Acoustics & Music Theory
why it sounds like that
Concept

Room mode — where it appears

A standing wave a room supports, with fixed places where the pressure is always maximum and places where it is always zero. Modes matter at low frequencies, where they are far enough apart to be heard as individual resonances rather than as a decay.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

Also named here as schroeder frequency — the same set of essays touches all of them, so they are one junction rather than several.

A small room's lowest modes. The first few axial standing waves of a room, drawn in plan, with the frequency of every mode below 160 hertz listed underneath. The low modes are far apart in frequency, so some bass notes are loud in one corner and absent in another. The sound buttons play these two octaves above their real pitch, because a room's lowest modes are below what most speakers reproduce.

The room is part of the instrument

A room has frequencies it supports and frequencies it will not. In a small one those frequencies are far apart, so some bass notes are loud in one corner and absent in another — and no equipment fixes it.

timbre · Room acoustics Where each room stops being a set of resonances. The Schroeder frequency of 6 rooms — a carpeted bedroom at 217 Hz, a domestic living room at 183 Hz, a rehearsal room at 120 Hz, a jazz club at 68 Hz, a shoebox concert hall at 21 Hz, a gothic cathedral at 36 Hz — marked on a logarithmic frequency axis with the ranges of 4 instruments underneath. Below the mark a room is a handful of separable modes and a note's loudness depends on where the listener is standing; above it the modes overlap and the room is described by one decay time.

Where a room stops being a room

A small room has frequencies it supports and frequencies it will not, and a hall has a reverberation time. Those are two separate accounts and they are descriptions of the same building at different frequencies. The crossover is one formula, and in a bedroom it lands at about two hundred hertz — in the middle of the bass register, and above nothing at all in a concert hall.

timbre · Room acoustics

Named alongside it

The objects these essays reach for when they reach for this one.

ReverberationSchroeder frequencyStanding waveAbsorptionDiffuse fieldResonanceSabine equation

All concepts