Subwoofer placement and integration: crossover, phase and dual subs
Where the sub sits decides more than which sub you bought. Placement, crossover, phase and a second sub, in the order that fixes boomy bass.
Where should you put a subwoofer?
Wherever it sounds smoothest at the seat you actually sit in, and that is rarely where it looks best. Below about 200 Hz the room stops behaving like open space: its dimensions set up standing waves (room modes) that pile bass up in some spots and cancel it in others, so the same sub can sound bloated at the sofa and thin a metre to the left. Moving the sub changes which modes it excites; moving the seat changes which peaks and dips you hear. A corner excites the most modes, which is why a corner sub sounds loudest and why it is so often the boomiest place in the room. Treat placement as the first and cheapest piece of equalization you will ever do, before any receiver setting. The fastest way to find the spot is the subwoofer crawl, which our speaker placement guide walks through step by step: put the sub in your listening seat, play a bass-heavy passage, crawl along the walls where the sub could live, and wherever the bass sounds most even is where the sub goes.
What crossover should you set for a subwoofer?
Start at 80 Hz, the THX convention most receivers default to, then move it only for a reason. In the receiver, set your speakers to "Small" so everything below the crossover is sent to the sub rather than asked of the speakers, which is what lets small bookshelf speakers work in a home theater at all. Raise the crossover for speakers that run out of bass early, such as small satellites or on-wall models, and lower it for full-range towers only if they genuinely play cleanly below it in your room. One trap catches almost everyone: the sub's own low-pass knob. When the receiver is doing the crossover, set the sub's knob to its highest setting or its LFE/bypass position, otherwise two filters stack and leave a hole just above the crossover point. And when you compare a speaker's quoted low-frequency limit against a crossover setting, read the tolerance next to it first: a figure at −6 dB and a figure at ±3 dB are not the same promise, which the apartment subwoofer guide shows with real catalog rows.
What is the LFE channel, and is it the same as the subwoofer output?
No. LFE is the ".1" in 5.1: a separate low-frequency effects channel in a Dolby or DTS soundtrack, mixed for playback 10 dB louder than the other channels so effects have headroom. The receiver's subwoofer output carries that LFE channel plus all the bass it redirects from speakers set to "Small". So a sub plays bass even in a stereo track with no LFE at all, and turning the LFE level down does not tame the bass from music. Two settings live here. The receiver's LFE low-pass filter caps how high the LFE channel itself reaches (120 Hz is the usual default and a safe one). The subwoofer level is a separate trim, best set by the receiver's calibration and then checked by ear, because a sub set a few dB hot is the most common reason a system sounds boomy.
How do you set subwoofer phase and distance?
Let the receiver set distance, then use phase to fix what is left at the crossover. Distance (delay) tells the receiver how far each speaker is from you so their sound arrives together; room correction measures and fills it in automatically, and it is worth leaving alone unless you are tuning with a microphone. Phase matters where the sub and the main speakers overlap, around the crossover frequency, because two sources playing the same note out of step cancel each other. Sitting in the main seat, play a test tone at the crossover frequency, or a bass line you know well, and flip the sub's phase switch between 0° and 180° (or turn a continuous phase dial slowly). Keep the setting that sounds loudest and fullest at that frequency. Then re-run the receiver's room correction, because changing phase changes the response it measured. Our room correction guide covers what those systems adjust and what they cannot.
Are two subwoofers better than one?
Usually, but for evenness more than loudness. A single sub's bass varies a lot from seat to seat because each seat sits on a different part of the room's modes. Two subs in different places excite those modes differently, so peaks and dips partly cancel and every seat hears something closer to the same bass. Harman's published research (Todd Welti's multiple-subwoofer studies for the Audio Engineering Society) found that two subs at opposite wall midpoints, or four at the wall midpoints or the corners, reduced seat-to-seat variation far more than any single position did. The practical rules: two identical subs are simplest to integrate; the receiver needs two subwoofer outputs or the signal has to be split; and each sub then runs at a lower level, which is cleaner. The builder reads your receiver's stated subwoofer outputs: it tells you when a receiver with one sub has a second output free, and warns when your subs outnumber the outputs. And the sealed versus ported guide covers what kind of box to double up on.
Do you need REW and a measurement microphone?
Not to get good bass, but it is the only way to know you have it. Room EQ Wizard (REW) is free measurement software: plug a calibrated USB microphone into a laptop, put the mic at your seat and it plots the frequency response you are actually hearing. That turns the crawl, the crossover and the phase decisions from guesswork into before-and-after graphs. Two readings matter most: big peaks, which equalization can pull down, and deep narrow dips, which it cannot fill, because a dip is cancellation and boosting it only feeds both waves that are cancelling. Dips are fixed by moving the sub, moving the seat, or adding a second sub. A receiver's own room correction already does a version of this measurement for you; REW is how you check its work.
Which subwoofer should you integrate?
Choose the box for the room, then integrate it with everything above. In a small room or an apartment, a sealed sub usually integrates more easily, because its gentle roll-off sits on top of the bass boost a small room gives you anyway; our apartment subwoofer guide has the picks and the spec fine print. In a large room, ported boxes earn their output, and the sealed versus ported guide works through the trade. Browse subwoofers by enclosure and driver size, then put your choice next to your receiver in the builder, which checks the subwoofer outputs and says "can't check" where a sheet leaves a field blank, rather than passing the pairing.