common ground high level amplifier input.
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On all high power floating ground headunits, connections must be made directly to the indiAll contents copyrighted © 2010 Seven Wanders LLC. All rights reserved
vidual speaker without the positive or negative lead connecting to ground. NEVER connect any floating ground
speaker outputs to the chassis of the vehicle.
Signal Processors
The “In-Between” Component
Active signal processing in a mobile audio system can have many possibilities, but the basic interconnection remains nearly the same. The active signal processor(s) simply fit in line between the headunit output
and the amplifier(s) input(s). The active signal processor simply takes signal in, does something to it, and outputs it to the next component.
What does the processor actually do? Processors can perform many system enhancement functions.
Equalizers, crossovers, bass boost devices, center channel processors, and Dolby Digital decoders are all forms
of signal processors.
This is the very simple explanation a signal processor. What about when it comes down to a particular
type of processor or connecting several signal processors? This training manual will address two of the most
frequently used signal processors in mobile audio systems These are equalizers and crossovers.
Fundamentally, besides doing something to the signal that passes through it, a signal processor often has
the equally important function of a “pre-amplifier” or pre-amp. The purpose a pre-amp serves is take the workload of directly driving amplifiers away from the headunit, and instead, put some of the workload on the signal
processor. This means, for example, that a signal processor that has a pre-amp function may be able to take a
low headunit output voltage and increase the voltage output when it “drives” the amplifier input.
It is extremely important to consider the single most important factor when adding a signal processor into an audio system. A signal processor is not meant to fix a poorly designed system, it’s meant
to enhance a well designed system.
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Equalizers
Analog Equalizer
This section describes analog input RCA equalizers. These EQ’s
come in many shapes and sizes and include those with knobs, slide conL R
trols, or even digital displays. Do not confuse the input type with the
“product description”. Many so called “Digital EQ’s that do the processing of signal in the digital domain do so after an analog to digital (A/D)
conversion. Once the signal processing has been applied, the signal goes
back through a digital to analog (D/A) conversion. This section will deal
with EQ’s that have an analog input and output. The method of processing
inside the EQ has very little to do with the installer.
The connection of audio signal into an analog equalizer built for
use in a mobile is generally just two channels, one left and one right. The
signal input type is typically through a pair of RCA jacks. Once the signal
L R
has been fed into the equalizer, the signal is processed by whatever equalFrom
Head Unit
ization style the component features. Graphic or Parametric equalization
RCA Inputs
is typical. Finally, the signal outputs carry the same two channels on to the
next component in the signal chain. The audio output from the equalizer is identical to the input with the addition of the equalization effects in the signal.
RCA Outputs
To
Amplifier(s)
or Crossover
Digital Equalizer/Processor/Decoder
A true digital equalizer for use in mobile audio applications is a whole different machine. While the
digital processing function may be part of an analog input/output EQ, the true digital EQ accepts a direct digital
input. Once the audio signal is in the digital domain, it isn’t limited to two channels of sound.
Many of the examples of digital equalizers for mobile audio with a digital input are actually much more
than just an equalizer. While it’s not an absolute assumption that every digital EQ has more functions on board,
the power and flexibility of processing audio signal in the digital domain allows the addition of many other signal processing chores without large increases in product costs. Typically, digital EQ’s offer multi-channel audio
decoding, digital soundfield processing, channel specific frequency filtering (a fancy name for a crossover), and
other signal “routing” functions that determine which portion of the signal goes to which output. There are many
forms a digital EQ can take on, including the flexibility of having the option of either RCA input OR a digital
input such as the Sony Digital EQ pictured below.
In mobile audio/video “surround sound” systems, perhaps the most likely place to find a true digital
input signal processor, the digital equalization most likely
is part of a “decoder” specifically designed to decode Dolby
Digital and DTS bitstreams. This allows one single digital signal connection (typically a TosLink optical cable) to
send as many as six discrete (individual) channels of signal
into the digital decoder. These six channels are the same
six channels often used in home theater systems, which are
known as 5.1 channels of sound.
The “5” represents five full range channels (Front
Left, Center, and Front Right, plus Rear Left and Right),
TosLink Digital Inputs
then a sixth channel called an LFE channel (Low Frequency
Multiple Discrete Outputs
Effects) which is limited in bandwidth to only low frequencies designated to drive a subwoofer output. To gain access
Analog RCA Inputs
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to these encoded layers of sound, they need to either travel
over discrete connections from the source unit to a processor (which would mean six RCA’s) or easily over a
digital connection as individual codes on a single line which are then “decoded” by the digital processor. This
digital output is available, for example, on mobile audio headunits that feature playback of DVD-Video or
DVD-Audio software.
To give an example that very closely mirrors the connection scheme, think of a home audio DVD player
and a receiver capable of decoding Dolby Digital and DTS information. Anyone who has ever connected these
components in a home audio environment knows that there are a couple of options with regard to audio input/
output connections. Most of these components feature standard RCA jacks to go the analog route, but limit the
audio information to the standard two channels of information, left channel and right channel. The other, more
exciting option involves the connection of the digital audio output between the DVD player and the digital
audio input on the receiver so that the receiver can decode and process the 5.1 channels of information to the
discrete (individual) outputs.
Whatever the architecture of the digital EQ, nearly all of the mobile audio products that feature digital
inputs will have an analog RCA output. How many outputs depends on how many channels of information the
digital signal contains. This is typically between two and six discrete (individual) outputs. The reason for this is
that nearly every car audio amplifier has, you guessed it, RCA audio inputs. A digital output wouldn’t do much
good if it couldn’t connect into anything.
Active Crossovers
Active crossovers are named as such because they actively (that is, electronically) alter the signal to
either pass or block a particular range of frequencies. The basic architecture of a crossover takes an input and
then separates the range of frequencies into specific outputs that connect to amplifier channels driving speakers
which match that range of frequency content.
Active crossovers are defined by the number of outputs or “ways” that the full range audio signal is split
up.
