An audiometer delivers precise tones through headphones or a bone vibrator, one frequency at a time, to find the softest sound a person can hear at least 50% of the time. That softest detectable level, measured in decibels, is the hearing threshold. The entire process follows a standardized method that keeps results reliable and comparable across clinics, workplaces, and screening programs.
Setting Up the Testing Environment
Background noise is the biggest threat to accurate results. Even moderate ambient sound can mask the quiet tones you’re trying to measure, artificially inflating someone’s thresholds. The U.S. standard (ANSI S3.1) sets maximum permissible ambient noise levels for test rooms, and they’re strict: at 500 Hz, background noise must stay below about 19.5 dB when the person wears headphones, and below 14.5 dB when ears are uncovered. In practical terms, this means testing should happen inside a sound-treated booth or, at minimum, a very quiet room with the door closed and no HVAC noise blowing nearby.
Before each session, check that the audiometer has been calibrated according to the manufacturer’s schedule. Calibration ensures that a tone labeled “25 dB at 1000 Hz” actually delivers exactly that. Most clinical audiometers require annual electroacoustic calibration plus a daily listening check, where the tester puts on the headphones and runs through each frequency to confirm the equipment sounds normal and balanced.
Choosing and Placing Transducers
Audiometers use three main types of transducers, each serving a different purpose.
- Supra-aural headphones sit on top of the outer ear. These are the traditional cushioned headphones most people picture during a hearing test. They’re reliable for standard frequencies (250 to 8000 Hz) but can collapse a narrow ear canal if pressed too firmly.
- Insert earphones use a small foam tip placed directly into the ear canal. They reduce background noise more effectively than supra-aural headphones, avoid ear canal collapse, and increase the isolation between ears, which reduces the need for masking.
- Bone conduction oscillator is a small vibrating device placed on the mastoid bone, the bony bump just behind the ear. It bypasses the outer and middle ear entirely and sends vibrations directly to the inner ear. This tells you whether a hearing loss originates in the outer/middle ear or the inner ear itself.
For supra-aural headphones, center the speaker opening directly over the ear canal. For insert earphones, compress the foam tip, slide it into the canal, and hold it briefly while it expands for a snug seal. For the bone oscillator, place it on the most prominent part of the mastoid where the skin is thinnest. A standard steel headband holds it in place. Make sure it sits firmly against the bone with no hair trapped underneath, since hair reduces vibration transfer.
Instructing the Person Being Tested
Clear instructions before you start prevent confusion and false responses. A standard script goes something like this: “You are going to hear a series of tones or beeps through the headset. Your job is to raise your hand (or press the button, or say ‘yes’) each time you hear a tone. Some of the tones will be easy to hear and others will be very soft or quiet. Respond even if the tone sounds very faint or far away.”
Keep the instructions simple and confirm the person understands before proceeding. If you’re also doing bone conduction testing, the instructions are the same. The person responds to any tone they hear, regardless of how the sound reaches them.
The Frequency Sequence
Start with the person’s better ear. If they don’t notice a difference between ears, default to the right ear first. The standard frequency sequence for each ear follows a specific order designed to check reliability along the way:
Begin at 1000 Hz, then drop to 500 Hz, then retest 1000 Hz. If the first and second 1000 Hz thresholds agree within 5 dB of each other, continue upward through 2000, 3000, 4000, 6000, and 8000 Hz. If they don’t agree, repeat 1000 Hz until you get two consistent results. This retest acts as a built-in reliability check. Once the first ear is done, switch to the other ear and run through the full sequence: 1000, 500, 2000, 3000, 4000, 6000, and 8000 Hz.
Clinical testing sometimes extends the range down to 125 or 250 Hz and includes half-octave frequencies like 750 and 1500 Hz. Occupational hearing conservation programs typically test only 500 through 8000 Hz.
Finding the Threshold: The Up-Down Method
The standard technique for finding each threshold is called the modified Hughson-Westlake method. It uses a “down 10, up 5” pattern that zeroes in on the quietest level the person can detect.
Start by presenting a tone at a level you expect the person to hear easily, often around 30 or 40 dB. If they respond, drop the level by 10 dB. Keep dropping by 10 dB each time they respond until they stop responding. That means you’ve gone below their threshold. Now increase by 5 dB. If they respond, drop 10 dB again. If they don’t respond, go up another 5 dB. Continue this bracketing pattern. The threshold is the lowest level at which the person responds at least two out of three times on ascending presentations (getting louder). In other words, you’re looking for the level where they can detect the tone at least half the time, confirmed by repeated ascending trials.
This entire sequence typically takes under a minute per frequency once you’re practiced. For a full bilateral air conduction test across seven frequencies per ear, expect 15 to 20 minutes.
Adding Bone Conduction Testing
After air conduction testing, bone conduction reveals whether a hearing loss involves the outer and middle ear (conductive loss), the inner ear (sensorineural loss), or both (mixed loss). Place the bone oscillator on the mastoid of the ear you’re testing and follow the same up-down threshold procedure, typically testing at 250, 500, 1000, 2000, and 4000 Hz.
If bone conduction thresholds are normal but air conduction thresholds are elevated, the problem lies in the outer or middle ear. If both are equally reduced, the inner ear or hearing nerve is involved. A gap between the two, called an air-bone gap, is the hallmark of conductive hearing loss.
One complication with bone conduction: vibrations travel through the skull and can stimulate both inner ears simultaneously. When there’s a significant difference in hearing between the two ears, you may need to apply masking noise to the non-test ear through its headphone to prevent it from “hearing” the tone meant for the other ear. Masking is a more advanced skill, but the principle is straightforward: you’re using controlled noise to keep the better ear busy so it doesn’t interfere.
Recording Results on the Audiogram
An audiogram plots frequency (pitch) on the horizontal axis and intensity (loudness) on the vertical axis, with softer sounds at the top and louder sounds at the bottom. Each threshold you find gets plotted using standardized symbols:
- Right ear air conduction (unmasked): red circle (O)
- Left ear air conduction (unmasked): blue X
- Bone conduction (unmasked): angle brackets, sometimes shown as chevrons or circumflex accents
- Masked bone conduction: square brackets ([ for left, ] for right)
Red is always right, blue is always left. Connect the circles for the right ear with a red line and the Xs for the left ear with a blue line. Normal hearing falls between 0 and 25 dB across all frequencies. Thresholds of 26 to 40 dB indicate mild loss, 41 to 55 dB moderate loss, and anything above 70 dB severe to profound loss.
Common Mistakes to Avoid
Rhythm is the most frequent source of false responses. If you present tones at regular intervals, the person starts anticipating and may respond to silence. Vary the time between tone presentations randomly, somewhere between one and three seconds, to keep the test honest.
Tone duration matters too. Present each tone for one to two seconds. Tones that are too brief may be missed by someone with normal hearing, and tones that are too long waste time and blur the response.
Watch for collapsing ear canals with supra-aural headphones, especially in older adults. If thresholds at higher frequencies seem unusually poor and the ear canal is narrow or soft, switching to insert earphones often solves the problem immediately. Also check that earphone placement hasn’t shifted during the test, particularly if results seem inconsistent on one side.
Finally, don’t skip the 1000 Hz retest. That 5 dB reliability check is your early warning that the person understands the task and is responding consistently. If you can’t get two results within 5 dB at 1000 Hz, re-instruct and start over rather than pushing forward with unreliable data.