Speaker & Earphone Balance + Frequency Sweep Test

About Speaker & Earphone Balance + Frequency Sweep Test

Every sound is synthesized on the spot with the browser's Web Audio API. Nothing is a recording, so sweep frequencies are exact, and choosing "Left" sends a gain of zero, true digital silence, to the right channel. If you still hear something on the right, the cause is on the playback side: mono audio, spatial audio or a crossfeed setting.

Volume starts at 14%, about -17 dBFS. A pure sine sounds much louder than music at the same setting, and near-inaudible tones around 20 kHz tempt people to turn the volume up. Tweeters and ears take the energy whether you hear it or not.

What a left/right check actually catches

Swapped channels are more common than you would think: speaker wires crossed at the back of an amplifier, earbuds in the wrong ears, studio monitors with their L and R inputs reversed. If "Left" comes out on the right, check the wiring. If it comes out of both sides equally, check for a mono audio setting first: Windows has one under Accessibility, and iOS and macOS both call it Mono Audio.

The fine balance slider uses an equal-power pan law. At center each side gets cos 45° ≈ 0.707 gain, or -3 dB, so total power stays constant as you move to either side. If the center position sounds off to one side, nudge the slider the other way until the image sits in the middle. That offset is your system's imbalance. Pink noise works better than a sine wave for this. A single sine tone easily creates spots in a room where reflections make it louder in one ear.

With Bluetooth earphones, the auto-alternate switch may lag a little because of codec buffering. That is not a fault.

20 Hz to 20 kHz, and age

Human hearing is usually quoted as 20 Hz to 20 kHz, but that is an idealized young ear. Age-related hearing loss (presbycusis) comes from wear on the hair cells of the inner ear and takes the high frequencies first. The US National Institute on Aging says about one in three adults aged 65 to 74 has hearing loss. It is not unusual for people in their twenties to hear nothing above 15 or 16 kHz.

So if the sweep fades out around 14 kHz, this page alone cannot tell you whether it is the speaker or your ears. Have someone else listen from the same spot, or play the same headphones from a different device. This is not a hearing test: a real audiogram measures thresholds at each frequency with calibrated headphones in a quiet room. Do not judge your hearing from the highest tone you can hear here.

At the low end the speaker usually gives out first. Laptop speakers produce almost nothing below a few hundred hertz, and around 20 Hz you feel a large subwoofer more than you hear it. When you sweep up from 20 Hz, the frequency where the tone suddenly "appears" is roughly that speaker's bass limit.

Boom at one note, silence at another: room modes

Between two parallel walls, standing waves form at frequencies where twice the wall spacing is a whole number of wavelengths. The axial mode frequencies are f = n × 343 / (2 × length). At those frequencies the level swings wildly with position: huge in one spot, nearly gone a meter away. If one bass note makes the whole room hum during a sweep, or moving your chair changes the bass, you are hearing the room, not the speaker.

The wavelength readout uses 343 m/s. At 50 Hz the wavelength is 6.86 m, comparable to the room, which is why modes dominate the bass. At 1 kHz it is 34 cm and at 10 kHz 3.4 cm, so treble depends more on where the speaker is pointed (high frequencies drop off quickly off-axis) than on the room.

A buzz or rattle at one frequency is usually a grille, cabinet panel or object on the desk resonating. Hold that frequency with the manual tone and press on things one at a time until the rattle stops.

Log vs. linear sweep

The default log sweep spends the same time on every octave. 20 Hz to 20 kHz is a factor of 1,000, about 9.97 octaves, so a 12-second sweep spends roughly 1.2 seconds per octave. A linear sweep spends the same time on every hertz: all the bass flashes by in under a second and the rest is treble. Pitch perception is close to logarithmic, which is why the log sweep sounds like an even climb.

Worked examples

How to use it

1. Start with the volume low, and hold earphones slightly away from your ears at first.
2. Play left and right separately, then check that "Both" images in the center.
3. Run a sweep and note where the bass appears, where the treble vanishes and where anything rattles.
4. Hold any suspect frequency with the manual tone to track down the cause.

Frequently asked questions