Troldtekt® acoustics woodcrete panels

Transcription

11/29/2005
Building Technology and Architectural Design
Program 9nd lecture
8.30-9.15 Case studies – Room Acoustics
9.15–9.30
9.30–10.15
Break
Case studies – Room Acoustics
Lecturer
Poul Henning Kirkegaard
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P.H. Kirkegaard - Department of Civil Engineering
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Troldtekt® acoustics woodcrete panels
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Prints on acoustics panels
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Rockfon acoustics panels
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Gyproc acoustics panels
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Concert Hall Acoustics - an Overview

There are three basic types of concert hall
architectures: the shoebox, the vineyard and the fan
form.
The classical halls of the nineteenth century were
narrow, high, rectangular shoeboxes. These are halls
like the Amsterdam Concertgebouw (1888), the Vienna
Musikvereinssaal (1870) and the Boston Symphony Hall
(1900).

The second form, the vineyard, is often made of layered
terraces or arenas with prominent diffusing upperreflector surfaces. The audience is devided into smaller
sub-seating-areas. These are often asymmetrical and
create useful early reflections into all sections of the
audience. A typical vineyard hall is the Berlin
Philharmonie (1963).

The third form, the fan type, proved unsuccessful nearly
everywhere. This form was somehow common in the
mid-20th century.
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The shoe box - Royal Festival Hall.
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The vineyard - Berlin Philharmonie
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The fan-shaped - Barbican Hall, London
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Clarity C80, C50 (dB)

