A subwoofer that booms or vanishes is a placement, crossover and level problem. Three settings decide whether it blends with the speakers or fights them.
Set the crossover near **80 Hz** or twice the speaker's -3 dB point, place the sub on the **same wall** as the speakers, and match level with **pink noise** before you touch any EQ.
A corner adds roughly 6 dB of low end and a boom you cannot EQ away later. Start on the same wall as the speakers, slightly off-centre, and keep at least 20 cm to the wall behind the port.
With small speakers the sub takes everything below the crossover and the speakers are freed from deep bass. With floorstanders you can run them full range and low-pass the sub only, but then both play the same octave.
Pick 80 Hz or twice the speaker's -3 dB figure. On an AV receiver set the speakers to **Small** and the crossover there, then disable the sub's own low-pass or set it to bypass.
Receiver: speakers Small, crossover 80 Hz
Sub: LPF bypass or maximumPlay pink noise on each channel in turn and measure at the listening position with a phone meter. Raise the sub until it sits 3 to 6 dB above the mains, then confirm with a bass sweep that no frequency drops out.
Switch the phase between 0 and 180 degrees and keep the position where a sine sweep around the crossover sounds fullest. A sub that cancels the mains sounds quieter than it measures.
Use one track with a known bass line and one film scene with a sustained rumble. If the sub only appears on explosions, the level is too high and the crossover too high.
Corner placement plus high gain. Move the sub away from two walls and lower the level before changing the crossover.
Crossover is applied twice, or the receiver sends nothing below 80 Hz. Set the speakers to Small and bypass the sub's filter.
Ground loop between sub and receiver. Use the same outlet, or insert a ground loop isolator on the audio cable.
A room mode. Move the sub along the wall or add a second sub; EQ can only fix one seat at a time.
It matches the low limit of most bookshelf speakers and keeps voices out of the sub. Larger speakers can cross lower.
For a single seat yes. Two smaller subs even out room modes better than one large sub.
Set the receiver back to Large speakers with the sub on LFE and return the sub's gain to its previous position. No file or setting outside the audio chain changes.
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