Subwoofer crawl explained

The subwoofer crawl is a quick way to find a good subwoofer spot by ear: put the subwoofer at your listening seat, play bass, then crawl around the room where the sub could go and listen for the place where the bass sounds most even. It works because swapping the source and the listener gives, in principle, the same bass response. It is a useful shortlist tool, but it optimizes one seat and relies on your ears, so verify the result.

Why does the subwoofer crawl work?

At bass frequencies a room behaves, to a good approximation, like a linear system. In a linear system, acoustic reciprocity applies: the transfer function from a source at point A to a listener at point B is the same as from a source at B to a listener at A. So if the subwoofer sits at your seat and your ear is at a candidate floor position, you hear roughly what you would hear at your seat with the subwoofer at that floor position.

That lets you audition many positions in a few minutes without dragging a heavy sub around the room between every test.

How to do a subwoofer crawl

1. Put the subwoofer at the main listening seat, as close to ear height as is safe and practical.
2. Play repeating bass content with steady level across the low range: a bass-heavy music track you know, or low-frequency pink noise. Single test tones can mislead, because they reveal one frequency at a time.
3. Set a moderate volume and keep it fixed.
4. Get down to where the subwoofer's driver would be, near the floor, and move along the walls and other places the sub could live.
5. Listen for the spot where the bass sounds most even: individual notes at similar loudness, no boom, no notes that disappear.
6. Mark the two or three best spots with tape.
7. Move the subwoofer to each marked spot and listen from the seat to choose between them.

Where the subwoofer crawl misleads

The method is clever, but the conditions it assumes are only partly true in a real living room.

• It optimizes one seat. Reciprocity only swaps one source with one listening point. A position that sounds great at the main seat can be poor for the rest of the sofa, and the crawl gives you no information about the other seats.
• The geometry is rarely exact. For a true swap, the sub would sit with its driver where your ears normally are, and your ears would be where the driver will be. In practice the sub sits on a seat cushion and you listen with your head near the floor, so both points are approximate.
• The room changes when the sub moves. A subwoofer in the seat, and your body on the floor, sit where they will not be later. Furniture and the sub's own cabinet near a wall also affect the result once it is moved back.
• Ears are poor at judging nulls. Hearing adapts quickly, loudness perception at low frequencies is uneven, and a narrow dip is easy to miss in music. Ears notice peaks more reliably than dips.
• Floor-level listening is not seat-level listening. Close to the floor you are near a boundary, where pressure builds up, so everything can sound bassier than it will at the seat.

Subwoofer crawl vs measuring at the seats

A measurement replaces your ears with a microphone, so the result is repeatable and shows narrow nulls that the crawl misses. Measuring each candidate position at each seat takes longer, but it answers the question the crawl cannot: how the bass varies across the whole listening area.

A practical combination is to crawl first to find two or three promising positions, then measure those positions properly at every seat, following the test loop in how to find the best subwoofer position. Reading the resulting curves is covered in how to read a subwoofer frequency response.

What the crawl cannot fix

Some rooms have a mode that causes a deep null right at the main seat whatever the subwoofer position, for example a seat exactly halfway down the room on the first length mode. No subwoofer position fixes that for a single sub, because the problem belongs to the seat. Moving the seat, adding a second subwoofer, or both, are the options. See standing waves in room acoustics for where those seat-bound nulls come from.

Checking a crawl result with BassMap

BassMap for iPhone measures the other direction. With the subwoofer in its candidate position, you walk the listening area while the app plays a low-frequency test signal through your system, and it maps each test tone's level across the area you covered. That shows whether the spot you found by crawling also works for the seats beside the main one. Levels are relative, not calibrated SPL.