Learn Hiring and planning

Three problems, three fixes

Why how a room sounds, how its sound system plays and how much sound escapes are three different problems, each with its own fixes.

Three questions, three sets of tools

  1. Room acoustics

    Does it sound clear, warm and controlled inside?

    How the room itself treats sound: how long it rings on, which bass notes it exaggerates, and how its reflections colour what you hear.

    Fixed with
    Absorption, starting with the ceiling in a small room; diffusion; bass traps where the bass needs them.
    Measured as
    RT60 per octave band, and the bass response at the seats.

  2. The sound system

    Does everyone hear even, clean sound at the right level?

    The speakers, where they stand and point, and the processing that feeds them.

    Fixed with
    The choice of speakers, where they go and how they are aimed, a plan for the subwoofers, and DSP for EQ, crossovers, delay and limiting.
    Measured as
    Coverage, SPL, headroom and frequency range.

  3. Isolation

    Does sound stay in, and outside noise stay out?

    What the building lets through, in both directions.

    Fixed with
    Mass, airtightness and decoupling: doors and seals, glazing, isolated ceilings or walls, silencers in the ducts, and a limiter policy.
    Measured as
    Sound insulation values, and the levels measured at the neighbours.

Absorption is not isolation

This is the mix-up that costs the most. Acoustic panels, foam and soft furnishings are light and porous by design: they let sound in and turn some of it into heat, which is how they calm the reflections inside a room. For the same reason, they barely change how much sound the wall behind them lets through to the other side.

Treating a room can take a few decibels off the build-up of sound inside it, and the neighbours hear those few decibels less. A wall, a door or a ceiling built to isolate is measured in tens of decibels. Those tens of decibels come from how the room is built: heavy layers, no gaps for air to pass through, and linings held apart from the structure so that vibration does not cross.

Bass is the hardest part to keep in. Its long wavelengths pass through light construction far more easily than treble does, and a subwoofer standing on a floor or against a shared wall can set the building itself vibrating. If there are neighbours, ask about isolation before you buy subwoofers or decorative treatment, not after.

Isolation is building work

How much sound a room lets out is settled by what its walls, floor, ceiling, doors and windows are made of and how they meet. So it is cheapest to get right while those are being built or rebuilt. Adding it to a finished room usually means taking finishes out again, and costs several times more than designing it in. Where isolation is needed at all, it can become the largest cost in the project, and its largest risk.

Sound also finds the ways round a wall: along the structure, through ducts and ceiling voids, under a door. These flanking paths are why a strong wall on its own can disappoint, and why an isolation study follows the whole route from the source to the neighbour rather than one partition.

A limiter belongs to the same study. The study tells you what level the building can take; a limiter, set at commissioning and locked, keeps the system to it whatever happens to the volume control.

Where the room and the system meet

The room and the system are separate problems, but you hear them together, and they meet in the bass. In a small room, the room modes decide much of what the bass sounds like at each seat, so where a subwoofer stands can matter as much as which one it is.

DSP then corrects what is left. EQ evens out the level of each frequency at the listening positions, and time alignment makes the speakers arrive together. But room correction works on the signal, not on the room: it cannot shorten a room’s reverberation or fill a deep null. It comes after treatment, not instead of it.

That is why, in how we work, the room comes before the speakers. The listening room was built in that order: panels, corner traps and active bass absorbers first, then measurement and tuning across the sofa.

Which one do you have?

  • Room acousticsVoices blur when the room is busy, people raise their voices to be heard, the room sounds hard or rings on, or one bass note booms.
  • The sound systemThe sound changes a lot from one table to the next, the system strains or distorts before it is loud enough, or the speakers and the subwoofer never seem to agree.
  • IsolationThe neighbours complain, the street comes in, or you cannot play at the level you want during the hours you open.

Most rooms have more than one. Name each, and expect a separate answer to each: a proposal that offers one fix for all three is a warning sign. Before you ask anyone, read what to ask a consultant for; the terms used here are in the glossary.