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Outer ear canal resonance explains peak sensitivity near 4 kHz

Properties2
tagsja-picks, define, xref, causal_relationships, trade, corroborated, category/causal-relationships
aliases@heller_why_2013, loc. 2005

4 min read

Outer ear canal resonance explains peak sensitivity near 4 kHz

Evidence

The dip around 3400 Hz (a dip means we are more sensitive to sound there—it requires a lower SPL to detect a sound) is due to an outer ear phenomenon: a resonance of the tube (auditory meatus) leading out from the tympanum. The meatus is about 25 mm long and is open at one end. The first resonance of a half-open tube is at frequency f = c/4L = 343/0.01 = 3430 Hz, a very good match to the dip. The resonance makes sounds in the 3400 Hz frequency range louder, lowering the threshold an external sound source needs to reach to become audible. — Eric J. Heller, Why You Hear What You Hear- An…, 2005

The first is that there are some humps and bumps in the contours above 1 kHz. These are due to the resonances of the outer ear. Within the outer ear, there is a tube about 25 mm long with one open and one closed end. This will have a first resonance at about 3.4 kHz and, due to its nonuniform shape, a second resonance at approximately 13 kHz, as shown in the figure. The effect of these resonances is to enhance the sensitivity of the ear around the resonant frequencies. Note that because this enhancement is due to an acoustic effect in the outer ear, it is independent of signal level. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 624

The first is that there are some humps and bumps in the contours above 1 kHz. These are due to the resonances of the outer ear. Within the outer ear there is a tube about 25 mm long with one open and one closed end. This will have a first resonance at about 3.4 kHz and, due to its non-uni­ form shape, a second resonance at approximately 13 kHz, as shown in the figure. The effect of these resonances is to enhance the sensitivity of the ear around the resonant frequencies. Note that because this enhancement is due to an acoustic effect in the outer ear it is independent of signal level. — David Howard, Jamie Angus, coustics and Psychoacoustics, 613

Within the outer ear, there is a tube about 25 mm long with one open and one closed end. This will have a first resonance at about 3.4 kHz and, due to its nonuniform shape, a second resonance at approximately 13 kHz, as shown in the figure. The effect of these resonances is to enhance the sensitivity of the ear around the resonant frequencies. Note that because this enhancement is due to an acoustic effect in the outer ear, it is independent of signal level. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 624

Categorization

  • DEFINE: Explains the auditory meatus as a half-open tube and derives its first resonance frequency.
  • XREF: Physically grounded mechanism connects to why headphones and ear-canal acoustics matter in recording and reproduction; ties into acoustic resonance of tubes. — connects to: Hearing damage first appears at the ear canal’s resonance frequency near 4 kHz — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 677; The ear canal acts as a quarter-wavelength resonator amplifying 3-4 kHz by 10 dB — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 728; Outer and middle ear structures provide frequency-specific amplification of incoming sound — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 212 (+4 more)
  • corroborated: 6 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 2005; David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 624; David Howard, Jamie Angus, coustics and Psychoacoustics, 613

Broader Connections

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