Two-Way Active Crossovers
Most active crossovers start with two outputs, or two “ways” to split up the audio signal. A two way
crossover consists of two basic outputs; one High Pass and the other a Low Pass. On the high pass output, beyond the cut-off frequency (called the crossover point), only the higher frequencies will pass. Frequencies lower
than the crossover point will be blocked in a high pass output. Conversely, a low pass output allows the frequencies below the crossover point to pass and blocks out the frequencies above that point.
Crossover Frequency
dB
High Pass Section
Low Pass Section
20 Hz
Frequency
20, 000 Hz
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A good way to think of the high pass and low pass relationship is to think of a four lane highway where
either direction has two lanes or “ways”. Some cars travel faster than others and to adequately manage the flow
of traffic between those two lanes, it would make sense to put high speed cars in the high speed lane and low
speed cars in the low speed lane. Just what determines whether a vehicle is high or low speed is that “cutoff”
or crossover point. Once each vehicle is directed into a lane that can deal with it’s speed properly, traffic flows
most efficiently. Audio is the same way in that the full range of frequencies has low frequencies and high frequencies. Not all of those frequencies work well in the same “lane” together. Think of the lane as a speaker. The
high frequency lane represented by a tweeter won’t do well if there is a lot of low frequency “traffic” in the high
frequency lane. Eventually, there will be a crash. In the real world of mobile audio, that crash is blown or damaged speakers. The same goes for midrange drivers and subwoofers, as each prefers a certain range of frequencies, but not the entire spectrum.
A simple two-way active
crossover with one (symmetrical) crossover point
R
L
High Pass
From Head
Unit or
Equalizer
L
R
Freq
To Amplifiers
Input
0
X10
Low Pass
R
L
The standard two way crossover uses a single pair of RCA inputs (one left and one right) then splits
those to two distinct outputs. Depending on the type of frequency control, the crossover point may have one
adjustment or two. A single adjustment denotes a crossover point that is the SAME for both the high pass and
low pass outputs. The only difference is simply the signal that passes or is blocked from that point, which is
determined by a high pass or low pass configuration. These are known as symmetrical crossover points. Two
separate adjustments simply mean that the high pass crossover point can be different than the low pass crossover point. Two separate crossover points are known as non-symmetrical or asymmetrical crossover points.
Having asymmetrical crossover points typically makes a crossover more expensive, but adds a lot of
flexibility to the overall tuning of a mobile audio system. After all, who says that just because the low pass
crossover point is ideal at a certain frequency that the high pass will be ideal in the exact same place?
Three-Way Active Crossovers
Building on the idea of what is contained in a two-way active crossover, The standard three-way active
crossover uses a single pair of RCA inputs (one left and one right) then splits those to three distinct outputs.
Rather than just a high pass and a low pass, there’s an additional one called the band pass output. The band pass
output has a band of frequencies that pass through, but rejects (or blocks) frequencies which are below
the range, and above the range of that bandwidth. The range of frequency within that bandwidth is
known as the pass band (short for “bandwidth that passes”). This is how the term band pass crossover
came about. The band pass crossover essentially has BOTH high pass and low pass elements in combi12
nation.
Typical Band Pass Frequency Range
dB
20 Hz
Frequency
20, 000 Hz
Most band pass applications involve using the output of the crossover to directly drive amplifier channels that will power a dedicated midrange or “midbass” driver. This is a driver that is exclusively dedicated to
the range of frequencies within the pass band. Frequencies above and below the pass band are handled by different speakers (and amplifier channels).
As active crossovers become more complex and feature more outputs, it becomes necessary to supply a
dedicated set of amplifier channels to make use of each output range. Recall the two way active crossover was
similar to two lanes of traffic, one moving slow and the other moving fast. In a three way active crossover, there
is now a third lane of audio “traffic”. Think of them as fast, medium, and slow moving lanes.
If slow traffic were considered to be anything below 50mph, then we could say the cut off point between
slow and medium speeds is 50mph. Below 50mph is slow lane traffic, above 50mph is medium speed traffic. Now for the break between the next lane, medium speed to fast. Say that break point is 100mph. Anything
below 100mph, but above 50mph, is considered medium speed while traffic above 100 is considered fast lane
traffic. The medium speed lane now becomes between 50-100mph, or the pass band is 50-100mph.
Band Pass to High Pass
Crossover Frequency
Low Pass to Band Pass
Crossover Frequency
dB
Low Pass Section
20 Hz
Band Pass Section
Frequency
High Pass Section
20, 000 Hz
With audio, instead of miles per hour, it’s frequency that decides the “lane” or output of the particular audio signal. Generally, very low frequencies (below 20Hz) and very high frequencies (above
20,000Hz) are allowed to “roll off” naturally. Rolling off means that there is no sense to further filter
the signal going to the amplifier or speaker because the speaker can not reproduce these signals. With
13
frequencies within a band pass response however, the speaker can still effectively play into certain ranges that
are not desired, so an active crossover with a band pass output is required. These are the circumstances under
which most three-way active crossovers are installed. As with a two-way crossover, the three-way crossover can
also have symmetrical or asymmetrical crossover points. Typically, the more expensive and complex three-way
active crossovers offer asymmetrical crossover points, whereas more basic versions have fixed points where one
output stops and the next one begins.
A simple three-way active crossover with two
(symmetrical) crossover
points
High Pass
R
L
Band Pass
R
L
Low Pass
R
L
Freq
From Head
Unit or
Equalizer
L
R
Input
Freq
To Amplifiers
Beyond three way active crossovers, there are occasionally four and five way crossovers, but it is rare to
see these in a car audio application due to the necessity of multiple dedicated amplifier channels as well as the
complexity of choosing and tuning the crossover points on each individual amplifier channel and speaker.
