Vibration Spectrum Comparator
Capture a baseline spectrum of a running machine, then later capture a current reading with the same microphone and gain. The tool overlays the two 1/3-octave spectra, color-highlights the frequency bands where the level rose, and lists them largest-first so you can match them against your calculated bearing, gear-mesh, imbalance or blade-pass frequencies. Save named baselines to your browser to trend a machine across sessions, watch specific fault frequencies over time, and export an annotated comparison report.
⚠ This microphone hears AIRBORNE SOUND, not accelerometer vibration. It reveals the frequency content of the sound your machine radiates — genuinely useful for spotting which tones grew — but it is not a calibrated vibration measurement: the absolute level is uncalibrated and is not in mm/s velocity or g acceleration, and this is not an ISO 10816 / ISO 2372 severity assessment (those need a calibrated accelerometer). The trustworthy part is the difference between two captures: with the same mic and gain the unknown calibration offset cancels, so “this band rose +9 dB” is reliable. For real vibration measurement use an accelerometer + analyzer. Auto-gain and noise suppression are requested off. Nothing is recorded or uploaded.
Keep the microphone in the same spot, at the same distance, and don’t touch the input gain between captures — that’s what makes the comparison valid. The microphone is connected to the analyzer only; it is never played back.
| Metric | Baseline | Current |
|---|---|---|
| Overall level | — | — |
| Peak sample | — | — |
| Dominant bands | — | — |
| Clips | — | — |
Capture both a Baseline and a Current reading to see which frequency bands increased.
Saved baselines — trend a machine across sessions
Save your current Baseline capture under a name (e.g. a machine ID), then on a later day load it back and capture a fresh Current reading to see what changed. Baselines are stored only in this browser’s local storage — nothing is uploaded.
Watch frequencies — track specific fault tones
Add the exact frequencies you care about — a calculated bearing BPFO/BPFI, gear-mesh frequency, the 1× imbalance (shaft) frequency or a fan blade-pass frequency. The tool reads each one’s level from the nearest 1/3-octave band in your Baseline and Current captures so you can watch it rise or fall. Watch frequencies persist in this browser.
How It Works
The comparator takes two short snapshots of your microphone’s spectrum — a Baseline (the machine in a known-good state) and a Current reading (today’s condition). For each capture it averages a high-resolution FFT over the whole window and sums the energy into 1/3-octave bands from 25 Hz to 16 kHz. It then overlays the two band spectra, draws a pink stripe over every band whose Current level rose by 6 dB or more, and ranks those risen bands largest-first — because a band that grows between captures is exactly where a developing fault tends to show up.
Why the before/after difference is trustworthy even without calibration
A browser microphone has an unknown sensitivity, and it is positioned some distance from the machine, so every absolute number it reports is in dBFS (decibels relative to digital full scale) carrying a fixed but unknown offset. The key insight is the same one behind any good before/after test: when Baseline and Current are captured with the same microphone, in the same position, at the same gain, that unknown offset is identical in both, so it cancels exactly when you subtract Current − Baseline. A band that reads +9 dB really did get about 9 dB louder. That is why the difference and the change in spectral shape are meaningful even though neither absolute level is calibrated.
Matching risen tones to mechanical faults
Rotating machines radiate sound at characteristic frequencies: the shaft turning frequency (1×, RPM ÷ 60) and its harmonics for imbalance and misalignment; bearing defect frequencies (BPFO, BPFI, BSF, FTF) from the bearing geometry; the gear-mesh frequency (teeth × shaft Hz) and its sidebands; and the fan/pump blade-pass frequency (blades × RPM ÷ 60). Calculate the ones that apply to your machine using the related tools below, add them as watch frequencies, and see whether their bands grew between captures. A rise at a calculated fault frequency is a useful early warning — but the order-to-fault and band-to-defect mappings are diagnostic conventions, not a guaranteed diagnosis, and you must verify your own inputs.
What stays uncalibrated
The single-capture numbers (“Baseline overall is −46 dBFS”) are not a vibration amplitude. They are not in mm/s velocity or g acceleration, and they cannot be used for ISO 10816 / ISO 2372 severity zones — that requires a calibrated accelerometer mounted on the machine and a proper analyzer. Consumer microphones also roll off at the frequency extremes and generally cannot pick up true low-frequency vibration that radiates little airborne sound, so a quiet low-speed shaft tone may simply not be audible. Treat this tool as a fast, free screening and trending aid that points you at frequencies worth a closer look with the right instrument.