🎵 Room Acoustics

The Schroeder frequency, estimated here as f = 2000√(RT60/V), marks the transition between distinct modal behaviour and a diffuse statistical sound field. Below it individual room modes dominate and equalisation cannot fix the problem; only physical acoustic treatment can. Above it the modes overlap so densely that the room behaves more like a reverberant space.

The simulator uses the Sabine formula, RT60 = 0.161V/(αS), where V is the room volume, S is the total surface area and α is the average absorption coefficient. It assumes a 2.5 m ceiling height to compute volume and surface area from your chosen width and depth. Higher absorption shortens the reverberation time.

Axial modes bounce between just two parallel surfaces and are the strongest, so they cause the most audible colouration. Tangential modes involve four surfaces at once and are typically about 3 dB quieter, but they still tint the sound. The simulator lets you select axial X, axial Y, and several tangential modes to compare their patterns.

The pressure field varies across the room, so placing a speaker or your ears at an antinode receives maximum energy at that frequency, exaggerating the resonance. Sitting at a node almost cancels it. The listener SPL readout shows the relative level at the chosen mode, which is why moving a sofa can transform how a room sounds.

It captures the correct modal frequency relationships and standing-wave geometry for an idealised rectangular room. It is a 2D plan, so the vertical height mode series is not drawn, and it assumes rigid walls and a single mode at a time rather than the full superposition of all modes. RT60 and Schroeder values are standard engineering estimates, not measurements.

Low frequencies have wavelengths comparable to room dimensions, so they form strong standing waves where they pile up energy. Rooms with low absorption let these modes ring for a long time, producing booming peaks and hollow dips between roughly 50 and 300 Hz. This is why bass is the hardest part of the spectrum to control in small rooms.

Bass traps, such as thick mineral-wool panels and corner stacks, raise absorption at low frequencies, reducing the Q of modes and lowering the Schroeder frequency. Asymmetric room proportions, for example 4.7 : 3.6 : 2.9 m, spread modes more evenly so they do not coincide. Together they give a flatter, more neutral response that is far easier to mix in.