Hi Mar,
You can use a simple mirror to determine your first reflection points for your panels. Just slide along the each side of the room to see the reflection points for each speaker. You will note that the left and right speakers on each side of the room have their own respective reflection points, and ideally, you have a panel at each point on each side for each speaker.
Regading the panels you ordered from AcoustiMac, the "acoustical panels", are sound-absorbing, and are best for attenuating and mitigating slap echo, but they won't do anything to add diffusion, and thereby life and sparkle to your room. I've found I don't need much of these as my space is pretty heavily furnished (see photos below). I do have a panel from AcoustiMac on a wall that separate my living space from the kitchen area and above a large picture window that is an "outside" wall.
I'm going to go out on a limb and guess you will find the GIK Acoustics Impressions panels will provide the most notable and enjoyable improvement. I was kindly gifted 8 of the GIK Acoustics Alpha 4A panels and 4 GIK Polyfusors by a local AA member, and its turned out the Alpha 4A panels have brought, by far, the biggest improvement. I originally put all four Polyfusors into my well-furnished "room" and it sucked all the life out of the presentation. So, now, I only have one, in 1 corner of the space. The other 3 are presently sitting unused in the spare bedroom.
The Alpha 4A panels, OTOH, really bring a very nice improvement, and I've now got 5-6 of them in the room. I'm still playing around with placement with some of the remaining 4As but I have two along the "front wall" (which in my case is a half-wall, one at a reflection point in the window behind the couch, and two in the corners between the outside wall (near the big window) and the corner of the half-wall on top of the REL sub.
You've probably read what the Alpha 4A and Impression panels do, and I really like the improvements they bring. They are intended to provide both some diffusion and liven up a room, and they do this in a very nice and natural-sounding way. They make the presenation more spacious, lively, and "focused" in a very good way, and they also improve the imaging of the stereo sound field.
There is a technical paper on what they do on the GIK web site on Decoding Diffusion:
https://www.gikacoustics.com/decodin...tic-solutions/
I'm using the linear 1D panels, 4" deep as that is what I was kindly given by Keith.
Here are some pics to show you how I am using the Alpha 4A diffusor panels.
The main rack and the Harbeths. You can see two the panels on the half-wall behind the main rack.
A wide-angle view, showing the panel on the left at a first-reflection point. You can also a see an AcousticMac acoustical panel on the wall near the celing and above the couch and window.
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Behind the right speaker:
Behind the left speaker:
