Speaker Frequency Sweep & Resonance Tester

Why the frequency slider is logarithmic

Human hearing perceives pitch logarithmically, not linearly. The difference between 20 Hz and 40 Hz sounds like the same musical interval as the difference between 10,000 Hz and 20,000 Hz, because both represent a doubling of frequency.¹ A linear slider would pack the entire bass range (20–500 Hz) into the leftmost 2% of travel, making precise subwoofer testing nearly impossible.

This tool maps a 0–1000 internal range logarithmically to 20–20,000 Hz, so the slider midpoint (500) lands at roughly 632 Hz rather than the 5000 Hz a linear scale would place there.¹ Bass and sub-bass frequencies occupy the lower third of slider travel, giving you the resolution you need where it matters most, and you can isolate a troublesome frequency by slowing your drag.

Choosing a waveform

The four waveforms differ in harmonic content, and picking the right one determines what the test reveals about your speaker or the room you are in. Sine is a pure fundamental with no harmonics, which makes it the cleanest signal available for isolating a single resonance frequency without other harmonics exciting adjacent resonances or masking the one you are trying to pin down.² Start here for most testing, and switch to a richer waveform only when the sine sweep leaves a question unanswered.

Square adds strong odd harmonics (3rd, 5th, 7th…), making it useful for crossover testing and stressing drivers with complex content.² Triangle has odd harmonics that fall off faster, so it serves as a middle ground for tweeter distortion checks that need less bite. Sawtooth contains all harmonics at full strength and is the harshest signal here, which suits amplifier headroom testing but grows fatiguing at high volume.³

Finding room resonances and rattle points

Room resonances (modes) are standing waves that build up at frequencies determined by room dimensions.⁴ They cause certain bass notes to sound disproportionately loud or muddy. To find them: run the Auto Sweep at slow speed (10 Hz/s) through the Subwoofer preset, and listen for frequencies where the sound seems to bloom or become uncomfortably loud despite no volume change.

Rattle points originate from loose panels, improperly fitted grilles, and furniture that vibrates in sympathy with the tone, so they are easier to locate using Manual mode. Sweep slowly through suspect ranges and pause the moment you hear a rattle, then check the frequency display for the exact Hz. Walk around the room while the tone plays, and the source will become obvious once you are close to it, letting you identify the offending panel or furniture piece quickly.

Subwoofer drop-off and roll-off testing

Two related tests share the Subwoofer preset, and both reveal whether your bass setup covers the range you expect. One finds how low your subwoofer holds output before roll-off swallows the bass; the other locates the crossover where your main speakers take over from the subwoofer. Running them back to back tells you whether a gap or a peak exists between the two.

Finding the subwoofer roll-off

Most home subwoofers have a low-frequency extension limit, typically somewhere between 20 and 30 Hz, below which the output drops sharply instead of holding steady.⁵ To find yours on this tool, set the Subwoofer preset, which spans 20 to 200 Hz, pick the sine waveform, and then sweep downward manually from 80 Hz. The point at which the subwoofer becomes noticeably quieter, or stops producing any audible output at all, is its roll-off frequency.

Locating the upper crossover point

Similarly, sweep upward from 80 Hz to locate the upper crossover point where your main speakers take over from the subwoofer. As you move through that transition region, listen carefully for any dip in output or any unexpected peak. A smooth, overlap-free handoff between the subwoofer and the main speakers produces a flat in-room response, while a gap or a pronounced peak at the crossover frequency points to a crossover setting mismatch that you can correct in your receiver or amplifier.

Understanding your driver's resonant frequency

Every driver has a resonant frequency (Fs), the point where it moves most freely with the least electrical energy input.⁶ Below that frequency, the driver's mechanical compliance acts as a spring resisting further excursion, and output drops steeply. Above Fs in a well-designed enclosure, output stays relatively flat until the high-frequency roll-off from moving mass takes over. Manufacturers specify Fs in the driver datasheet, and understanding it tells you the lowest useful frequency before bass response falls away sharply. Knowing this figure helps you decide where to set a subwoofer low-pass filter and whether a given driver can handle the bass content you plan to test.

How enclosures shift the resonant frequency

Finding your driver's practical resonance with the sweep takes under two minutes. Sweep slowly downward from 100 Hz with the sine waveform selected and listen for the frequency where the driver sounds most prominent just before output drops sharply. Sealed enclosures shift Fs upward compared to the free-air specification; ported enclosures are tuned below Fs to extend low-frequency output, which is why ported designs reach lower but roll off more steeply below the port tuning frequency.⁶ Building on this knowledge, you can set crossover and EQ filter points at frequencies that respect your driver's actual behaviour rather than guessing from marketing copy.