Combined outer and middle ear amplification spans roughly 600 to 4000 Hz

Evidence

The transfer function of the outer ear shows only a small amount of gain below 1000 Hz, and the amount of gain increases with increasing frequency until it peaks at approximately 2500 Hz. The middle ear shows a broader response, with the most gain around 800 Hz. The heavy, solid line illustrates the combined response of the outer and middle ears. The combined transfer function demonstrates that the outer and middle ear, together, provide amplification over a wide range of frequencies, between roughly 600 and 4000 Hz. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 214

Categorization

• XREF: This amplification range corresponds to the most critical frequencies for speech perception, a useful bridge to hearing-aid fitting practice.