Subwoofer Test
Listen for the handover, then set the crossover and phase knobs on the sub or receiver. Match levels with pink noise, try the crawl and test LFE. This page plays tones. It does not turn those knobs.
These buttons do not move a knob. The phase tone and the level bands use 80 Hz. LFE bursts stay at 50Hz. After you listen, set the receiver crossover, or the sub's low-pass, to about 80 Hz if: The THX reference and the right default for most systems. Bass below 80 Hz is very hard to locate, so the sub stays invisible.
Start quiet. The volume starts at 15% unless this browser saved another level, and nothing plays until you click. Turn your amplifier down before you press play, then raise it slowly. Steady bass tones push a subwoofer much harder than music, and you hear them poorly, so it is easy to overdrive a driver without noticing. Stop if you hear chuffing, slapping or a buzz from the sub itself.
1. Crossover check: listen to the handover
A sine tone glides from 200 Hz down to 30 Hz at a constant level. This page does not filter it or move the crossover knob. Sit in your usual seat. If the receiver crossover is near 80 Hz, the mains fade and the sub takes over, and the tone should stay equally loud the whole way. Press a button when it clearly dips or swells. It reaches the sub only if the receiver sends bass there: set the speakers to Small, or plug the sub into a 2.1 output.
Localisation check
Each button plays pulsing bursts of narrow-band noise. Close your eyes and point to the sound. If you can point at the subwoofer instead of between your front speakers, mark that frequency.
Verdict: You could not point to the sub at any of these frequencies. Any crossover up to 120 Hz will stay invisible in your room.
2. Phase: make the sub and speakers push together
- Play the tone and sit in your main seat. This page does not turn the phase knob.
- Have someone flip the sub's phase switch between 0 and 180 degrees, or turn the phase knob slowly.
- Keep the setting where the tone sounds loudest at your seat. Louder means the sub and the speakers are adding up instead of cancelling.
- No helper? Change it, walk back, listen, and repeat. The difference is often several decibels, so it is easy to hear.
3. Level matching: sub band vs. mains band
Two bands of pink noise, each two octaves wide, split at 80Hz with 24 dB/octave filters. Because pink noise carries equal energy per octave, a well matched system makes both sound about equally loud. Adjust the sub level (or the receiver's subwoofer trim) until neither band jumps out. With a phone SPL app, set your receiver so each band reads around 75 dB (C-weighted) at the seat, but expect phone microphones to under-read the sub band, so trust your ears when they disagree.
4. Placement: the subwoofer crawl
- Put the subwoofer in your main listening seat, as close to where your head goes as you can.
- Start one of the bass loops below at a moderate level.
- Get down on the floor and crawl around the places the sub could actually go: the front wall, the corners and along the side walls. Keep your head about where the sub's driver would sit.
- Listen for the spot where every note is equally loud: no boom, no hollow or missing notes.
- Move the sub to that spot, go back to your seat and confirm. Then redo phase and level.
It works because sound travels the same way in both directions: what you hear at a spot with the sub in your seat is what you would hear in your seat with the sub at that spot.
5. LFE channel test
If your output has six or more channels, this sends pulsing 50Hz bursts to channel 4 (the LFE slot in standard 5.1 order) and nothing to the other speakers. Only the subwoofer should play. If the other speakers play it too, the output mixed the six channels back down. If nothing sounds, check that the receiver's subwoofer is switched on and that the LFE level is not muted.
Many receivers add about 10 dB to the LFE channel. This page does not add that gain, so the bursts can still be much louder than the other tests. Lower the volume first.
How subwoofer setup works
The crossover, explained
The crossover is the frequency where your receiver splits the signal: everything below goes to the sub, everything above to the speakers. Pick it about 10 Hz above where your speakers start to fade out, and usually no higher than 80 to 100 Hz. Do not stack two filters. If the receiver handles the crossover, set the sub's own low-pass knob to maximum or LFE, or you get a hole right at the handover.
Why phase and distance matter
At the crossover, the sub and the speakers play the same notes. If their sound arrives in step, it adds up; if one arrives half a cycle late, it cancels. An 80 Hz wave is 4.3 metres long, so a sub a couple of metres further away than the speakers can be badly out of step. The distance setting in your receiver and the phase control on the sub both fix this. Set the distance first, then fine-tune the phase.
