Room Dimension Calculator — Modal Distribution Check

Several published ratio sets aim to spread room modes evenly (height : width : length, normalised to height = 1). Verified small-room ratios from Everest & Pohlmann, Master Handbook of Acoustics: Sepmeyer 1:1.14:1.39 and 1:1.28:1.54; Louden 1:1.4:1.9; Boner 1:1.26:1.59; IEC 268-13 1:1.25:1.6. Larger published ratios — Sepmeyer 1:1.6:2.33 and Volkmann 1:1.5:2.5 — suit bigger rooms but fall outside this calculator’s compact-room window, so it scores them lower. Avoid integer ratios (1:1, 1:2, 2:3), which cause coincident modes.

It normalises your dimensions to the smallest (length÷height and width÷height), then measures the distance from the Bolt-area centroid near IEC 268-13 / Boner (length÷height ≈ 1.6, width÷height ≈ 1.3). Inside the acceptable window (length÷height 1.1–2.1, width÷height 1.1–1.9) it grades Excellent / Good / Acceptable by that distance; outside the window it returns Poor. These bands are a guide, not a substitute for the EBU Tech 3276 / Walker inequality (1.1·w/h ≤ l/h ≤ 4.5·w/h−4) used for broadcast listening rooms.

Room modes are resonant frequencies determined by room dimensions. Axial modes (between two parallel surfaces) are the strongest. The first axial mode frequency for each dimension is f = n × speed of sound ÷ (2 × dimension), with n = 1 for the fundamental. Modes cause peaks and nulls in bass response at specific positions.

Acoustic treatment (bass traps, diffusers) can significantly reduce the severity of modal problems but cannot eliminate them entirely. Starting with good proportions and adding treatment is far better than trying to treat a poorly proportioned room. Treatment is essential regardless of ratios.

Larger rooms have lower first mode frequencies and more evenly distributed modes. A minimum of 30–40 cubic metres is recommended (EBU Tech 3276 specifies a minimum floor area of 40 m² for reference listening rooms — 30 m² for sound control rooms — and a maximum volume of 300 m³). Below 20 cubic metres, low-frequency problems become severe. If your room is small, focus on nearfield monitoring and heavy bass trapping.