Subsonic Filtering
There is yet another crossover which technically has a band pass response. When a crossover has a
“subsonic” or “infrasonic” filter for the subwoofer, it can filter out extremely low frequencies that the subwoofer
can’t reproduce. While many subwoofers can move at frequencies below 20Hz, they are below human hearing range and are a waste of amplifier power to attempt to reproduce. By adding a high pass filter at a subsonic
frequency, in addition to the low pass filter, a band pass response is created. The woofer is now allowed to work
effectively at reproducing bass within the human hearing range without increased risk of damage due to over
excursion at subsonic frequencies.
Low Pass with a Subsonic Filter
dB
20 Hz
Frequency
20, 000 Hz
14
Digital Crossovers
Crossovers that accept a digital input, much like the digital equalizers discussed earlier in this lesson,
are considered digital crossovers. Perhaps the biggest advantage of a digital crossover is the flexibility and wide
range of choices for crossover points and routing to discrete outputs. By merging the almost infinite flexibility
of processing signal in the digital domain along with the signal processing function of a crossover, the digital
crossover is one of the ultimate system control tools in a system designers tool box. Perhaps the reason there
aren’t more digital crossovers available is simply one of cost. Most of the time, a digital crossover with the kind
of flexibility that is typical in such a device may be $400, $500, or much more. Add to that the cost of individual
discrete amplifier channels dedicated to each output of the crossover and the speakers to go with it, and it isn’t
long before the cost becomes overwhelming to the majority of consumers.
Multiple Discrete Outputs
Analog RCA Inputs
TosLink Digital Inputs
A Digital Crossover featuring both TosLink optical inputs or
Analog RCA inputs. The signal processing is digital inside
such a unit but converted to analog outputs so it may be used
with traditional mobile audio amplifiers that feature analog
RCA type inputs.
One nice feature that digital crossover technology has brought about is a smaller, more simplified version built into many of the top of the line headunits. Some of the top models available have RCA outputs which
can be configured to have a high pass or low pass crossover point within a pre determined range. This more simplified version of a digital crossover adds minimal cost to a headunit while adding more control over the audio
system.
A Special Note about Cascading Crossovers
There are some important considerations to note about “built in” crossovers within a headunit. If a
system uses a built in crossover or “SUBWOOFER” RCA output within a headunit, it is recommended that
any further active filtering (either from an active crossover or by a built in active crossover within an amplifier)
NOT BE USED. Use only one set of filters in a system to avoid anomalies in frequency response from “cascading” audio filters. Cascading an audio filter simply means plugging one crossed over audio signal into another
crossover for additional filtering.
Hypothetically, a system consisting of several high end audio components could have a filtering feature
built into each component. Many of the upper range components have a variety of features that are a standard
feature of those higher dollar products. The most common feature to find in amplifiers is a built in
crossover. Many headunits feature a specific subwoofer RCA preamp output that has a built in crossover. Still other headunits may even offer the choice to use the FRONT and REAR RCA preamp outputs as a High Pass output to cut off some of the lower bass that tends to muddy up the sound of front
15
door or rear deck speakers.
A headunit, for example, with FRONT/REAR/SUB preamp level outputs has at least one output filtered
already, the SUB output. Typically this will be a selectable feature in the headunit control panel to allow a crossover point (obviously Low Pass), a separate volume control to match the output levels better, and sometimes
even a “phase switch” which has a 0 or 180 degree control. If this SUB output is used, it’s NOT recommended
to use any further filtering that may be downstream in an amplifier or active crossover. In that case, an amplifier
that has a built-in crossover would be switched to “OFF” when that SUB preamp output is used.
The main problem with cascading crossovers is that the filtering function between two separate crossovers is never identical, even if the crossover point appears to be the same. To further complicate things, the
crossover points between, say, a crossover built into a headunit and crossover built into an amplifier are almost
never the same points, which creates difficulty in correcting acoustic problems once the signal gets to the speakers.
In summary, use one active crossover to perform a filtering function. Choose either the headunit, an active (external) crossover, or one built into an amplifier, however it’s important to choose ONLY one and leave
the others switched to the “OFF” position.
Amplifiers
Getting Signal to the Amplifier(s)
Once a signal passes on to an amplifier, the function of amplification is relatively easy to understand.
The signal simply increases in level so that by the time it connects to a speaker there is enough energy to move
the speaker accurately. What has become more complex though, are amplifiers with multiple channels and multiple ways to feed signal to each of the amplifier channels. These become more complex because there is more
than one right answer when considering how to plug in RCA cables or speaker wire inputs (called high level
inputs). Some multi-channel amplifiers, for example, can have a single pair of RCA inputs, but internally the
signal is routed to all of the channels. Another amplifier may have dedicated inputs where each channel has it’s
own RCA audio input made use of.
Before covering the topic of how to feed the signal into multiple channels, the type of inputs an amplifier
uses must be covered. Mobile audio systems typically have 3 choices from which to choose when determining
how to bring signal into an amplifier.
High Level Inputs
A high level input is essentially an input that connects a
headunit to an amplifier via speaker wires. Special input terminals of
the amplifier allow this type of connection. Although an RCA connection is preferred in terms of sound quality, some headunits only have
speaker wires available to use.
There are many reasons why the majority of amplifiers can’t
deal with a speaker level signal if one were to simply solder an RCA
connector on to speaker wires and use them instead of a true RCA input. Primarily the problem is that the speaker level signal (voltage) is
too high for the RCA input of the amplifier. Speaker level (high level)
and preamp RCA (low level) inputs offer the amplifier two different
“workloads” and should never be interchanged.
The high level input types on mobile audio amplifiers vary in the way they “pad down” or
“adapt” the signal level so that the amplifier can deal with it. Most high level input sections built into
the amplifier are very rudimentary and simple. They use power resistors to “choke” the signal down
so that it has much less signal voltage by the time the amplifier input section gets a hold of it. While
16
this is effective in minimizing the signal input voltage from “speaker level” voltage to “low level” voltage, the
resistors are prone to heat and increase the possibility of distortion. Some amplifiers use more sophisticated
techniques than simple power resistors, however this upgrade in quality adds cost to an amplifier. This upgrade
is a needless expense when the high level input will not be used in a system. The upgraded high level input
makes particular sense where OEM integration is part of the installation.
