Earbud Test — Seal & Balance Check

An earbud test checks the two things that decide how in-ear headphones sound: the seal in your ear canal and the balance between the two drivers. It alternates a 50 Hz sub-bass tone with a 500 Hz reference, then steps tones from 125 Hz to 8 kHz to check the phantom centre. Everything runs in your browser; nothing is uploaded.

How to use it

1. Start on the seal tab. The first tab is “1. Acoustic Canal Seal & Bass Loss”. Fit the buds as you normally wear them, with the tips you intend to use.
2. Press Play Alternating Tones. A 50 Hz sub-bass tone plays for 1.5 seconds, then a 500 Hz reference for 1.5 seconds, repeating. The sub tone is generated about 9.5 dB hotter to compensate for the ear’s low-frequency sensitivity.
3. Compare the two tones, not their loudness. If both sound full, the tip is sealing. If the 500 Hz tone is clear while the 50 Hz tone is thin, air is leaking past the tip.
4. Repeat one tone if you need to. Press “50 Hz Sub-Bass Only” or “500 Hz Reference Only” to hold a tone while you adjust the fit.
5. Run the push test. With the 50 Hz tone playing, gently press the buds inward. If bass suddenly appears, the tip is too small or not inserted deep enough.
6. Check balance on the second tab. On “2. Channel Balance & Wax Check”, choose 125, 250, 500, 1000, 2000, 4000, or 8000 Hz and press Play. Each tone is a centred mono sine at 0.25 gain, so a matched pair images in the centre.

Why the seal decides the bass

An in-ear driver works into a closed chamber: the volume between the tip and your eardrum is roughly 1 cm³, about the size of a small marble, and the tip is what closes it. A leak turns that chamber into an acoustic shunt, and at 50 Hz the pressure changes slowly enough for air to escape, so the canal behaves like a high-pass filter. Measured response below 200 Hz commonly falls by several dB, and a badly fitted tip can lose more than 10 dB, which is why weak earbud bass is almost always a fit problem.

The 500 Hz reference is largely immune to the same leak because its pressure alternates too quickly for the gap to equalise it. That is what makes the pair useful: one frequency tests the seal, the other confirms the driver still works. If the 500 Hz tone is missing too, the problem is upstream of the fit.

The canal itself has a resonance: a roughly 2.5 cm tube open at one end peaks near 343 / (4 × 0.025) ≈ 3.4 kHz, and that boost is part of why in-ears sound detailed in the presence region. Insertion depth changes the effective length, so deeper tips push the resonance up and can brighten the treble.

Channel balance, wax and the phantom centre

The balance tab steps through seven octave tones, 125 Hz to 8 kHz, each identical in both ears. A matched pair keeps the image locked in the centre, and 1 to 2 dB of level difference pulls it toward the louder side.

Compacted earwax and clogged nozzle mesh block short wavelengths first: 8 kHz has a wavelength of about 4.3 cm, small enough to be scattered by debris in the nozzle, while 125 Hz measures 2.74 m and passes through largely unaffected. A wax problem therefore shows up as an 8 kHz tone that leans to one side while the bass stays centred.

Tone	Wavelength in air (343 m/s)	What a one-sided drop suggests	What to try
125 Hz	2.74 m	Tip seal on that ear	Reseat or upsize the tip
250 Hz	1.37 m	Seal or canal asymmetry	Try the tip size from the other ear
500 Hz	0.69 m	Nozzle mesh partly blocked	Clean the mesh
1 kHz	0.343 m	Driver or mesh	Swap buds between ears to confirm
2 kHz	0.17 m	Wax or mesh	Clean, then retest
4 kHz	0.086 m	Wax or nozzle	Clean, then retest
8 kHz	0.043 m	Wax or mesh clogging	Clean, then retest

The swap test separates hardware from hearing. If the quiet side follows the bud when you trade them between ears, the bud is the problem. If it stays with the same ear whichever bud is in it, the cause is on your side of the tip: wax, canal shape, or a hearing difference. If a consistent difference persists across tools and after cleaning, and you are concerned, see an audiologist.

Accuracy, limits and troubleshooting

• This is a listening test, not a measurement. The page has no microphone and no level meter, so it cannot plot a frequency response; it tells you whether a seal exists and whether the sides match.
• Keep the volume fixed and low. Compare tones by character rather than loudness; raising the volume mid-test defeats the comparison.
• Bluetooth processing can add its own imbalance. A2DP sends both channels together, but true wireless sets with independent per-ear processing can drift; re-pair, then retest, and test wired if you can.
• Noise cancelling changes the response. Run the checks with ANC off, then repeat with it on to hear the difference.
• Operating-system settings matter. Mono audio folds both channels together, volume limiters compress the top of the range, and spatial audio re-renders stereo. Disable all three.
• Tips change the result. Foam expands to fill the canal and often seals better, at the cost of a little treble; silicone is quicker to fit. Clean the nozzle mesh gently with a dry tool, never the canal.
• Burn-in will not change the sound. A soak run can confirm the drivers keep working, but no controlled listening test has shown a sound-quality benefit.
• A consistent one-sided loss is a screening signal, not a diagnosis. If you are concerned, see an audiologist.

Related tools

• Headphone Test — Channel isolation, driver matching, and an ITD demo for over-ear and on-ear models.
• Headphone Burn-In Test — A time-boxed soak run with a countdown if you want to confirm driver stability.
• Frequency Check — A quick sweep-based check of which frequencies you can hear on each side.