An audiometer attenuator is set to 0 dB HL. Which statement about the sound-pressure level output at the earphone is true?

An audiometer attenuator is set to 0 dB HL. Which statement about the sound-pressure level output at the earphone is true?

• A. It is constant across all frequencies.
• B. It is lowest at midfrequencies.
• C. It increases as a function of frequency.
• D. It is highest at 4000 Hz.

Answer: (B)

The key idea is that 0 dB HL is a reference to the average normal-hearing threshold at each frequency, not a fixed SPL. Because the ear’s sensitivity varies with frequency, the actual sound pressure level at the earphone needed to reach 0 dB HL also varies. The human ear is most sensitive in the midfrequency range, so the SPL required to achieve 0 dB HL is smallest there. At the low and high ends, thresholds are higher in SPL, so more SPL is needed. Thus, when the attenuator is set to 0 dB HL, the earphone’s output SPL is lowest at midfrequencies.

The key idea is that 0 dB HL is a reference to the average normal-hearing threshold at each frequency, not a fixed SPL. Because the ear’s sensitivity varies with frequency, the actual sound pressure level at the earphone needed to reach 0 dB HL also varies. The human ear is most sensitive in the midfrequency range, so the SPL required to achieve 0 dB HL is smallest there. At the low and high ends, thresholds are higher in SPL, so more SPL is needed. Thus, when the attenuator is set to 0 dB HL, the earphone’s output SPL is lowest at midfrequencies.