The measurement of Clarity is the ratio of the energy in the early
sound compared to that in the reverberant sound, expressed in dB.
Early sound is what is heard in the first 80 msec (C50 - 50 msec)
after the arrival of the direct sound. It is a measure of the degree
to which the individual sounds stand apart from one another.
If the clarity is too low, the fast parts of the music are not
"readable" anymore. C80 is a function of both the architectural and
the stage set design.
If there is no reverberation in a dead room, the music will be very
clear and C80 will have a large positive value. If the reverberation
is large, the music will be unclear and C80 will have a relatively
high negative value. C80 becomes 0 dB, if the early and the
reverberant sound is equal.
Often the values for 500Hz, 1000Hz and 2000Hz are averaged. This
will be expressed by the symbol C80(3). For orchestral music a C80
of 0dB to -4dB is often preferred, but for rehearsals often
conductors express satisfaction about a C80 of 1dB to 5dB, because
every detail can be heard. For singers, all values of clarity between
+1 and +5 seem acceptable. C80 should be generally in the range
of -4dB and +4dB.
For speech, in comparison to music, the Clarity will be measured as
the ratio of the first 50 msec (C50) instead of 80 msec (C80) for
music.
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'Deutlichkeit' (Clarity) D-50
Deutlichkeit is the ratio of early sound energy to
the total sound energy. In concert hall acoustics it
refers to the degree to which individual strands in
a musical presentation can be differentiated from
each other.
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Initial Time Delay Gap ITDG (msec)
The time difference between the arrival of the
direct sound and the first significant reflection (at
a listener's seat in the hall). It corresponds to the
subjective impression of 'intimacy'.
Preferred values don´t exceed 20 msec.
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Intimacy LTDG msec
The initial time delay gap measured near the center of the main
floor. It is generally determined by the first sound reflection of a
side wall or a balcony front after arrival of the direct sound.
The music should sound as if heard in a small hall - the listeners
should feel an intimate contact with the performers.
Texture
Texture is the subjective impression the listeners derive from the
patterns in which the sequence of early sound reflections arrive at
their ears. Good texture requires a large number of early
reflections, uniformly but not precisely spaced apart, and with no
single reflection dominating the others.
Spaciousness
Is supported by early reflections that arrive from near lateral
directions.
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Diffusion
Every successful hall for music has irregularities, both large and small, on
walls, balcony faces and ceilings which create a rich and dense sound
structure. Such irregular surfaces diffuse the high frequency portions of the
early reflected sound waves, adding patina to the overall sound.
Stage Support
is a measure of strength of orchestral sound returned by nearby reflecting
surfaces to the ears of each player in the orchestra, the acoustical support,
that a hall gives a player on stage.
Measured as the ratio of the arriving sound energy at the first 10 msec and
the arriving sound energy between 20 and 100 msec.
Measurement source is an omnidirectional sound source in a distance of 1
meter. The sound arriving in the later interval has been reflected in the hall
and the stage environment already. The measurements are made at several
positions and the data are averaged.
Strength G (dB)
The strength G is defined as the difference between the sound level in dB at
listeners position in the hall and the level of the same source in free field in
the reference distance 10 m from the centre of the source.
The strength of the sound, which is related to loudness, is a quantity that
must be as uniform as possible throughout the hall.
Interaural Cross Correlation Coefficient IACC
The measure of the difference in the sounds arriving at two ears of listener
facing the performing entity in a hall. IACC is usually measured with a
dummy head.
IACC3 is the average of IACC's for the three octave frequency bands with
center frequencies of 500, 1000 and 2000 Hz
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Bass Ratio, Bass Strength BR
BR is a measure of the support which the reverberation in the hall gives to the low
notes of the music. The Bass Ratio is objective counterpart of the subjective criterion
"Warmth". It is the ratio of RT between low frequencies (octaves 125 and 250 Hz) and
medium frequencies (octaves 500 and 1000 Hz).
The preferred values of the BR are between 1.1 to 1.25 for halls with high RT's, and
1.1 to 1.45 for halls with RT's of 1.8 sec or less.
Envelopment
Envelopment is quantified by the amount of sound that comes not directly from the
source. But the total amount of sound that comes on the horizontal plane on a
listener's position. Can be displayed in a soundrose, a circular representation of the
directions from which a listener receives sound impulses.
A hall with good lateral (side wall) reflections usually has a better feeling of
intimacy. Halls are designed with the goal to let the hall sounding as small as possible.
That way the audience feels up close and personal with the orchestra.
%ALCONS (%)
The measured percentage of Articulation Loss of Consonants by a listener. %ALCONS
is derived from the direct to total arriving sound energy ratio.
%ALCONS of 0% to 3% indicates perfect clarity and intelligibility with no loss of
sentence understanding, while 10% and beyond is growing toward poor intelligibility,
and 15% typically representing the maximum loss acceptable.
Echoes
The room and stage must be free from audible echoes
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Diffusers
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Strategies to Mitigate Sound Focusing
1) Stepped gradations for
the auditorium ceiling; (2)
Suspended convex reflection
panel at center of ceiling;
(3) Retractable soundabsorbing curtains and
curtains for the front
portions of the glass
sections of the auditorium
walls.
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Challenges in Modeling this Auditorium
Large number of faces
Curved surfaces approximated with planar surfaces
Sensitive to absorption & scattering coefficients
Large surfaces
“If in doubt, try with both high and low values [for scattering
coefficients] and see if the results are sensitive or not (it
depends on the hall shape and the absorption distribution and is
very difficult to know in advance).”
- Bengt-Inge
Dalenbäck (CATT user’s web page)
Coupled room
Transmission coefficients for some surfaces
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Music Center at Strathmore
The Music Center at Strathmore
in Montgomery County Maryland
has a particularly complex and
grand array of variable acoustic
devices that required a control
system that could organize,
display, and execute the
movement and position status
of 110 electro mechanical
elements.
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Acoustic adjustment of rooms
The system modifies the hall’s acoustic in a natural way by
filling in the missing reflections from each surface and can
even, electronically, move those surfaces to acoustically
more desirable positions.
— Microphones to capture the sound on stage and in the
auditorium
— Loudspeakers discretely positioned around the auditorium
to reproduce the missing reflections and reverberation
— Central equipment comprising an advanced digital
processor, amplifiers, and a control panel for selection of the
acoustic settings and other functions such as line input and
line output
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Concert Hall Danish Broadcasting Corporation
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Thank You
for
Your Attention
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