Line Output Converters (LOC’s)
The line output converter device is a speaker level to RCA converter for enabling headunit speaker leads to be connected to the RCA
inputs of an amplifier or processor. The headunit speaker outputs can be
from either an OEM (factory supplied) headunit or from an aftermarket
entry level unit which doesn’t have RCA outputs already built on. Either
way, it provides an external adapter that mates the two signal levels
together.
There are many types of LOC’s and many configurations. Inexpensive LOC’s may have limited compatibility to more complex OEM
audio systems as well as more propensity to noise and interference. It is
always recommended to use the best quality LOC possible. This way,
the “link” between the OEM and aftermarket audio components is not the weak link of the audio signal path.
Typically, OEM headunits have a wider variety of “floating ground” output types and signal (voltage)
levels than that of aftermarket headunits. This variety is enabled because the vehicle manufacturer has total control over the amplifier and other components used within the audio system in addition to the factory headunit.
Aftermarket manufacturers generally stick to an output style (floating ground most of the time) that is adapted
well by an LOC.
The main challenge with any OEM headunit or any aftermarket headunit that is to be connected to an
LOC is how much signal level will be fed into the LOC. Many of the inexpensive, entry level LOC’s can’t
handle the “Mosfet” high power headunit output levels without overheating. Absolutely avoid using a high powered headunit into an LOC that isn’t rated to handle the power levels. The result could be damaged components
or even, in the worst cases, smoke or fire.
The use of a high quality LOC is an excellent alternative to replacing a headunit in a vehicle that has an
odd shaped or uniquely integrated OEM system. The use of a high quality LOC will provide good signal output
that can then be processed by either a signal processor or by an amplifier. LOC’s offer an excellent opportunity
to satisfy a customer without having to tear out their factory radio in the process. Some OEM headunits are considered to be a premium system component It may be necessary to use a special application LOC specific to that
type of audio system and vehicle.
Some of the systems known to need these special components are vehicles with OEM Bose audio systems (Mercedes Benz, Audi, Nissan, Acura, and select GM vehicles), OEM Ford/JBL and Mach systems in Ford
and Lincoln vehicles, OEM Harmon Kardon systems in Jaguar and some BMW 3 series vehicles, OEM Alpine/
Dynaudio systems in some Volvo vehicles, OEM BMW 5 and 7 series systems with DSP built-in (1996 and
newer ), Chrysler/Infinity systems in Chrysler, Dodge, and Jeep vehicles, as well as Lexus vehicles with Nakamichi or Mark Levinson OEM audio systems. When doing OEM additions to these factory supplied systems,
consult with a lead installer and the Tag Zone site to verify the necessary LOC or interface device required to
add an amplifier.
For instance, in most Lexus vehicles, the factory headunit does not have a remote turn-on output that
will turn an amplifier on, but the appropriate adapter can provide the turn on output when it “senses” an audio
signal. There are far too many variables to guess about an appropriate product to use. An installer must
do the brief, but important research to be sure the LOC device will work for the chosen application.
Once this is completed and the device is installed and operating correctly, the customer has the percep17
tion that their mediocre OEM audio system has just gotten a whole lot better.
Low Level (RCA) Inputs
By far the input of choice, low level inputs are designed
to connect directly to the RCA (low level) outputs of a headunit,
LOC, or signal processor. The difference between high and low
level amplifier inputs is primarily the voltage level of the audio signal. Unlike high level inputs (speaker level audio signal voltage),
the low level input consists of lower voltage levels and is much
cleaner (meaning lower distortion). Using the low level inputs allows the signal to bypass the distortion producing circuitry needed
if the high level inputs are used. The signal moves directly to the
amplification stage of the component with little or no change in
signal purity.
Gain Control / Input Sensitivity
Nearly every mobile audio amplifier has RCA type analog audio inputs.
It This has become the standardized connector type within the mobile electronics
industry. The majority of mobile audio
amplifiers are set up to accept a range
of input voltage on the signal that feed
the RCA jacks. The speaker level signal
(voltage) generally exceeds the upper
limit of this range. Not every amplifier has an identical input voltage range
however. In fact, it is entirely possible
for very high quality, high signal voltage
headunits or signal processors to exceed
The gain control is generally located near the RCA
the input range of the amplifier even with
inputs on most mobile audio amplifiers
the same RCA (low level) audio signal.
The input range of the amplifier must be
level matched to the amount of signal voltage that the device upstream is feeding into it. This is what the function of the gain control (sometimes called input sensitivity) serves in an amplifier. The gain control is designed
to match audio signal levels between the various components of an audio system. People often mistake the gain
control for a secondary volume control. The gain control on the amplifier IS NOT a volume control.
The Amplifier Gain Control IS NOT a Volume Control!
18
Once the voltage level is matched, the amplifier can be expected to generate a specified amount of output power. In an ideal situation, and with reputable brands, the output power should meet or exceed the rated
specification when the proper attention has been given to input gain adjustments. Take the following specifications as an example, then follow the suggested basic procedures.
System Components - A CD Headunit and (1) two-channel amplifier connected to (2) full range, 4 ohm
door speakers.
Amplifier input signal range (input sensitivity) - 0.5 volts to 4 volts
Amplifier Output Power (rated RMS power) - 100 watts/channel @ 4 ohms
Headunit signal output level (on the RCA’s) - 3.6 volts at MAX volume
Based on the parameters above, the amplifier SHOULD put out at least 100 watts into each door speaker
when the input sensitivity is adjusted to be slightly more than the minimum setting of 4 volts (i.e. about 3.6
volts). If it were adjusted all the way up to 0.5 volts, the amp would be looking for a very low signal level to
amplify. When it sees the higher input levels of 3.6 volts from the headunit in the 0.5 volt position, the input
section becomes overloaded and the 100 watts of output (though still 100 watts) becomes heavily distorted and
can burn up the door speakers. Adjusting the gain higher means moving it to a lower voltage position. In effect,
increasing the gain tells the amplifier to increase the amplification of the signal. With higher signal input levels,
the amplifier gain can be set lower and (generally) run cooler and more reliable.
