common sound levels and the decibel scale

COMMON SOUND LEVELS AND THE DECIBEL SCALE
• The loudness of a sound depends on its sound pressure level, which is expressed in units of
decibel (dB).
• Most sounds we hear in our daily lives have sound pressure levels in the range of 30dB to 90dB.
• The numerical values of two separate sounds do not directly add to one another. If a sound of
70dB is added to another sound of 70dB, the total is only a 3 dB increase (to 73 dB), not a
doubling (to 140dB).
• In terms of sound perception, 3 dB is the minimum change that most people can detect.
• Every 10 dB increase in sound level is heard as a doubling of loudness.
• Community sound studies use an A-weighting scale (dBA) that approximates the response of the
human ear to sounds experienced in everyday life.
• Typical A-weighted sound levels from everyday life are presented in the attached chart.
• The C-weighting scale was designed only for exposure to very loud sounds over 90 dB.
• It is important to use the A-weighting scale in wind turbine sound studies, where the audible
sounds are in the quiet range of 25 to 45 dBA; use of the C-weighting scale would artificially
inflate low-frequency sound.
• The Michigan Siting Guidelines for Wind Energy Systems recommend a 55-dBA limit at a
project’s external property line.
COMMON SOUND LEVELS AND THE DECIBEL SCALE
Sound Levels
(dBA)
105
Lawn Mower at 3’
Truck Passby 50 mph at 50’
Conversational Voice at 3’
Train Horn
95
85
Tractor / Combine at 50’
75
Car Passby 50 mph at 25’
65
55
Crickets / Tree Frogs
Freight Train 1/2 mile away
45
Quiet Rural Area at Night
Quiet Suburban Area at Night
35
25
Whisper
15
Threshold of Hearing
0