I'm using a pair of Kappa 9's with dipole midranges (midrange back shooting backward) and a bipolar tweeter shooting backward toward the wall. The room is about 14x18 with the speakers on the 14' wall about 9 feet apart and each speaker about 2-3 feet from either wall.
Formerly, I had been using monopolar speakers and per the advice of many experts here, I treated the entire front wall or the majority of it with 4 2'x4' OC703 1" panels. However after upgrading my speakers to bipole/dipole speakers, the ambience of the speaker and the room seem rather dead. I suspected as such I was absorbing too much of the backwave from the speaker (I know is desired in HT). So I took down the 2 panels directly behind the speakers (they are the two panels closest to either side wall), but I had left the panels on either side of the TV (the panels closest to the center). After listening to music and judging with my own ears, there was clearly more richness and ambience to music and while the center image seemed only a tad less focus, the soundstage grew by a bit, which I preferred for music (unpreferred for HT).
So down to my question, should I play with diffusion directly behind the speaker rather than absorption. Seeing that my room is relatively small, I'm not sure leaving it bare is really an option acoustically. Unfortunately I don't have any ficus plants to play around with to position behind my speaker. Or should I just use diffusion on the entire wall for music? The occasional movie will be played but it is not of primary concern. I also have 2x4 oc703 panels at the first reflection point and will definitely use diffusion behind the main LP when I get the chance.
After doing some more research on the matter, perusing 1D QRDs and 2D diffusors, I've stumbled upon a most novel solution a polycylindrical diffusor. From my understanding you of all people would probably recommend a 1D QRD to diffuse horizontally rather than dissipate energy into the ceiling or the floor. So ideally a 1D QRD is ideal, but I have read that a polycylindrical diffusor would be ideal in the sense that it can diffuse just as well horizontally if there was enough distance from the listener to the diffusor which is not a problem if the diffusor were to be placed on the front wall.
However, behind the LP, I will use a traditional 1D or 2D diffusor. Has anyone accomplished a polycylindrical diffusor? I'm reading on the subject and it's rather confusing to extrapolate measurements for one to DIY. I'm getting things such as a "half sine wave," angle of incidence of 30 degrees. If anyone can clarify that'd be great.