Why is the resonance panel bigger than the other two?

Because corner loading needs area. The reflection and reverberation panels are 300 mm square; this one is 600 mm square and 43 mm deep, and the size is the mechanism rather than the packaging.

The panel works on pressure, and pressure acts over an area. A small panel in a corner is in the right place with too little of itself there to matter. Scaling it up is not a way to sell more material: it is what makes a shallow panel able to do low-frequency work at all.

The counter-intuitive part, and it is measured

This panel gets better at the bottom and worse at the top when you put it in a corner. Two things are happening at once and they pull in opposite directions:

• At low frequency the face is pressure-driven, so a boundary loads it harder. More boundaries, more work: away from the walls, against one wall, in a corner against two: the absorption at 125 Hz climbs at each rung.
• At high frequency the face absorbs nothing at all. The only absorbing material the room can see is the narrow band around the panel's edge, and putting it in a corner hides two of those edges. So the top of its range falls as the bottom rises.

The two effects cross at 500 Hz. Below that, corner placement is a large gain; above it, a small loss. Which is exactly the trade you want from a device whose job is the bottom octave, and it is why the panel is specified in the corner and measured there.

One consequence worth stating plainly: this is not a broadband absorber and must never be sized as one. Its job is the axis that booms.

What to read next

What happens if the corner is not available. Then the Resonance Control Panel.