DIY bass absorbing panels behind speakers

Dear Naim forum users,

a couple of months ago I had to move my Hi-Fi system to a new room. I’ve been struggling to get a properly good and balanced sound, luckily things improved a lot after changing the listening positioning, adding some acoustic panels and changing many little details.

After all my efforts, I noticed that the bass is still strongly reflected by the wall behind the speakers, thus making all the mids and soundstage muddy and dirty.

I tried to put 3 raw polyurethane panels like this one:

Suddenly I got a much bigger and precise soundstage which is fantastic. On the other side the bass seems too clean now. I can feel that the speakers still go down properly and that bass is more articulated, however it’s less punchy and engaging (both with music and movies).

In many Hi-Fi system photos some of you have put absorbing panels behind the speakers (usually with similar speaker height). What did you experience? Is there a suggested size to get a balanced result without exaggerating things? Or should I choose a less absorbing material? Also I wonder when this effect should be considered too much, I have no real comparison other than the experience with my own speakers. Quite hard to judge without a proper reference, so is it just a matter of taste?

I’m looking forward to hearing your thoughs on this. Thank you very much in advance for any advice.

Some photos I’ve noticed in “System Pics 2023”:

I’ve had similar issues with Bass, the three things that have done to help are firstly the bass traps in the corners (you can see them in the photo) - I used GIK sofit floor to ceiling in each of the 4 corners, this really cleaned things up. The next major change was when I went from a 300 to nap 500 - I appreciate this isn’t always an option but the extra control it had over bass really helped get rid of uneven bass. Lastly it’s been moving the speakers and toe in - this has helped a little although doesn’t eliminate a stubborn bass node I have around the seating position.

The absorber behind the speaker has helped a little but it was quite subtle and the trouble with bass in lower frequencies is that it needs quite a thick absorber to make a difference and I’ve concluded it will not solve my Roon node. One trick I’ve found is to play a single frequency tone (you can find them on the streaming services) which has helped isolate the exact frequency causing the issue and location.

Good luck!

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I added the panels behind my speakers (and on side walls, at first reflection points). I had also, previously, added sound absorbing panels to the ceiling. The panels behind the speakers definitely helped remove some of the bass boom, but it’s a work in progress. At my dealers on Friday using the same system as mine, I thought that the bass sounded much tighter and punchier than in my room. I might investigate the active bass traps or look at the Gaia sound absorbing feet (I have a suspended wooden floor).

But for me, the panels were an improvement from where I was before, for sure. Worth investigating.

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@Wealdmuso my first acoutic panels made the mids and highs more clear, but bass was still too much in my opinion. I have no doubt that a better amp would give better control, but it’s a room problem in the first place whether I use my Hi-Fi system or another one.
I’ve been moving my speakers a lot and toed them in as well. Now I think I found a very good and balanced spot.

Did you use REW? I thought of using it but I can’t find the USB calibrated mic they suggest, so I’m stuck with that. I’ve used the Focal tools CD to see how the frequency response is. It seems decent across the bass spectrum, but below 80 - 100 Hz the volume seems around 10 - 20 dB less than higher frequencies (I measured it with a phone app, I know it’s not precise but didn’t have another option).

@BobbyYork it seems we both have a work in pregress! What’s the side size of your panels?
I wonder how the room of your dealer is, maybe he’s using bass traps or maybe the wall has less reverberation. Have you already tried to put your speakers closer to the wall behind and see how the bass change?

Hi Blacknote
I use GIK Tritraps in the front corners and a couple of monster traps for the window behind my listening position. I have a couple of DIY panels I use for first reflection points.
The bass is still a little uneven on some tracks and albums so to improve this I probably need more bass traps.
I have some additional 100mm rockwool bats that I wrapped in weed suppressing membrane (to keep the fibres in check) and have been playing around with positioning these to see where they work best.
I’m not sure I like the effect when positioned behind the speakers and with some positioning around the room the highs and mids can get a little overdamped. This is where range limiters or additional diffusion might work better.
I am about to download REW and order a DSP UMIK microphone (readily available on the internet) and will take some measurements or will give it my best shot (not very techy). There is lots of info and video tutorials to follow so I hope I can get the job done.
Will let you know how I get on.
Stu

@StuW My bass is not perfectly uniform, I need to work on that, but I think I’m close to get a really good result even without measurements (in my opinion).

My DIY acoustic panels do not influence the mids and highs, they basically absorb the lower end; these panels are commonly used to stop noise from coming inside a room and are installed under the floor or behind a plasterboard. Nothing refined but they do the job surprisingly well. My soundstage and mids seem to shine and are very clean. Have you considered using a different material other than rockwool? I also noticed that if the absorbing panel is higher than the loudspeakers, the mids get cleaner.

The DSP UMIK is not available from where I am, are you buying the mic directly from the factory? Maybe I should try that way.

Let me know how it goes with your setup, I’m sure it’s worth the effort. By the way, your guitars look great, they inspired me!

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The bass in my room was slow and lacked definition. I used bass traps in the four room corners but bottom end was still unsatisfactory. The solution in my room was to add 16-inch ASC tube traps along the wall between the speakers. This added additional bass absorption and diffusion on the front wall–bass was tightened up and became much quicker and sound stage also improved. While there’s still some very- low frequency suckout at the listening position, this is vastly better than the slow muddy bass that previously existed.

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