Tympanometer Product

Overview

A tympanometer is an audiological instrument that measures how stiff or compliant (floppy) the eardrum and middle ear are by applying a small air pressure to the ear canal while playing a low-frequency test tone. The device measures how much of the tone is reflected back by the eardrum versus how much is absorbed by the middle ear. A healthy eardrum reflects a typical amount at a normal middle ear pressure; a stiff eardrum (from ear wax, fluid behind the drum, or otosclerosis) reflects more; and a flaccid eardrum (from a perforation or ossicular discontinuity) reflects less. The resulting graph, called a tympanogram, is a unique diagnostic fingerprint that lets an audiologist identify middle ear dysfunction in seconds without any subjective response from the patient—making it invaluable in newborn hearing screening, pediatric assessment, and objective documentation of ear health.

The Probe Headset Assembly inserts into the ear canal, creating an airtight seal. The Tone Generator Speaker emits a continuous 226 Hz test tone, and the Probe Microphone listens for the echo. Simultaneously, the Pressure Pump & Valve sweeps the air pressure from negative to positive daPa (decapascals, a unit of pressure equal to 0.1 pascal). At each pressure step, the processor measures the intensity of the returned tone and calculates the admittance (how much sound is absorbed). The resulting curve—admittance plotted against pressure—is the tympanogram.

How it works

The Probe Headset Assembly contains three channels: one delivers the 226 Hz test tone from the Tone Generator Speaker, one returns the reflected sound to the Probe Microphone, and one connects to the Pressure Pump & Valve to apply pressure. When the probe seals the ear canal, the entire canal volume becomes a closed acoustic system. The test tone travels down the canal, strikes the tympanum, and some of it bounces back. How much bounces back depends on the compliance of the eardrum and the pressure in the middle ear space behind it.

The Pressure Pump & Valve is controlled by the Signal Processing Unit, which commands the Small Air Pump Motor to pressurize the canal. Typically, the pressure starts at -600 daPa (a partial vacuum) and ramps up to +200 daPa at a rate of 50 daPa/second. At each pressure point, the processor collects data from the microphone and calculates acoustic admittance (Y), measured in millimhos (mmho, or millisiemens), which is the inverse of impedance. Admittance increases as the eardrum becomes more compliant; it peaks when the eardrum is most compliant, which normally occurs near zero daPa (atmospheric pressure in the middle ear).

The Signal Processing Unit performs a running spectral analysis: it compares the amplitude and phase of the returned 226 Hz tone to the reference (the outgoing tone). From this comparison, it extracts the absorbance of that frequency. Modern tympanometers often measure not just the 226 Hz admittance but also higher frequencies (typically 1000 Hz) to improve diagnostic sensitivity for certain middle ear pathologies. The multi-frequency approach is called wideband tympanometry.

Three key measurements define the tympanogram:

1. Peak compliance or admittance (Ytm or Ca): how much the middle ear absorbs at its most compliant point
2. Middle ear pressure (Pm or Me): the pressure at which peak compliance occurs
3. Ear canal volume (V or Vea): the air in the canal itself

These are interpreted using a simple classification system (Types A, B, C, As, Ad) that lets an audiologist immediately recognize common pathologies:

• Type A: Normal (peak near 0 daPa, compliance 0.3–1.5 mmho)
• Type As: Stiff middle ear (shallow peak, normal pressure)—suggests otosclerosis or ossicular fixation
• Type Ad: Flaccid eardrum (very tall peak)—suggests ossicular discontinuity
• Type B: Flat tympanogram—suggests fluid behind eardrum or TM perforation
• Type C: Normal compliance but negative pressure—suggests Eustachian tube dysfunction

The Display & Control Console plots the tympanogram curve in real time as the pressure is swept. Once the curve is complete (usually within 5 seconds), the Thermal Printer automatically prints the results on thermal paper, or the data is transmitted via USB to an electronic health record. The Signal Processing Unit labels the curve with type classification and numerical values.

Calibration uses Calibration Cavity Set sealed cavities of known compliance: a 1 mL cavity (very stiff, used to check the low end) and a 5 mL cavity (very compliant, checking the high end). Each day before clinical use, the probe is attached to these calibration cavities and a test run is performed. The results should match stored reference values; if they drift, the system alerts the operator and may lock out testing until recalibration.

The entire measurement is objective: it requires no behavioral response from the patient, making it especially valuable in pediatric populations (infants and toddlers) and patients who cannot communicate reliably (developmentally delayed, comatose, or non-verbal individuals). Newborn hearing screening protocols routinely use tympanometry to rule out conductive hearing loss (which would affect behavioral thresholds) and identify middle ear pathology that could explain a failed screening.