That has been on my bookshelf since the Second Edition.
And I can't recall any instance where it was ever recommended to manage reflections by using REFLECTORS. Diffusion and absorption, yes. And even varying degrees of absorption to suit one's tastes. But not reflectors.
Keep in mind that this is what you wrote that I was responding to:
Well, you question the use of the phrase "reflective panels". Well in my brief description I use this word to describe how you are managing reflections. I go on to say that these are to be managed by using different materials (meaning of course, for absorption or diffusion).
Here is what I wrote:
To manage those reflections you can use reflective panels in the centre of the walls and in the centre of the ceiling. These are ideally replaceable with panels of different materials and also these panels are to be adjustable for angle.
As you can see I was writing in the context of reflection, so the use of the term "reflective panels" is really reasonable and sensible in that context.
Steve, you go on to write:
Can't think of any instance where it would be required it be reflected rather than diffused or absorbed.
This is referring to these reflections of course.
Unfortunately this is a repetition of a myth concerning creating an ideal acoustic in a listening room.
If you do not plan and manage reflections in your listening room but absorb and diffuse them all, you will end up with a very small soundstage. Trust me, I have done this myself.
Every acoustic engineer who you might wish to speak to would tell you this is their experience and they would follow that up with a discussion about the importance of managing reflections.
You can of course manage reflections with different levels of diffuser/reflector, and of course this is what I pointed at in my initial posting.
I would like you to have a look at the following diagram:
This is from a website for a company that creates a product called a "Tube Trap". When I created the acoustic treatments for my listening room I would have loved it if I could have had these.
With considerable simplification I will write that each Tube Trap is a column with an absorbing side and a reflecting side.
Tube traps can be used for the three basic categories available to the acoustic engineer, diffusion, reflection and absorption.
In the above diagram you can see that the Tube Traps are not simply all used to maximise diffusion and absorption, instead they are deployed carefully to managing diffusion, absorption and reflections.
In the simpler system I described for my own room I actually describe managing the minimum of reflections, merely those from the side walls, and in fact one from the ceiling.
Today an acoustic engineer in creating a listening room will work with many more reflections than this, and they will be using reflectors for that purpose. Now those reflectors might well be diffusors and absorbers for different frequencies or to create different levels of reflection, but they will also be reflectors. And when the engineer is talking about them in the context of reflection he or she will describe them very likely as reflectors.
I'm delighted to see that jaddie has included a quote from the Fifth edition of F. Alton Everest's Master Handbook of Acoustics
The internal treatments consists of the deployment of diffusors, absorbers and (whisper) reflectors. Some massive ones actually.