What if the volume isn’t enough in the 3.6 volt input sensitivity position? Wouldn’t the gain just get
turned up? Isn’t that the answer when things aren’t loud enough? NO-NO-NO! If it’s not loud enough, the system needs more power or you need to address some other flaw in speaker placement or connection. Turning up
the gain beyond the level matched position is a quick way to speaker failures and audible distortion. While some
systems can tolerate a little more gain increase to account for listening to music (rather than the test tone signals
used at the amplifier factory), there is a practical limit to what will sound acceptable and keep the speakers safe.
Signal Distribution / Signal Steering
The way in which signal is routed to multiple amplifier channels is known as signal distribution or signal
steering. It’s all about the way that an audio signal can be directed toward more than one single location.
Here’s an example of where steering or distributing signal to multiple channels from a single audio
output might take place. Take the example of a CD headunit that features one RCA preout. The head unit is to
connect directly to a four channel amplifier. The problem is, with only two channels of output from the headunit
(one left channel and one right channel), how will the amplifier receive audio input for four channels?
Most multi-channel amplifiers provide an option for the way that they “look” for input signals. In the
above example, it is highly likely that the installer could configure the amplifier to have the first two channels
(left and right) internally “jumper” their audio signal to the remaining two channels. This is just like splitting the
signal outside of the amplifier but much cleaner and less likely to generate noises or interference. Signal steering may be as simple as selecting a position on an input switch located near the RCA input connectors of the
amplifier.
While every amplifier will differ, the majority of multi-channel mobile audio amplifiers allow for some
flexibility in how the signal is fed into the amplifier channels. Typical configuration is done by correct positioning of the signal distribution (input) switch(es).
“Y” Adapters
The use of RCA splitters or “Y Adapters” is another way to split signal from a single source to
feed more than one input. The correct use of Y adapters is crucial to the amplifier signal performance.
The Y adapter is meant to be used as a “1 into 2” configuration meaning that one output can be split
into two destinations. DO NOT use Y adapters for a “2 into 1” configurations, where two separate
19
signal sources are joined together into one common input. This will create confusion at the input of the amplifier
because the amplifier will attempt to process BOTH signals. If the signals are different, such as a right and left
channel, the amplifier will create a summed signal that is the combination of both. In this case, the signal would
become left plus right (L+R) mono and no stereo separation is the end result.
An example of a “Y Adapter” packaged and out of the package. The “Y
Adapter” on the right is called a “male to 2 female” style, “Y Adapters” are
available in many varieties of male and female configurations to suit nearly
every connection need.
The Output of the Amplifier
Two Channel Configuration
Once the amplifier has done it’s job of increasing audio signal levels to the point where they can drive a
speaker, it’s time to connect the output of the amplifier to the speaker(s).
Perhaps the simplest and most common connection of an amplifier to a speaker is that of the basic two
channel amplifier connected to a pair of speakers. In this scenario, each of the two (2) channels of the amplifier are designed to be connected to a single speaker. The installer needs only to ensure that the polarity of the
speakers matches that of the output of the amplifier. That is to say that the installer needs only to match the
LEFT channel of the amplifier to the LEFT speaker and the RIGHT channel of the amplifier to the RIGHT
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20
speaker. In addition, the positive terminals (+) and negative terminals (-) must be matched to the appropriate
connections on the amplifier. This type of connection is illustrated below.
Although most installers know this fact already, the amplifier (+) and (-) outputs must be connected to
the (+) and (-) speaker terminals. Any speaker wire connected to ground or anything but the speaker itself will
typically cause the amplifier to go into some type of premature failure mode, if it works at all. Never connect an
amplifier output or any speaker leads to the chassis or to (-) ground, period.
Bridging an Amplifier
Bridging an amplifier is a term used to describe an output configuration that combines the individual
maximum power contained within EACH channel into one single, more powerful output channel. The term
“bridging” reflects a connection (or bridge) between two channels. Bridging offers an effective way to maximize the power output of an amplifier, however bridging also requires additional power consumption from the
vehicle electrical system when the overall output power of the amplifier has increased. In effect, it’s simply a
method to maximize the output power potential of two channels into one, but it’s not without additional current
consumption. For example, an amplifier that has a maximum output of 200 watts x 2 (two-channel) for a total
of 400 watts has the same electrical power consumption as a 400 watts x 1 (bridged) configuration. Either way,
400 watts of power output requires similar amounts of electrical supply.
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Making the Bridged Connection
The method of bridging an amplifier depends on the brand. Some amplifiers require that a switch be
engaged to tell the amplifier circuitry to bridge the internal channel pair into one single channel. Others are
bridged simply by the method used to connect the output. The typical car audio amplifier has a labeled section
near the output terminals which designates certain terminals as the (+) and (-) terminals when using the output
in a bridged configuration. It is extremely common to see the LEFT (+) and the RIGHT (-) become the bridged
channel (+) and (-) terminals on many mobile audio amplifiers. While this is not the case with all products, it’s
one of the common configurations.
If an amplifier has the capability of bridging, the installer MUST ALWAYS refer to the installation manual to verify the appropriate method for connecting the amplifier in a bridged configuration.
Improper connection may cause damage to both the speaker(s) and to the amplifier.
21
Multiple Speakers
One speaker connected to each amplifier channel is a relatively easy job for the amplifier to do. The
difficulty for some amplifiers becomes driving more than one speaker per channel. What many installers do not
realize is that, even if the collective load of multiple speakers is the same as one speaker (i.e. 4 ohms for example), the number of voice coils the amplifier must move is what makes the difference.
