Subwoofer placement and the subwoofer crawl

Why placement matters so much for bass

At low frequencies, sound waves are as long as your room: about 11 feet at 100 Hz and 23 feet at 50 Hz. They bounce between the walls and pile up into room modes, standing patterns where some spots get far too much bass and others almost none. Move your head two feet and a bass note can go from booming to thin.

Two positions decide what you hear: where the subwoofer is, and where you sit. Changing either changes which modes get excited and which you sit in. That’s why the same subwoofer can sound tight in one corner and boomy in another, and why no rule can tell you the best spot for every room.

Step 1: pick a starting point

Manufacturers mostly agree on where to start, and disagree a little on why:

Corners give the most output because each boundary reinforces the bass. Genelec’s idealized figures are up to +6 dB with one wall, +12 dB where a wall meets the floor, and +18 dB in a corner, compared with a speaker in free space. In a real, furnished room the boost is smaller and uneven, which is the catch: a corner also excites every room mode at once, so some notes boom.

A front position also helps the sub blend with the main speakers, so bass seems to come from the screen rather than from behind you.

Step 2: the subwoofer crawl

The subwoofer crawl uses a simple fact of physics: sound travels the same way in both directions between two points. So instead of moving a heavy sub around and running back to the sofa each time, you swap places.

1. Put the sub on your main seat, or on the floor right in front of it.
2. Play steady, repetitive bass: a bass-heavy music track or a film scene you know well. A test tone sweep works too, but music is easier to judge.
3. Get down on the floor and crawl slowly around the area where the sub could go: along the front wall, into the corners, beside the TV console. Keep your head near the height of the sub’s driver.
4. Listen for evenness, not loudness. You want the spot where the bass notes sound equally strong, without one booming and another vanishing.
5. Mark the best spot, put the sub there, and listen from the seat to confirm.

Step 3: check the seat too

The crawl finds the best place for the sub; the seat matters just as much. In our 1,000-room simulation, moving the seat along the room changed how even the bass was by about as much as moving the sub. A few positions are worth knowing about:

• Right against the back wall. Bass builds up at walls: in our simulation, a head against the back wall got about 4 dB more bass than the room average. It’s even, but heavy, which is what people hear as boom. CEDIA/CTA RP22 recommends keeping listeners off the back wall where possible.
• The exact middle of the room. The first length mode has a dead spot halfway between the front and back walls, so the lowest notes can thin out there.
• About 62% of the way back (38% from the back wall). With the sub at the front, this was one of the least even positions in our simulation, even though the popular “38% rule” says it should be as good as 38% from the front.

The “38% rule” itself (sit about 38% of the room’s length from the front wall) did better than average in our simulation, but it’s a starting point for listening, not a guarantee.

Step 4: dial in the settings

Once it’s placed, a few settings make a real difference:

• Run your receiver’s room calibration. SVS recommends setting the sub’s phase to 0 and its low-pass filter to its highest setting (or off) first, so the receiver can manage the crossover.
• Phase. If your sub has a 0/180° switch, Klipsch’s advice is to pick whichever gives more bass at your seat. Sonos sets it automatically with Trueplay.
• Level. Set it so bass sounds balanced with the speakers, not as loud as possible. Room calibration usually gets close.

When two subwoofers are better than one

If several people watch, one sub can only optimize one seat. Harman’s Todd Welti and Allan Devantier studied this in detail: well-placed multiple subs cut the difference in bass from seat to seat dramatically, and two subs at the midpoints of opposite walls were nearly as effective as four. Four did best overall, at the cost of more boxes in the room. In their measured rooms, optimized multi-sub setups also gained 3 to 6 dB of maximum output.

CEDIA/CTA RP22 sets targets for how much bass may vary from the main seat to the others: within ±4 dB at its Level 2, tighter at higher levels. A single sub rarely meets those in a multi-row room; two usually can.

Subwoofers in apartments

Bass travels through floors and walls far more readily than higher sounds. KEF’s advice for apartments:

• Avoid corners: the extra output carries next door.
• Keep the sub away from shared walls, ideally against an outside wall or near a structural column.
• Move it closer to your seat: it needs less total output to sound full where you are.
• Isolation feet help a little: KEF says they reduce transmission by a decibel or less. Some subs, like KEF’s KC62, have an apartment mode that cuts the deepest bass.