Why bass gets boomy, and where it hides.
Every room has a few low notes it loves too much. Scroll down and step inside a room to watch bass pile up in some places and vanish in others. Then drag the listener around and hear, in your mind’s ear, why one seat sounds so different from the next.
One note, one pair of walls
The lowest note that fits between the two end walls. Air piles up at the walls (warm) and hardly moves in the middle (cool). That is an axial mode.
Text alternative: a standing-wave illustration of a rectangular room. Warm colours mark places where the air pressure swings most, so that note sounds loud there. Cool colours mark nodes, where it is nearly silent. The picture steps through axial, tangential and oblique modes as you scroll, and you can drag the listener or use the seat sliders.
The first low notes of a 4.2 × 3.1 × 2.5 m room
This is an example room, not yours. The level bar shows how strongly each note is heard at the seat in the picture. Drag the listener, use the seat sliders or change the example room, and watch the bars change.
| Note | Kind | Heard at the seat |
|---|---|---|
| 40.8 Hz | Axial (1·0·0) | 43% |
| 55.3 Hz | Axial (0·1·0) | 25% |
| 68.6 Hz | Axial (0·0·1) | 6% |
| 68.8 Hz | Tangential (1·1·0) | 11% |
| 79.8 Hz | Tangential (1·0·1) | 3% |
| 81.7 Hz | Axial (2·0·0) | 62% |
| 88.1 Hz | Tangential (0·1·1) | 2% |
| 97.1 Hz | Oblique (1·1·1) | 1% |
| 98.6 Hz | Tangential (2·1·0) | 16% |
| 106.7 Hz | Tangential (2·0·1) | 4% |
Three kinds of mode, one boomy room.
You have just seen all three. A simple rectangular room has a great many of them in the low notes. When two sit close together they sound like one fat, boomy note. When there are big gaps between them, some notes feel thin and missing.
Axial
Between one pair of walls. The strongest and easiest to hear, and usually the ones behind a boomy note.
Tangential
Around four walls at once. Gentler, but there are many more of them.
Oblique
Using all six surfaces. Each is mild, and together they fill in the background.
A bass note is as long as your room.
At 50 Hz a single wave measures nearly seven metres from crest to crest. That is the same size as many studios and living rooms, so the room itself starts to play along. Where you put the speakers and where you sit decides how much of it you hear.
Treating bass starts with knowing which notes, and which spots, are the problem.
Your own room, in the same 3D view.
See where bass piles up
A map of loud and quiet spots across your floor, for the note and the speaker position you choose.
Your room's trouble notes, listed
The low notes your room's shape is likely to exaggerate, in order, each labelled by type.
Crowded notes and empty gaps flagged
Notes bunched together that sound like one boom, and wide stretches with nothing to support the bass.
Try seats before you move anything
Drag the listener around the room and get a short list of seats worth trying first.
Room modes, and the rest of the kit, for £149 a month.
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How it works, and its limits
The pictures and lists use the standard modal formulae for a simple rectangular room with rigid, perfectly reflective walls. Real rooms have absorption, furniture, doors, windows and awkward shapes, which broaden and shift every mode, so the frequencies and levels here are an indicative design guide, not a measurement of your room.
Wave pictures are an illustration of the idea. They show where air pressure swings most and least for one note at a time, not a prediction of what you will hear. The room in the worked example (4.2 × 3.1 × 2.5 m) is an example only.