When an amplifier moves a speaker in and out to compress and rarefy air, it must effectively “start” and
“stop” the driver with an accuracy that matches the input signal. When the audio signal does something, the amplifier output must drive the speaker to do exactly the same thing. It’s more challenging for an amplifier to drive
four 4-ohm speakers than to drive one 4-ohm speaker, even if the four speakers are wired to a “4-ohm load”.
Series Connections
When speakers are connected to an amplifier channel in a series configuration, they will be connected in
such a way as to allow current from the amplifier to flow through only one path. Much like the Christmas lights
that are available to decorate homes around the holidays, one break in a series connection disrupts the operation of the whole group of “loads” (i.e. speakers) in the circuit. This means that if a speaker has blown or failed
somehow, it affects the remaining speakers connected to that channel of the amplifier. The series connection
WILL NOT allow the other loads connected to continue working normally.
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What impedance “AC resistance” would the amplifier see. In other words what “load” would be
on the output of the amplifier? REMEMBER series resistance from earlier lessons? The formula
would be R1 + R2 + R3 ... = Rt. If the speakers are 4 Ohms apiece, the math would look like:
4Ω + 4Ω = 8Ω
The amplifier will have an 8 Ohm load on its output.
22
Parallel Connections
When speakers are connected to an amplifier channel in a parallel configuration, they will be connected
in such a way as to allow current from the amplifier to flow through multiple paths. When there are multiple
paths for current to flow, one break in a parallel connection WILL NOT disrupt the operation of the whole group
of “loads” (i.e. speakers) in the circuit. This means that if a speaker has blown or failed somehow, it won’t affect
the remaining speakers connected to that channel of the amplifier. Instead, the parallel connection allows the
other loads connected to continue working normally.
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What impedance “AC resistance” would the amplifier see. In other words what “load” would be on
the output of the amplifier? REMEMBER parallel resistance from earlier lessons? The formula would
be 1 / (1/R1) + (1/R2) + (1/R3) ... = Rt. If the speakers are 4 Ohms apiece, the math would look like:
1
1
1
+
4Ω
4Ω
=
2Ω
Series-Parallel Connections
When speakers are connected to an amplifier channel in a series-parallel configuration, they will be
connected in such a way as to allow current from the amplifier to flow through only one path between
series connected speakers (or voice coils) and multiple paths where there are parallel connections. A
common example of series-parallel connections is found when wiring multiple dual voice coil drivers
to a single channel of an amplifier.
23
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(Combining the power of BOTH channels into
one single channel but with multiple speakers)
Notice this connection.
4Ω
4Ω
Amplifier Output Diagram
Notice this connection.
4Ω
Right Channel (-)
Becomes (-) Output
-
Left Channel (+)
Becomes (+) Output
+
4Ω
What impedance “AC resistance” would the amplifier see. In other words what “load” would be on
the output of the amplifier? This takes a closer look. Let’s start be looking and solving for the series
connections.
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4Ω
4Ω + 4Ω = 8Ω
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Solution for Path 1
Really two 4Ω Speakers that
look like one 8Ω speaker
mathematically.
Bridged Output Configuration (Parallel)
8Ω
4Ω
8Ω
4Ω
Right Channel (-)
Becomes (-) Output
Left Channel (+)
Becomes (+) Output
4Ω
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-
+
4Ω + 4Ω = 8Ω
Solution for Path 2
Right Channel (-)
Becomes (-) Output
-
Left Channel (+)
Becomes (+) Output
+
Really two 4Ω Speakers that
look like one 8Ω speaker
mathematically.
24
Solving for the Parallel 8Ω looking speakers makes the load 4Ω.
1
1
1
+
8Ω
8Ω
=
4Ω
A Special Note About Wiring Dual Voice Coil Speakers
Dual voice coil (DVC) speakers are speakers which have 2 voice coils that move one cone. Most dual
voice coil speakers are subwoofers. This adds even greater power handling and wiring flexibility to a system.
Wiring dual voice coil woofers is the same as wiring two separate woofers. The same rules for series or parallel
wiring apply. The only important concern with a DVC woofer is that it needs to have a mono input signal. This
means it should be either ALL LEFT or ALL RIGHT, unless you are combining the signals through a BRIDGING process in the amplifier or in a signal processor. The signal fed to the subwoofers then becomes L+R mono
and that’s perfectly okay.
Each voice coil needs to play the SAME INFORMATION because they’re connected to the SAME
SPEAKER CONE. You could imagine the difficulty a woofer might have playing one voice coil of left channel
information, while the other voice coil fights to play the right channel information.
Power and Antenna Connections
Getting Power to the Components
This section will deal with the basic power and antenna connections needed for headunit installation.
This, along with headunit speaker connection, will provide you with a clear understanding on this most fundamental of installation projects. In addition, powering a signal processor will also be discussed in detail.
Connecting Power to the Headunit
In most cases the connection of a headunit into a vehicle wiring harness will be as simple as using the
appropriate wiring harness adapter. Virtually all late model vehicles have wiring harness adapters available. This
is by far the most common method of interconnection. Occasionally, you will actually have to figure out the
wiring of the vehicle on your own. This occurs on older model vehicles as well as those where the factory wiring harness has been damaged.
Wiring Harness Adapters
Most installations will require the use of a wiring harness
adapter. The adapter essentially plugs into the same receptacle that once
plugged into the factory supplied head unit. By using a wiring harness
adapter, the installer can wire the adapter to the electrical plug supplied
with the headunit outside the vehicle (on the bench) and make the installation of the new headunit essentially a “plug-in” exercise. Always
connect the wiring harness adapter to the headunit’s electrical plug
25
BEFORE plugging into the vehicle electrical harness. This will eliminate the possibility of accidentally shorting
out a memory or accessory wire during the installation process.
