I've always thought that using thicker panels (rockwool with 3,75 lb density in my case) is always better even for first reflection points. But after comparing 3" to 4" absorbents on sidewalls, I'm not so sure anymore. Yes I get a bit more bass absorption with the 4" rockwool panels, but it also sounds more boxed in. Actually it sounds more open and airy with the 3" absorbents. I haven't tried 2" panels yet.

But what's you recommended thickness when it comes to treating first reflections on sidewalls, frontwall and ceiling? Is it actually better to use 2 inch panels and have basstraps at other places?

I should mention that I have 8 bass traps in the room.

I can't see why using thicker panels should change the sound at midrange frequencies. It should just extend the absorption to lower frequencies. Have you tried measuring to see if you can correlate what you hear with actual numbers?

--Ethan

Not sure if this is saying very much. Two first pictures with 3 inch panels on sidewalls and the two last ones with 4" panels. Unsmoothed.

Wasn't able to load the image. Here are the links:
3":
http://www.hifisentralen.no/forum/index.php?action=dlattach;topic=39668.0;attach=112937;image

http://www.hifisentralen.no/forum/index.php?action=dlattach;topic=39668.0;attach=112939;image

4":
http://www.hifisentralen.no/forum/index.php?action=dlattach;topic=39668.0;attach=112941;image

http://www.hifisentralen.no/forum/index.php?action=dlattach;topic=39668.0;attach=112943;image

Interesting. There are small differences in the comb filter pattern at higher frequencies. Is there any chance the microphone was not in precisely the same place for both tests? Even moving the microphone one inch can account for changes that large.

--Ethan

The microphone was at the exact same postition. I'm having a hard time to decide which I prefer though. It depends on the music. To mye ears, there is a distinct difference.

Bryan from GIK was telling me somtething about that the thicker ones gave a little more bottom end control, but more midbass too without enough bass control to balance it on the reflections.

He didn't recommend using thicker panels on sidewalls or on other first reflections, but only thicker basstraps other places.

But you disagree? Thicker at all places are beneficial?

I would also like to ask where you use panels that absorb all the way up in your room. Seems like you mostly use basstraps that start reflecting in midrange. I've seen that you use panels that absorb all freq at the sidewalls, but is that the only place?

Yes, my standard advice is for all absorbers to be thick, even at reflection points. You don't need thick absorbers there, because early reflection are mainly a mid and high frequency issue. But more bass trapping is always welcome.

--Ethan