Room modes and placement
Bass bounces between parallel walls and builds standing waves. At some seats certain notes boom, at others they nearly vanish, and the difference can be 15 dB or more. Placement changes which modes get excited, which is why the crawl beats any amount of EQ. Two subs on opposite walls smooth the response even more. For more on echoes and reverb, try the room acoustics test.
Common mistakes
The "sub too loud" mistake
Many people turn the sub up until they can hear it as a separate thing. A well set sub should disappear: you notice it most when you switch it off and everything sounds thin. If kick drums thud on their own and voices sound boomy, lower it 3 to 6 dB. Box claims of "room-shaking" bass mean little if the sub drowns out the music.
Typical good result
The sweep stays within a few decibels from 200 down to 35 Hz, you cannot point to the sub at 80 Hz, the phase setting gives a clear jump in loudness, and both noise bands sound equal.
Related tools
Find how low your system reaches with the bass test, check each channel of a 5.1 or 7.1 setup with the surround sound test, check left, right and the centre image with the stereo test, and measure echo and reverb with the room acoustics test.
Frequently asked questions
What should I listen for?
The sweep is a sine that falls from 200 Hz to 30 Hz over 30 seconds. It should stay about equally loud. Press Quieter here or Louder here when it dips or swells. Each localisation button plays 30 seconds of pulsing noise at 60, 80, 100 or 120 Hz. Close your eyes and see whether you can point at the sub. The level step plays pink noise in two bands around the frequency you picked, held on one band or swapping every 3 seconds for 60 seconds. The crawl loops a bass riff from 37 to 73 Hz, or noise from 25 to 120 Hz. Listen for notes that boom or drop out.
What does the phase tone do, and what do the degree buttons do?
The phase tone is a steady sine at the 60, 80, 100 or 120 Hz choice above, on both channels. It is not inverted. The 0, 90, 180 and 270 buttons do not flip it and do not turn the knob. Flip the phase switch or turn the phase knob on the sub, and keep the setting that sounds loudest at your seat. Use those buttons only to save a note of that knob.
Does this page set the crossover or the phase knob?
No. A browser cannot move those knobs. The 60, 80, 100 and 120 Hz buttons only choose the frequency the phase tone and the level bands use. The sweep is one full-range sine, not a filtered crossover. LFE bursts stay at 50 Hz. After you listen, set the receiver crossover, or the low-pass on the sub if the receiver is not splitting the bass. If the receiver handles the split, turn the sub low-pass to maximum or LFE so the two filters are not stacked.
How do I stop the sound?
Press Stop all, or press the same control again. The sweep button then says Cancel, the phase button says Stop tone, localisation says Stop plus the frequency, and the other tests say Stop. Each test starts only from a click. Nothing plays when the page opens. Leaving the page stops the oscillators and noise and closes the audio. The volume slider begins at 15 percent unless this browser saved another level. Master gain is that percent squared, so 15 percent stays quiet and 0 is silent.
Why might the sub stay silent, or other speakers play the LFE bursts?
The sweep, phase tone, level noise and crawl go to the normal stereo output. The sub plays them only when the receiver or a 2.1 output sends bass to it. Set the speakers to Small, or use a 2.1 jack. The LFE button plays 50 Hz pulses on channel 4 of 6 only when the browser reports at least six output channels. With fewer, it does not play. If the output refuses six channels, the bursts are mixed back down and other speakers can play them too. The page does not add the extra 10 dB many receivers apply to LFE, so lower the volume before that test.
What do the level bands and the trim slider do?
Pink noise is split at the frequency you picked. The sub band runs from one quarter of that frequency up to it, and the mains band runs from it to four times it. At 80 Hz that is 20 to 80 Hz and 80 to 320 Hz. Each edge uses two filters, a 24 dB per octave slope. Adjust the sub level, or the receiver trim, until the bands sound about equally loud. The trim slider only stores a note from -15 to +15 dB in steps of 0.5. It does not change how loud the page plays.
What is the subwoofer crawl on this page?
Put the sub in your listening seat, press Loop bass riff or Loop bass noise (25–120 Hz), and crawl the spots along the walls where the sub could go. The page only plays the loop. You move the sub. The even spot, with no boom and no missing notes, is where it should sit. Then sit down and check the phase tone and the level bands again.