EIA Wire Color Code Standards
Most wiring harness adapters adhere to a standardized wire color-coding. This is called the “EIA (Electronic Industries Alliance) Wire Color Standard.”. The EIA encourages all manufacturers of head units to follow the same standard. Although not every headunit follows these color code standards, the majority of name
brands do follow the standards.
EIA Wire Color Code Standard
Yellow
Red
Black
Orange
Blue
Blue/White
White
White/Black
Gray
Gray/Black
Green
Green/Black
Violet
Violet/Black
Constant +12v
Accessory +12v
Chassis Ground
Illumination +12v
Power Antenna +12v
Remote Turn-on +12v
Left Front Speaker (+)
Left Front Speaker (-)
Right Front Speaker (+)
Right Front Speaker (-)
Left Rear Speaker (+)
Left Rear Speaker (-)
Right Rear Speaker (+)
Right Rear Speaker (-)
AM/FM Antenna Connections
The Motorola Plug
The Motorola plug is the world standard of AM/FM antenna connections. Virtually all aftermarket antennas and headunits use this plug as a
standard. Unfortunately, not all vehicle manufacturers use the Motorola plug,
which makes direct connection to the headunit a potential problem.
Besides the Motorola plug automobile manufacturers use many other
common standards that installers will run into in the vehicle. The following are some that you will run into.
Mini-Motorola Plug
The “mini” version of the Motorola plug is found on 1992 and
later General Motors vehicles. This includes Chevrolet, Buick, Cadillac, GMC, Oldsmobile, Pontiac, and Saturn brand names.
26
Dual Diversity Plug
The Dual Diversity AM/FM antenna system is typically found on Nissan and
Infiniti vehicles and occasionally on some Lexus models. It’s basically a Motorola
plug on one side and a reverse Motorola plug (female) version on the other. The diversity tuner in the OEM radio draws signal from the stronger of two antennas.
Ford Vehicle (95 and newer) Antenna Connector
Some Ford, Lincoln, and Mercury vehicles use a proprietary
antenna connector type. A standard Motorola input connector will not
work with these connectors unless an adapter is used.
German Antenna Connector
Some German vehicles such as VW and Audi use a special round
head connector that is unique to those vehicles. A standard Motorola input
connector will not work with these connectors unless an adapter is used.
All of these proprietary connectors have commercially available
adapter solutions in the installation bay. Consult with your Installation Manager if you have further questions about a particular AM/FM antenna situation.
Connecting Power to Signal Processors
Most signal processors, regardless of the type, consume fewer than 5 amperes of current. Due to the
relatively low current requirement, 18 gauge wire that is readily available in the installation bay is ideal for use
to power a signal processor.
A signal processor simply requires three fundamental wires to operate.
1) A constant +12v supply of power (fused appropriately, usually 1-2a)
2) A good chassis ground (can be shared with other nearby components)
3) A remote turn-on input (shows +12v when the headunit turns on)
27
While there are no hard and fast rules about which colors are used, the majority of installers feel comfortable with using RED or YELLOW for the +12v connection, BLACK for the chassis ground, and BLUE for
the remote turn-on input.
When connecting to a common grounding point, it is important to connect so that each electrical device
has a benefit of the full ground potential. This can be accomplished by a Single Point Grounding (SPG) technique, or through a ground distribution block accessory. Single Point Grounding offers an easy way to connect
several different sizes of cable to the chassis because each connects to a ring terminal and then all of the terminals are attached to bare metal with one single screw or bolt. That’s where the term “Single Point” comes from.
Ground distribution is a cleaner way to connect multiple large gauge wires and have one single super sized wire
connect to a metal point of the vehicle. It’s essentially a Single Point Ground, but with more visual presentation
taken into account with the use of a distribution block.
Connecting Power to Amplifiers
Amplifiers Waste Power
Amplifiers have the really serious task of consuming power from the vehicle electrical system to make
audio more powerful. Instead of “making” power, an amplifier actually “consumes” power and then proceeds
to waste some of it in the conversion to audio output. If an amplifier was 100% efficient at converting power
that it “consumes” into power “output”, there would be no additional heat in the process. Anyone who has ever
touched an amplifier heatsink after it has been running for a while knows there’s plenty of heat exchanged. The
heat represents some of the inefficiency in the process of “amplifying” the audio signal.
This inefficiency is inherent in every mobile audio amplifier, regardless of brand or class. The majority
of mobile audio amplifiers on the market fall under a Class AB type classification, which is about 50% efficient
at full power output on average. Many amplifier manufacturers have devised ingenious ways to manage the heat
better so that the efficiency becomes even higher than 50%, but there’s still going to be inefficiency to a great
degree. For this reason, it is vitally important to supply the proper size power and ground cables to the amplifier.
Higher powered amplifiers require bigger cables to do the “work”.
Regardless of the amplifier brand or type, all mobile audio amplifiers require three basic connections.
1) A constant +12v supply of power (fused appropriately at the battery)
2) A good chassis ground (can be shared with other nearby components)
3) A remote turn-on input (shows +12v when the headunit turns on)
Connect at the (+) Battery Post
For the (+) positive connection to the amplifier,
the connection MUST be connected at the (+) terminal
of the vehicle battery, either directly or via distribution
block. The (+) cable must have a fuse placed as close as
possible to the positive battery post to protect the wire
that runs through the vehicle.
The (+) positive connection for an amplifier typically requires MUCH MORE current than can be found
under the steering column or at the fuse panel could
provide. Going directly to the (+) battery post eliminates
any weak links in the electrical circuit when the amplifier
seeks to consume electrical energy.
28
The gauge (thickness) of wire used to supply amplifiers is typically much larger than most other circuits
within the vehicle. This underscores the need for going directly to the battery for the power connection. For
more information about specific requirements for determining the appropriate wire gauge for a particular application, please consult the Wire Gauge Principles Workbook.
