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Appliance Hum Detector

Point your microphone at a buzzing appliance and this tool finds the electrical mains hum — the 50 Hz or 60 Hz fundamental and its harmonics (100/120, 150/180, 200/240 Hz…) — shows them on a live low-frequency spectrum, tells you which mains region dominates, and offers a best-guess at the source with things to try.

⚠ The frequency detection is reliable and calibration-independent — where the peaks sit (50 vs 60 Hz, which harmonics are strong, before/after with the same mic) is genuinely meaningful. The source attribution is a heuristic best guess, not a diagnosis. The level is shown as relative dBFS from an uncalibrated consumer mic, which also generally cannot capture true infrasound; an SPL figure only appears if you calibrate, and it is still an estimate — never legal or compliance evidence. Audio is analysed live and is never recorded or uploaded.

Microphone

Starting asks for microphone permission. Automatic gain, noise suppression and echo cancellation are requested off so the hum reads truthfully — most browsers honor this, though some operating systems may override it. Audio is analysed in your browser only and never recorded, saved, or transmitted.

Idle — press Start, then hold the mic close to the suspected appliance.
Detected hum
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Start the mic to detect a 50 Hz or 60 Hz mains tone.
Overall level
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Relative dBFS from an uncalibrated mic. Use it for before/after comparisons.
How to read this
Move the mic right up to one device at a time and watch which makes the orange peaks grow — that change is the reliable clue.

Harmonic family

Harmonics will be listed here once a 50 Hz or 60 Hz hum is detected.

Likely source (heuristic best guess)

Detect a hum to see a heuristic best guess at its source. The guess is not a diagnosis.
⚠ The source guess is inferred only from the shape of the harmonics a consumer mic picks up. Many sources overlap, and a ground loop in your audio chain will not even be in the room air. Treat it as a starting point and confirm by switching devices off one at a time.

Optional: estimate dB SPL (shared calibration)

Live level now
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Not calibrated.
Idle.

How It Works

Electricity in your home alternates at the mains frequency — 50 Hz in most of Europe, Africa, Asia and Oceania, and 60 Hz across the Americas and parts of Asia. Anything that vibrates in step with that current radiates sound at that frequency and at its harmonics. Transformer and motor laminations are pulled twice per cycle (the force does not care about the current’s direction), so they hum loudest at twice the mains frequency: 100 Hz on a 50 Hz grid, 120 Hz on a 60 Hz grid. Other components add a ladder of higher harmonics — 150/180, 200/240 Hz and up — and the pattern of those harmonics is what gives a hum its character.

This tool runs a high-resolution FFT on your microphone signal and measures how far the bins at 50× and 60× their harmonics rise above the surrounding noise floor. Whichever family (50 Hz or 60 Hz) has the greater total prominence wins, telling you the mains region. It then flags which harmonics are strong and draws them as orange lines on the live spectrum so you can see the hum directly. Because this is pure frequency analysis, it is calibration-independent: the peak positions and the 50-vs-60 verdict do not depend on how loud or sensitive your mic is.

From the harmonic shape it offers a heuristic guess at the source: a dominant second harmonic suggests a transformer or power supply; energy spread across many upper harmonics suggests a fluorescent/LED ballast or dimmer; a strong fundamental with some upper-harmonic energy suggests a motor; and a strong low-order line with weak upper harmonics, especially heard through audio gear, suggests a ground loop — note that ground-loop hum is frequently strongest at the second harmonic (100 Hz on a 50 Hz grid, 120 Hz on 60 Hz) because the heavy ground currents come from rectifier power supplies, not only at the fundamental. This is a best guess, not a measurement — sources overlap and real rooms are messy — so confirm it by turning suspects off one at a time and watching the peaks. The optional calibration only affects the loudness estimate (a shared offset used across all of our noise tools); it never changes the frequencies.

Frequently Asked Questions

How does it tell 50 Hz hum from 60 Hz hum?
It runs a high-resolution FFT and measures how far the peaks at the 50 Hz family (50, 100, 150…) and the 60 Hz family (60, 120, 180…) rise above the surrounding noise floor. The family with the greater total prominence wins. This is pure frequency detection, so it is reliable and does not depend on calibration — though if 50 and 60 Hz are very close in strength the tool says so rather than guessing.
Why is the 100 or 120 Hz harmonic often louder than the fundamental?
Magnetic forces in transformers and motors pull the metal twice per electrical cycle, because the force does not care which way the current flows. That makes the dominant mechanical hum appear at twice the mains frequency — 100 Hz on a 50 Hz grid or 120 Hz on a 60 Hz grid — so the second harmonic is frequently the strongest line, a clue that often points at a transformer or power supply. A dominant second harmonic is not exclusive to transformers, though: ground-loop hum is also frequently strongest at 100/120 Hz, because the heavy ground currents that cause it come from rectifier power supplies rather than the 50/60 Hz fundamental.
Can I trust the “likely source” it names?
Treat it as a heuristic best guess, not a diagnosis. It is inferred only from the shape of the harmonics your microphone picks up, and many real sources overlap or sound similar. A ground loop, in particular, lives in your audio wiring and may not be in the room air at all. Confirm by switching suspected devices off one at a time and watching whether the peaks drop.
Is the loudness reading a real decibel measurement?
No. A browser microphone is uncalibrated, so the level is shown as relative dBFS, not certified dB SPL. It is useful for before/after comparisons with the same mic and setup. If you enter a reading from a real sound-level meter the tool stores a shared offset and shows an SPL estimate, but that is still an estimate — never use it as legal, complaint, or compliance evidence.
It detects nothing even though I can hear a hum — why?
Move the microphone much closer to the appliance, and keep voices, music and other sounds quiet during the reading. Make sure your browser is using this tool’s raw microphone settings (automatic gain and noise suppression are requested off, because they would mangle the hum — if your OS forces them you may need to disable microphone enhancements in system settings). Some very low rumble is true infrasound below about 20 Hz that consumer mics simply cannot capture, and a faint ground-loop hum may be inside cables rather than in the air.
Is my audio recorded or uploaded?
No. The microphone signal is analysed in real time entirely inside your browser to find the hum, and is never recorded, saved, or transmitted. The microphone connects only to an analyser node, never to your speakers, and it is released the moment you press Stop or close the tab.

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