Why do 500 and 1000 Hz have lower allowable ambient noise levels in screening?

Why do 500 and 1000 Hz have lower allowable ambient noise levels in screening?

• A. Because high-frequency noise is more distracting
• B. Because of upward spread of masking/excitation
• C. Because 500/1000 Hz are not important
• D. Because equipment is less sensitive at those frequencies

Answer: (B)

Masking in the auditory system is asymmetric: energy from lower frequencies can cause excitation that spreads upward in frequency on the basilar membrane, masking higher-frequency tones more than the reverse. Because 500 and 1000 Hz sit in the mid-frequency range used for screening, any ambient noise energy in the lower part of the spectrum can raise the audible threshold for these tones. To obtain accurate, reliable screening results, the room’s noise floor must be kept very low at these frequencies, preventing masking from surrounding low-frequency noise. That’s why the answer hinges on the upward spread of masking.

Masking in the auditory system is asymmetric: energy from lower frequencies can cause excitation that spreads upward in frequency on the basilar membrane, masking higher-frequency tones more than the reverse. Because 500 and 1000 Hz sit in the mid-frequency range used for screening, any ambient noise energy in the lower part of the spectrum can raise the audible threshold for these tones. To obtain accurate, reliable screening results, the room’s noise floor must be kept very low at these frequencies, preventing masking from surrounding low-frequency noise. That’s why the answer hinges on the upward spread of masking.