Connect to a Low Resistance (Low Voltage Drop) Ground Point
The (-) negative “ground” connection is equally as important as the positive connection. The fundamental function of an electronic circuit requires an equally potent path of current flow for the return side (often
known as the “ground” side) of the circuit. In simple terms, there are three critical elements to a good, equally
potent electrical ground path.
1) The ground cable should be of equal potential to the power cable. This is most often accomplished by simply using the same gauge of wire for the ground connection as was used for the power connection. Although
the ground cable is typically shorter than the run of power cable up to the battery, the ground cable gauge (or
thickness) must rely on the chassis connection to make the return path back to the (-) negative battery post.
It’s just a smart move to eliminate any potential electrical resistance by keeping the cables for BOTH power
and ground the same size.
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2) The physical connection of the amplifier ground to the body or chassis of the vehicle is the next important
point to consider. The metal to which the ground cable connects to MUST be a point where the connection
to the (-) negative battery post is equally potent, meaning a low resistance measurement. The Fundamentals of Multimeters Workbook offers two methods to measure a low resistance ground point in the Practical
Activities sections of “Measuring Resistance” or “Measuring Voltage”. Measurement with a Multimeter will
give an indication of a BAD ground point right away. The ultimate ground point test is using the “Measuring Voltage” method to check the ground again AFTER the amplifier is installed and drawing current. A low
voltage drop between two ground points verifies the ground is good under a load.
Typically, drilling a hole and attaching a ring terminal and star washer to a metal point on the body or frame
is the correct way to ground an amplifier. Use a screw that grabs into the metal and tightens the ring terminal
securely to the metal. It is also important to scrape some paint away from the metal to reduce any resistance
in the connection. Cover any scraped paint with a light coating of grease or paint to inhibit any rusting of the
area in the future.
When connecting several amplifiers to a common grounding point, it is important to connect so that each
amplifier has the benefit of the full ground potential. As outlined previously, this can be accomplished by a
Single Point Grounding (SPG) technique, or through a ground distribution block accessory. Single
Point Grounding offers an easy way to connect several different sizes of cable to the chassis because each connect to a ring terminal and then all of the terminals are attached to bare metal with
one single screw or bolt.
29
1
2
3
4
When checking a possible ground spot,
scrape the paint away and test the amount
of resistance between the ground point
and the (-) negative battery post. A low
resistance reading on the Multimeter indicates a good place to try. The measurement shown of 0.2 ohms (based on meter
calibration and probe lead resistance), is
excellent in most cases. Always verify a
good ground AFTER the amplifiers are
up and running by using the “Measuring
Voltage” exercise while the amplifiers are
drawing current under load.
3) The final important portion of the (-) negative ground connection of the amplifier is actually at or near the
(-) battery post of the vehicle. Be sure to inspect the terminals of the battery (both (+) and (-) ) and the cable
that connects the (-) battery terminal to the vehicle body or chassis. Remember the basics of DC electricity;
any point of resistance within the circuit path can be a weak link and one weak link is all it takes to compromise the entire electrical supply of that circuit.
Often, it may be necessary to attach a supplemental ground connection (a second or additional cable) to the
body or chassis of the vehicle to “beef up” the electrical potential of current flow along the chassis to the
(-) negative battery post. Audio systems that use several amplifiers should use this technique to ensure that
the electrical circuit has no weak links. It is ALWAYS necessary to check on BOTH SIDES of the area that
is going to be drilled into to attach a ground connection for the amplifier. Without checking, damage may
occur to things on the other side of the body or chassis metal such as brake lines, fuel lines, air conditioning
lines, or wiring harnesses. Remember the old saying, “Check Twice- Drill ONCE”.
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30
A Special Note Concerning Ground in Fiberglass Vehicles
Most of the ground connection rules of thumb discussed are applicable to nearly every car on the road
today with some exceptions. Fiberglass bodied vehicles such as Chevrolet Corvettes and “Kit” cars will not
have any conductive body panels that will serve as a ground plane. Instead, either the actual steel frame of the
car (if equipped) or the (-) negative battery post is the location that must serve as the ground point for all electrical connections to be made.
Modern vehicles are increasingly using composite materials to form outer body panels such as door
skins, trunk lids, and hoods. While the weight savings increases fuel efficiency, composite materials don’t provide a reliable conductive ground point. When these composite materials make up the entire body (or the majority of it), it’s best to use the (-) negative battery post as the location for ALL ground connections to be made.
In addition to fiberglass vehicles, marine vessels such as boats and personal watercraft should be approached the same way with ground connections for any accessory equipment to be added connected directly to
the negative (-) terminal of the battery.
Remote Turn-On Connections
Most headunits provide a BLUE or BLUE/WHITE wire that will send +12 volts to any of the connected
devices when the headunit turns on so that each devices “knows” when to activate. This way amplifiers and
signal processors aren’t always on and consuming energy.
The area of concern is when too many devices need to connect to this remote turn-on output. Typically,
the remote turn-on output is current limited to an output of less than 1 ampere. Each amplifier requires a different amount of current to turn on, but it’s generally a good assumption to say that a single remote turn on lead
can “turn-on” TWO AMPLIFIERS (two devices) safely. This assumes a current requirement of 500 milliamperes or less to turn the amplifier on. When more than two amplifiers require turning on, it’s advised to use an
SPDT relay to increase the current supply to the remote turn on terminals of each amplifier.
Follow the diagram shown for adding a relay to turn on multiple amplifiers. Use this approach whenever the
remote turn-on lead must turn on more than two amplifiers.
Using an SPDT (Bosch Type) Relay to buffer a Remote Turn-On Lead
Output to Amplifier(s)
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Constant +12v Source
(Add a 5 amp fuse)
Beyond these basic steps, be certain that all connections at the amplifier are securely tightened
and that the amplifier has a secure mount. An unmounted amplifier that moves around could potentially
cause the power and ground wires strain and pull them loose unexpectedly.
31

Audio Component Interconnection - Pro

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