Subwoofer setup guide

A good subwoofer setup depends more on the room than on the subwoofer. Where you put the sub and where you sit decide which bass frequencies get louder and which nearly vanish, because low frequencies form standing waves between the walls. Get placement right first, then set crossover, level and phase or delay, and use EQ last to tame the peaks that remain.

What does subwoofer placement actually change?

Below roughly 200 Hz the wavelengths are several metres long, comparable to the room itself. Sound reflects off the walls, floor and ceiling and combines with the direct sound, so the bass you hear at a seat is the sum of many arrivals. At some frequencies they add up and the bass booms; at others they cancel and the bass thins out. Moving the subwoofer changes how strongly it drives each of the room's resonances, called room modes, and changes the path lengths of its reflections.

That is why the same subwoofer can sound tight in one corner and boomy in another, and why two people on the same sofa can disagree about how much bass there is.

Corners, walls and the middle of the room

Every axial mode has a pressure maximum at the room boundaries, so a subwoofer in a corner couples to almost every mode at once. Corner placement gives the most output, but it also tends to give the most uneven response, because it excites the peaks just as effectively as the useful bass.

A subwoofer against the middle of the front wall sits halfway across the room's width, which is the pressure null of every odd-order width mode, so it drives those modes weakly. A subwoofer some distance out from a wall picks up a reflection-based cancellation instead: its reflection off the nearby wall arrives late enough to cancel the direct sound at roughly c / 4d, where d is the distance to that wall. A sub 1.4 m (4.7 ft) out from the wall has that null near 60 Hz; one 0.4 m (1.3 ft) from the wall pushes it above 200 Hz, out of the subwoofer's range. The 60 Hz null guide walks through that case.

Why the seat matters as much as the subwoofer

Moving the listener changes the response just as much as moving the source. A seat exactly halfway down the room sits on the null of the first length mode; a seat against the back wall sits on its pressure maximum. Many rooms have a deep dip in the middle and too much bass at the back wall.

If you can move the sofa, try seats away from the exact middle of the room and away from the rear wall. The standing waves guide explains where the pressure peaks and nulls sit for each mode.

Crossover, level, phase and delay

Once the subwoofer has a reasonable position, the bass management settings decide how it blends with the main speakers.

• Crossover. The frequency below which bass is sent to the subwoofer. 80 Hz is a common receiver default and a sensible starting point, but the right value depends on how deep your main speakers play cleanly and on how the sub and mains sum at the seats.
• Level. Match the subwoofer's level to the mains at the listening position, then adjust to taste. Judge level after placement, because placement changes how loud the sub sounds.
• Phase or delay. Around the crossover frequency both the sub and the mains are playing, and their arrivals need to add rather than cancel. Room correction systems usually set a distance or delay automatically; a phase control on the sub does a similar job. Check the result by measuring the combined response through the crossover region rather than trusting the number.

Do two subwoofers help?

Often, yes, and not mainly for more output. Two or four subwoofers in well-chosen positions can drive some room modes in opposite phase, so those modes cancel instead of building up, and the bass becomes more even from seat to seat. Welti and Devantier studied this in "Low-Frequency Optimization Using Multiple Subwoofers" (Journal of the Audio Engineering Society, 2006). In their rectangular-room analysis, configurations such as subwoofers at the midpoints of opposite walls, or at the midpoints of all four walls, reduced seat-to-seat variation compared with a single subwoofer.

Real rooms are rarely perfect rectangles, so treat those layouts as candidates to test rather than a recipe. Each added sub also needs its level and delay matched.

Measure the room, not one point

Because bass varies so much from spot to spot, a single measurement at one seat can mislead you: a position that looks great at the center seat may be poor two seats over. Compare candidate positions across the whole listening area. The guides below cover each step:

• How to find the best subwoofer position: a repeatable test loop.
• Subwoofer crawl explained: the quick listening method, and its limits.
• How to read a subwoofer frequency response: peaks, nulls and smoothing.
• Why bass disappears in some spots: what causes nulls and what moves them.

Seeing it with BassMap

BassMap for iPhone plays a continuous low-frequency test signal through your system while you walk the room. The phone tracks its own position, and the app draws a heatmap of each test tone's level across the area you walked, so you can see the dips and peaks between seats instead of guessing from one. Levels are relative, not calibrated SPL. Scan once, move the sub, scan again and compare the two maps side by side.