Why bass can fade at different rates in connected rooms

A connected home is not one simple room

Room-acoustic explanations often begin with a single enclosed space. Real homes contain open-plan areas, corridors, stairwells and doors that may be open, closed or partly open. These spaces exchange sound, but they do not necessarily behave as one uniform volume.

At low frequencies, wavelengths are comparable with room dimensions. The sound field is then strongly influenced by room modes: spatial patterns with peaks and dips that depend on geometry, frequency and the positions of the source and receiver.

What the 2026 study modelled

A peer-reviewed study in Archives of Acoustics used numerical simulations to examine two connected rectangular subrooms. The larger room was highly reverberant, while the smaller room had more sound absorption on its boundaries. The researchers excited the system with a harmonic source and examined how low-frequency sound decayed after the source stopped.

This was a controlled computer model, not a survey of occupied homes. Its value is therefore in explaining a mechanism rather than supplying a ready-made prediction for a particular living room.

The decay was not one straight line

In a simple textbook picture, sound energy falls at a broadly exponential rate after a source is switched off. In the modelled connected rooms, the low-frequency decay was usually non-exponential. Different modes carried energy for different lengths of time, so a single decay rate could conceal the shape of the response.

Some modes were localised mainly in one subroom. Modes concentrated in the more reverberant space decayed slowly, while other modes interacting more strongly with the better-damped space lost energy faster.

Moving the source changed the result

The simulations also found that decay in the larger room depended on where the source was placed. When the source was in that reverberant room, slowly decaying localised modes dominated. When it was in the smaller, more absorbent room, the larger room's response decayed faster because different modes were excited.

This helps explain why a low hum, loudspeaker or piece of equipment can appear more persistent from one position than another. It does not mean that moving any source will deliver a fixed improvement; the outcome depends on the frequency, geometry, opening and surfaces.

One reverberation figure may be incomplete

ISO 3382-2 sets out methods for measuring reverberation time in ordinary rooms. Such measurements are useful for comparing rooms and for corrections in other acoustic tests. But a connected low-frequency system can require closer examination of the decay curve, individual frequency bands and multiple positions rather than reliance on one broadband figure.

The practical question is not simply how reverberant the home is. It is whether a particular frequency is being stored in a particular part of the layout and whether the measurement represents the location where the sound is actually noticed.

What I would check in a real home

A real investigation should begin with the source and the way rooms are connected. Soft furnishings may help at mid and high frequencies but are not automatically effective against a low-frequency modal problem.

• Identify whether the sound is steady, intermittent or only noticeable after an event stops.
• Compare positions rather than relying on a measurement at one point.
• Record the state of doors and other openings during the assessment.
• Examine narrow frequency bands where a hum, boom or long decay is strongest.
• Distinguish sound travelling through an opening from structure-borne transmission through the building.
• Test a proposed treatment against the dominant frequency and path before applying it widely.