40 Hz test tone: check the bass in your room, seat by seat

Wikipedia's bass guitar article says a bass most commonly has four strings, tuned E1, A1, D2 and G2. E1 is 41.2 Hz, so 40 Hz sits 1.2 Hz below the lowest string.

One wave is 28 feet (8.6 meters) long in air, and one cycle takes 25 ms. The room adds its own pattern. The first length mode of a room is the speed of sound, about 1,125 feet (343 meters) per second, divided by twice the room's length. A 13-foot (4-meter) room has its first length mode near 43 Hz, which is above this tone. A room with another length puts its mode somewhere else, so what you hear depends on your own room.

Listen for four things: where the tone booms, where it thins out or disappears, whether one seat is much louder than another, and whether anything in the room buzzes. Give each spot a little time before you judge it. The subwoofer test tones page covers the full room walk, and the room resonance page explains where the peaks come from.

If the tone vanishes from a small desktop sub while 80 or 100 Hz plays fine, the sub may be one of these. Wikipedia's Subwoofer article says many multimedia subwoofers might better be called mid-bass cabinets covering 80 to 200 Hz, since they're too small to produce deep bass in the typical 20 to 100 Hz range.

On a phone or laptop, a 40 Hz tone may barely come through. Those speakers are much smaller than a subwoofer driver, so play the tone through a subwoofer before you judge the result.

Two things change what 40 Hz sounds like: where the sub stands and where you sit. Move one at a time, so you know which one made the difference.