Wideband & Multi-Frequency Tympanometry

Beyond the 226 Hz probe tone: multi-frequency tympanometry, wideband absorbance, and the resonance frequency.

Conventional tympanometry uses a single low-frequency probe tone — usually 226 Hz — and works well for the everyday question of whether the middle ear is sealed, aerated and mobile. But a single low frequency only sees one slice of a system whose behaviour is strongly frequency-dependent. Two ears with identical 226 Hz tympanograms can transmit sound very differently across the rest of the spectrum. [Hunter LL 2013]

From one probe tone to many

Multi-frequency tympanometry extends the measurement by sweeping pressure at several probe frequencies — 226, 678, 800 and 1000 Hz are commonly reported together. Higher probe frequencies are more sensitive to changes in the mass and stiffness of the ossicular system, which is why a 1000 Hz probe tone is the standard for infants, whose highly compliant ear canals make a 226 Hz trace unreliable. [Hunter LL 2013][Hunter LL 2013]

The 1000 Hz trace does not look like the familiar 226 Hz peak. In many ears it is more complex and can show a double peak, so its interpretation is less a matter of reading a single peak height and more a matter of recognising a shape. [Hunter LL 2013]

Wideband acoustic immittance

Wideband acoustic immittance — also called wideband absorbance or wideband tympanometry — goes further again. Instead of pure tones it uses a brief click, which contains energy across a broad band, commonly 226 Hz to 8 kHz. The instrument reports how much of that energy the middle ear absorbs at each frequency. Absorbance is a fraction between 0 (all energy reflected) and 1 (all energy absorbed); the reflected fraction is the mirror-image reflectance. [Keefe DH 1993][Hunter LL 2013]

Because a wideband measurement can be made at ambient pressure and at the tympanometric peak pressure, and across the whole frequency range at once, it builds a far richer picture of middle-ear function in the same time a conventional tympanogram takes. [Hunter LL 2013]

The normal absorbance pattern

In a normal adult ear, absorbance is low at low frequencies — the stiffness-controlled region reflects most of the energy — then rises to a broad peak through the mid frequencies before falling away again at the high end. The frequency at which the stiffness and mass elements of the middle ear are balanced is the resonance frequency, and it sits near the absorbance peak — around 900 Hz in normal adult ears. [Keefe DH 1993][Karuppannan A 2021]

Why it matters: stiffness versus mass

The resonance frequency moves in a clinically meaningful direction. Anything that stiffens the system shifts resonance higher: group studies of otosclerosis report resonance frequencies well above the normal range, around 1400 Hz, with reduced low-frequency absorbance. Anything that adds mass or loosens the system shifts resonance lower: ossicular discontinuity has been reported with resonance frequencies around 670–750 Hz and raised low-frequency absorbance. [Karuppannan A 2021]

This is the real payoff of the wideband approach. Otosclerosis and ossicular discontinuity can both present with a conductive loss, and on a 226 Hz tympanogram the distinction rests largely on peak height. The wideband absorbance pattern and the resonance frequency separate them more directly — one is a stiffness problem, the other a mass problem, and the curve shows which. [Karuppannan A 2021][Hunter LL 2013]

Middle-ear effusion, by contrast, damps the system broadly: wideband absorbance is reduced across a wide span of frequencies, and studies using higher probe frequencies and wideband measures report improved sensitivity for detecting effusion compared with the 226 Hz tympanogram alone. [Hunter LL 2013][Onusko E 2004]

Wideband immittance is still maturing as a routine clinical tool, and interpretation is less standardised than the Jerger types. But as an addition to the battery — quick, objective, and richer than a single probe tone — it is increasingly part of how the middle ear is assessed. Use the explorer below to see how the absorbance curve and the resonance frequency move with stiffness and mass. [Hunter LL 2013]

Wideband absorbance explorer

Shape an absorbance curve with the sliders and watch the resonance frequency move. Stiffen the system and resonance rises; add mass or loosen it and resonance falls. Overlay a disease signature to compare.