Do you have or tested such panel? I was often tempted.
You mentioned reverberation. Reverberation ( decay) should be no more than 1/100 of a second ie if your room doesn’t cater for this, there is only one way of dealing with this= treating your room with appropriate absorption/ diffusion products. Once this is in place the system becomes musical 
I had to deal with the bass issues in my troubled room first and it took 100 kilos+ of absorption materials to get the bass cleaned up to give you an idea. After that the midrange slotted in very nicely to only leave me with the issue of a slight high frequency lift to deal with- QRD and Skyline diffuser are appropriate for this, as it is often excessive front wall reflections causing the treble emphasis ( ringing or high reverb time).
As Thomas said, it is indeed a ‘journey’. It is fair to say that mine will be completed in just under a year and for the first time I am truly hearing, what my system is capable of 
ATB Peter
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I have 2 of these on order to go on my front wall ( glass door) to deal with a second reflection back to the listening position.Peter
When I treated the corners with the things I mentioned above, the sound has no reverberation anymore.
However I am not sure if the term reverberation is appropriate. My problem was a not always clean bass. It was a bit overwhelming , dirty and dragging on some tracks.
I have very heavy carpets on the floor and my speakers sit on finite elemente cerabases.
I feel all is all right, however I am wondering what diffusing panel would still ameliorate, or not.
I tried something like this Woodfoil Ab between the speakers and I didn’t like the effect. The sound was less lively.
It is diffusing and a bit absorbing too.
Peter, I copied your system from system pics, to better see what you have done. Your main problem is probably the windows ( glass) between your speakers. Am I righ?
Scatterer=diffuser. Diffuser is tge more common term - I just couldnt think of the word when I posted.
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This is a more up to date picture. It is poor simulation I am trying with an empty GIK box, but nevertheless it has diagnosed the secondary reflection, and as you say and not surprisingly the window is highly reflective. The 2 ordered panels are one metre square and will exceed the height of the speaker drive units by at least a foot. I am very much hoping they will do the trick, as the tonal balance of the room is now spot on to these old ears. ATB Peter
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If you get yourself a copy of REW (which is free), and a measuring microphone (the one REW recommends is just fine, a bit under £100 last time I looked), then you can look and see what your room is doing - my guess is a long decay time at the bass end, which adequate judiciously bass traps would be likely to clean up.
Also important not to forget the ceiling first reflection point.
You can also put panels in the windows and cover with curtains
.
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Exactly,.many forget about this.
They don’t have to be big,.but can contribute to a very big improvement.
Use double-adhesive tape,.to find the right position in the ceiling before you mount them firmly.
My two in the ceiling are only 110*25cm large.
Where I lived before,.it was a concrete roof.
The room was 33m2,.I mounted a wooden roof with 3cm air-gap between the wooden roof and the concrete.
That roof contributed to a very big improvement,.and besides,it was beautiful,.and it looked like a “normal” room.
/Peder🙂
Hi Folkman.
Looks as if you have gone to town as well. I am for the moment avoiding treating the ceiling, as according to PMC’s helpful rep Tom B. ( he has been here twice) the Facts perform very well off-axis. Ultimately it then boils down to keeping within the audible time-frame (1/100/ sec. ideally), which I am for ceiling reflections. As you suggest I have covered most of the glass up behind the listening position ( normal sized window), which Im sat 2.5 feet away from. On the window ledge I have a 60x120 Profuser diffuser panel rested immediately behind me+ curtains semi drawn. Also GIK tritraps in the corners on the back wall and one horizontal absorber on the floor out of sight behind the sofa. This killed a tendency for the sofa at times feeling, as if you were in a massage chair at certain frequencies.
Enjoy your lovely system Peter
Yes, in many carpeted rooms it is the closest reflection point. But the panels don’t need to be rectangular: for the ceiling I plan something like one of these (coloured or white to be decided):
You and @PeterR both have nice soeakers, by the way!
They look really arty/cool👍🏼 ATB Peter
I tried bass traps in every places, and didn’t liked the effect.
Have you tried acoustic curtains ?
Yes indeed, at my wife’s request I’ve had 2 pairs of underpants in said fabric tailored for me. ATB Peter
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I don’t know if you are joking or not. I know there are acoustic curtains available as acoustic treatment.
After reading a few posts, some of them in particular, I think there is something that has to be clarified: acoustics is based on science, and the way we perceive sound as well.
Buying Gik acoustics (Vicoustic, etc.) expertise isn’t that expensive and is a good way to do things.
But if one want’s to address its room acoustic problems by itself, buying stuff probably isn’t the best way to start.
If one want’s to solve its room acoustic problems, learning is key.
Learning/knowing basic things like how sound propagates through the air (in a spherical way or like a beam, depending on its frequency), what’s the relation between frequency and wave length, what’s sound pressure, what’s sound absorption, what’s sound diffusion (or scattering), etc.
… And of course understanding the first law of thermodynamics.
Also, one needs to be aware of some myths around acoustics and furniture.
- Bookshelves won’t diffuse sound. A diffuser is designed using mathematical sequences…
- You can’t absorb low frequencies (under 250 Hz) with foam or furniture.
- Plants probably enjoy music but won’t be of any help to address room acoustic problems
- etc.
Good start points :
Videos :
–> https://www.youtube.com/user/GlennKuras/videos
–> https://www.youtube.com/user/AcousticFields/videos
–> https://www.youtube.com/user/EthanWiner/videos
–> https://www.youtube.com/watch?v=KE-AQZGUXTM&list=PLyUIMiryImPja0TpkcPhtcRjMKS8Ih6Zw&index=9
Curiosity :
High efficiency sound diffusers:
–> https://news.ncsu.edu/2017/06/thinner-sound-diffuser-2017/
PSI Audio – Addressing low frequencies
–> https://www.youtube.com/watch?v=1bRz7yXiLNg&list=PLyUIMiryImPja0TpkcPhtcRjMKS8Ih6Zw&index=5&t=0s
Nice readings edited by the Ecole Polytechnique Federale de Lausanne (Federal institute of Technology) :
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Thanks for all these informations Tomser. I want just to point that the artificial plants that I put recently in a corner between the speakers improved clearly the sound. To my great surprise. My goal was only decorating.