What is the purpose of A-weighting sound pressure?

• A. It measures peak levels in impulse noise.
• B. It calibrates microphones for outdoor measurement.
• C. It approximates the equal loudness curve and the ear response to various frequencies.
• D. It averages sound over time.

Answer: (C)

A-weighting is a frequency weighting that adjusts sound pressure to reflect how we actually hear sounds. The human ear is not equally sensitive to all frequencies, being most sensitive in the mid range (roughly 2–4 kHz) and less sensitive to very low and very high frequencies. A-weighting applies a filter that boosts those mid frequencies and attenuates the extremes, so the resulting dBA value tracks perceived loudness rather than raw energy. This makes dBA readings align better with occupational hearing risk and annoyance considerations. It’s not about measuring peak impulse levels, microphone calibration for outdoor measurements, or time averaging—that part is handled separately—so the idea that it approximates the ear’s equal-loudness response across frequencies is why this is the best description.