What reverberation is, and what actually fixes it

Reverberation is the sound still in the room after the source has stopped. Clap your hands in a bare room and the tail you hear is reverberation: energy bouncing between hard surfaces, arriving late and from everywhere at once. It is measured as reverberation time (how long sound takes to fall by 60 dB), and in a small, hard room it is what makes dialogue difficult to follow. The voice arrives, and then the room repeats it.

What fixes it is broadband absorption, spread across area. The Reverberation Control Panel is a 50 mm acoustic foam panel that absorbs across the mid and high band, above roughly 200 Hz. It is fitted across broad areas of wall and ceiling, checkerboarded, weighted toward the rear of the room, and around the surround speakers. Porous absorption of this kind does depend on depth: that is general acoustics, and it is why this panel is weak at the bottom of the range and is not the panel for that job. What it is not is 100 or 200 mm deep, and that matters commercially: treatment depth comes out of the room's usable dimensions, and in a high-end room the floor area a deep system consumes costs considerably more than the treatment does.

What it will not fix is bass, and that matters more than it sounds. A thin broadband absorber has a weak low-frequency tail. Uneven, boomy bass is resonance, and resonance is a different mechanism with a different answer.

Reverberation is one of three problems, not the whole of it

Every acoustic complaint about a small room comes back to three things: reflection, resonance and reverberation. They are separate problems with separate mechanisms, and a device that answers one does not answer the others. Early reflections arriving audibly after the direct sound are a reflection problem. Bass that is uneven from seat to seat is a resonance problem. Decay that runs too long across the mid and high band (the echoey room, the dialogue you have to work at) is reverberation.

C-ATS is built on that decomposition: one engineered panel per problem, each at 50 mm or less, sold and specified as a system rather than as a shelf of panels. So the useful first question on a room is not which product to buy. It is which of the three you actually have, and usually it is more than one.

What reverberation time we design to

These are the targets C-ATS designs to. They are not quoted from a standard (no standard sets a single number for a private cinema), and other designers work to slightly different ranges. We publish ours so you can see what we are aiming at.

• A dedicated cinema: 0.3–0.5 s.
• A critical listening room: 0.3–0.5 s.
• A multi-purpose media room: 0.4–0.6 s.
• A control room: 0.2–0.4 s.

Why one reverberation-time number hides the problem

A room can hit 0.4 s overall while its height axis sits well outside that, and it will still sound wrong. One figure averages away the axis that is out of line, which is why we set a target on each of the three axes and design for the three to agree. Flatness across all three is the goal; a single headline number is not.

Where the room's surfaces are working against you

The commonest version of this on a real job is not a shortage of panels. It is a mismatch between the surfaces themselves: a carpeted floor under a plasterboard ceiling cannot be balanced with panels, however many are added, because the two surfaces facing each other are so unalike. The fix is in the construction rather than in the treatment: a hard perimeter walkway in wood around a carpeted seating area brings the vertical axis back into range.

The same logic applies downwards. For deep bass, the answer is a wall built properly on isolation mounts, not surface traps: at 30 Hz a surface device cannot do what the construction does. Build first, then treat, in that order, because the second cannot rescue the first.

What to read next

The three problems and the one panel each. Then the measured absorption data, if you want the figures behind the panel before you specify it.