How to Test a Subwoofer and Find Your Speakers' Real Bass Limit

Every speaker specification sheet claims a frequency range, and a lot of them are close to fiction. “20 Hz–20 kHz” printed on a small bookshelf speaker means very little, because it omits the only part that matters: how far the output has dropped off by the time it gets there.

Test tones settle the argument. They cost nothing, they take ten minutes, and they tell you what your gear actually does rather than what the box says.

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What “bass” actually is

Splitting the low end into bands makes the test far more useful than treating it as one lump:

Sub-bass, 20–60 Hz. Felt more than heard. Cinema rumble, the lowest organ pipes, the bottom of an 808. Requires a real subwoofer or a large driver.
Bass, 60–120 Hz. Kick drums, bass guitar fundamentals, the weight in most music. This is the band most people mean.
Upper bass, 120–250 Hz. Warmth and body. Male vocals live at the top of this range.

Most small speakers roll off somewhere in the 60–100 Hz region. Phone speakers manage almost nothing below about 400 Hz, which is why they sound thin no matter what you do to the EQ.

The descending tone test

This is the core of it, and it takes two minutes.

Set a comfortable, moderate volume with a mid-range tone — around 1 kHz — as your reference. Do not change the volume again during the test. Changing it invalidates everything.
Play a 200 Hz tone. You should hear it clearly.
Step down: 150, 120, 100, 80, 60, 50, 40, 30, 20 Hz. Give each a few seconds.
Note where it gets noticeably quieter, and where it effectively disappears.

The first number is your real usable limit. The second is where the speaker stops entirely. On a decent bookshelf pair, expect the drop somewhere around 55–70 Hz. On a good subwoofer, you should still feel 30 Hz in your chest and in the furniture.

The trap: distortion sounding like bass

Here’s what makes this test genuinely worth doing rather than just interesting.

When you feed a speaker a frequency below what it can physically produce, it doesn’t go silent. It produces harmonic distortion — multiples of the tone you asked for. Ask for 30 Hz from a driver that can’t do it, and you may hear a weak 60 Hz and 90 Hz instead.

So you hear something, and conclude the speaker reaches 30 Hz. It doesn’t. You’re hearing it fail.

How to tell them apart: a pure test tone should sound smooth and featureless, like a hum with no texture. If the “bass” sounds buzzy, gritty, raspy, or has an audible pitch higher than you expect, that’s distortion. Compare directly with a 100 Hz tone, which almost anything can play cleanly — the difference in character is obvious once you’ve heard it side by side.

Checking a car system

Cars are the most rewarding place to run this test, because cabin gain genuinely boosts low frequencies and the results are often better than at home.

Engine off, doors closed. Road and engine noise sit right on top of the bass band.
Turn off every processing option you can find — loudness, bass boost, and any “surround” mode. These lie to you by design.
Run the same descending sweep and watch for panel rattle. A rattling door card at 45 Hz is not your subwoofer failing; it’s a trim clip. Fix that before you blame the audio.
Move your head around. Bass in a small enclosed space forms standing waves, so one seat may have a null where another has a peak.

Setting a subwoofer crossover properly

If you have a separate sub, this test is how you set it up instead of guessing:

Find where your main speakers drop off, using the method above with the sub switched off.
Set the crossover about 10–20 Hz above that point, so the sub takes over before the mains run out rather than leaving a gap.
Play a tone right at the crossover point and walk around. If the bass seems to vanish and reappear as you move, you have a phase problem — flip the sub’s phase switch and try again.
Match levels by ear at a tone just above and just below the crossover; they should sound equally loud.

Please protect your equipment

Two real warnings, neither of them theoretical:

Sustained low tones at high volume damage drivers. A subwoofer asked to play 25 Hz at high level for a minute is doing far more work than any music demands. Keep test tones brief, and stop immediately if you hear a mechanical knocking sound — that’s the voice coil hitting its limit.

Never run a sweep through headphones at high volume. Headphones can reproduce deep bass at levels that are genuinely dangerous and don’t feel loud while they’re happening.

Frequency Generator has both the single-tone and sweep tools this needs, with decimal precision so you can step carefully through the region where your speakers give up. Use it once on each set of speakers you own — the results tend to change how you think about your EQ settings.