Subwoofer test tones

Four jobs, four sets of frequencies, done in this order so each step does not undo the last.

Before you start

Use sine waves only. A square wave at 30 Hz contains energy at 90 Hz and above, so a subwoofer that produces nothing at 30 Hz will still make a sound and you will conclude it goes deeper than it does. Everything below assumes a sine from the tone generator.

Keep the level moderate and never leave a low tone running unattended. A subwoofer has to move its cone furthest at the bottom of its range, and a sustained loud tone below its limit is one of the few genuine ways to damage a driver. If you hear knocking or slapping rather than a tone, stop immediately: that is the coil hitting its end stop.

1. Find where it actually stops

Play 50 Hz, then step down: 40, 35, 30, 25, 20. Listen and feel for where the output falls away sharply. Most domestic subwoofers produce usefully down to 25 to 30 Hz, and the very bottom is usually felt through the floor rather than heard as a pitch.

The bass test does the same job as a sweep if you would rather not step by hand. Note the number — everything else depends on it.

2. Choose a crossover

The crossover is where the main speakers hand over. Find where your main speakers stop by running the bass test through them with the subwoofer off, then set the crossover slightly above that point rather than exactly at it. Speakers that fall away from 90 Hz want a crossover around 100 to 110 Hz, not 80, or you leave an audible hole in between.

The common default of 80 Hz suits speakers that genuinely reach 60 Hz. It is a poor default for small desk speakers, which is why so many systems with a subwoofer still sound thin in the upper bass.

3. Set phase and position

Play a tone at the crossover frequency through the whole system and sit in your normal listening position. Switch the subwoofer's phase control between its settings and pick whichever is louder and more solid. If the difference is obvious, phase was wrong; if it is subtle, either is fine.

Placement matters more than any setting. A useful technique: put the subwoofer temporarily in your listening seat, play a tone around 40 to 60 Hz, and crawl the perimeter of the room. Where it sounds loudest and most even is where the subwoofer should go, because the physics works the same in both directions.

4. Match the level

Play a tone just above the crossover, note how loud it is, then play one just below and match the subwoofer's gain so the two feel equally loud. This is duller than setting it by ear with music and produces a far better result, because music constantly changes and an unchanging tone does not.

Resist the temptation to set it high. A subwoofer that you can locate by ear is set too loud — done properly, the low end should seem to come from the main speakers, with the subwoofer only announcing itself when you turn it off.

Room nulls, and why one seat has no bass

A 40 Hz wave is about eight and a half metres long, so in any normal room it reflects and interferes with itself, producing positions where a frequency reinforces and positions where it nearly cancels. A seat sitting in a null at 45 Hz has no bass at 45 Hz, and no amount of gain fixes it — raising the level raises the cancellation too.

Find them by playing a steady tone and walking the room, or by sliding the tone slowly while seated. If you find a deep dip, move the subwoofer or the seat. Equalisation can tame a peak fairly well and can almost never fill a null.

Rattles come last

Once the subwoofer is set, sweep slowly from 30 Hz to 120 Hz and listen for buzzing that is not the tone. Doors, vents, picture frames, light fittings and loose cabinet panels all resonate somewhere in that region. Find the frequency, hold it, and press on things until it stops — that is the object to fix, and it is almost never the subwoofer itself.

Last reviewed 2026-09-22.