In environmental noise monitoring, the "A-weighting" (dBA) scale is most commonly used because
- AIt measures the absolute physical power of sound waves.
- BIt gives more weight to very low-frequency infrasound.
- CIt filters sound to mimic the human ear’s varying sensitivity to different frequencies.Correct
- DIt accounts for the speed of sound in humid conditions.
Solution
Concept
A-weighting human auditory frequency response
Formula
NONE
Step-by-step solution
1. Human hearing does not perceive all sound frequencies with equal loudness. 2. The human ear is relatively insensitive to very low frequencies and very high frequencies, exhibiting peak sensitivity around 1 to 4 kHz. 3. The A-weighting filter de-emphasizes low and high frequencies to match the inverted 40-phon Fletcher-Munson equal-loudness contour. 4. Therefore, dBA is standard because it mimics the varying sensitivity of the human ear. Answer: C
Explanation
The A-weighting scale (dBA) is an electronic filter network applied to sound level meters to emulate the frequency response curve of the human ear at moderate loudness levels. Human hearing is significantly less sensitive to low-frequency rumble and extremely high frequencies while most sensitive between 1 kHz and 5 kHz, which the A-weighting curve accurately reproduces.
Why the other options are wrong
A) Absolute physical power of sound waves is measured by unweighted linear decibels (dBZ or dBL). B) Low-frequency infrasound is strongly attenuated by A-weighting rather than amplified. D) The weighting scale represents human auditory frequency sensitivity and is independent of ambient humidity effects.
Shortcut
A-weighting = Auditory mimicry (matches human ear sensitivity curve).
Common mistake
Believing the A-scale measures total physical sound energy rather than psychoacoustic human response.
Correct answer: C) It filters sound to mimic the human ear’s varying sensitivity to different frequencies.