Why the Reflection Control Panel's absorption figures look low, and why that is the point

Because absorption is the wrong measure for it. The Reflection Control Panel is not an absorber. Its job is to redirect an early reflection, not to remove energy from the room, so a low absorption coefficient is the panel doing what it is designed to do. A high absorption figure on this panel would mean it was doing the wrong job.

And there is a measure that is the right one. The goal is to take a reflection that is audible as a separate arrival and make it inaudible. That threshold is published research, not our assertion: Olive and Toole's 1989 AES paper on the detection of reflections in typical rooms establishes how far below the direct sound a reflection has to sit before a listener stops noticing it, and how far below depends on how late it arrives. A reflection at around two milliseconds needs only a few decibels of separation. By twenty milliseconds it needs roughly a dozen. The design grades every loudspeaker-to-seat bounce against that curve, per frequency band, and the amount by which a reflection exceeds the line is the amount of work to do.

So the panel is not judged on how much it absorbs. It is judged on whether it brings the arrivals under the line.

Why splitting a reflection works at all

A single reflection is one loud, coherent arrival. Break it into many smaller arrivals, spread slightly in time and direction, and each one is individually further below the direct sound, and each is later, which is the forgiving direction on that curve. The reflection has not been removed. It has been made unrecognisable as an event, which is what the ear was objecting to.

This is also why the room does not go dead. Absorbing an early reflection solves the same problem by taking the energy out, and a room treated that way loses the sense of space along with the smearing.

Two curves, not one number

The published absorption chart for this panel plots two series, and they are not two versions of one figure. They are the two ways the panel can be fixed. Bonded with adhesive, the panel is damped and stays rigid, absorbing little and scattering cleanly: that is the specified condition and the one every design uses. Screwed without adhesive, the panel is free to flex and adds an absorption peak of its own, which reads as a higher number and is not the condition designed for. Both have been published for years.

A note on the word "diffusion"

You will see it used loosely for anything that is not an absorber. It has a specific meaning: a scattering coefficient measured to ISO 17497. We have not measured one, so we say what the panel does (it scatters early reflections rather than absorbing them), and leave the word alone. Nor is this a true mathematical diffusor, and that concept has limited application in a small room in any case. If a supplier claims diffusion, ask which standard and what the coefficient is.

One thing worth knowing about the measurement most people reach for

A peak read off an energy-time curve is the obvious way to judge a reflection, and it under-reports one that is poorer in high frequencies than the direct sound by a substantial margin, around twenty decibels in the published work. That is exactly the case in a real room, where loudspeaker directivity and boundary absorption roll off the reflection's top end. It is the reason a reflection is judged band by band rather than as one broadband number.

What to read next

The measured data itself. Then, if you are specifying a room, the design service.