[Sheldon N]

I've recently changed up my desktop audio system and I'm having issues with bass resonance at around 130hz. I think it's due to boundary reinforcement from the near wall behind the speakers so I was going to add a panel behind my monitors to try to help tame it.

What sort of material should I be looking at for a panel in this configuration? I'm probably going the DIY route but I want it to be as effective as possible. Should I do a dense Rockboard 60 or 80 or perhaps a 703 FRK? Any thoughts on either 2" or 4" thick, and air gap vs just a thicker panel? Likely panel dimensions are going to be 2 feet tall by 7 feet wide (long horizontal strip behind monitors).

Any suggestions would be welcome!

Here's a couple pictures of the room setup. Speakers have changed since this was taken, currently using Dynaudio Excite x12's with foam plug installed in the rear ports.

[Rob Babcock]

Welcome to AC!   I'd suggest either Rock wool or Owens Corning 705 Rigid Fiberglass Board as good materials to start with.

[Ethan Winer]

I'm having issues with bass resonance at around 130hz. I think it's due to boundary reinforcement from the near wall behind the speakers so I was going to add a panel behind my monitors to try to help tame it.

Any of those materials you mentioned will work fine if they're thick enough. But the problem you describe is not caused by what you think. First, reflections from a nearby boundary create peaks and nulls, but not resonance. Resonance is due to the room itself. Second, a peak at 135 Hz caused by a boundary reflection occurs 4'2" away from the boundary. It's clear from your photos that your speakers are much closer than that. So the proper solution to your problem is bass traps placed in corners rather than behind your speakers.

You'll also get better bass if you set up so the speakers fire the longer way down the room. I suggest you put your speakers in front of the window at what's now your right side wall, and move the furniture away from the corners to make room for bass traps.

More here:

Front Wall Absorption
Frequency-Distance Calculator
How to set up a room

--Ethan

[Alex Reynolds]

I've recently changed up my desktop audio system and I'm having issues with bass resonance at around 130hz. I think it's due to boundary reinforcement from the near wall behind the speakers so I was going to add a panel behind my monitors to try to help tame it.

What sort of material should I be looking at for a panel in this configuration? I'm probably going the DIY route but I want it to be as effective as possible. Should I do a dense Rockboard 60 or 80 or perhaps a 703 FRK? Any thoughts on either 2" or 4" thick, and air gap vs just a thicker panel?

Ethan is correct up above. The resonance is probably not due to SBIR, but the rooms size. Typically, the problems associated with SBIR are strong nulls. Peaks come sometimes as well, though are usually not too severe. More on SBIR here: http://gikacoustics.com/speaker-boundary-interference-response-sbir/

I would also advise facing the short wall, but you really wouldn't have a spot to sit your couch behind you if you were positioned that way (unless the closet could be blocked by it without causing too many problems for you).

If you're going to DIY you should do at least 4" thick of full absorption, if not 6" thick. I usually recommend fully thick corner treatment as well. Superchunks or soffits for the front corners, first reflection points with 4" panels (air gap if possible as well - and don't forget about the ceiling), and thicker treatments on the back wall if possible (~6" thick at least if possible)

[Sheldon N]

Thanks all. I don't think I'm able to rearrange the desk to the long side unfortunately. It just wouldn't work with the strong backlight coming in from the window and from the sun position. I work at home so this needs to be functional/comfortable for the long haul, I spent 10-12 hours a day sitting in front of the screens here and the music is usually just low volume listening.

There's not much space for corner traps given the window and filing cabinet on the back two corners.  The closet on the left side of the desk is actually already a pretty good bass trap itself if I open it (full of lots of soft goods, floor to ceiling) and I need to retain access. The other rear corner is actually a double wide 45 degree angled doorway which is open much of the time.

I'm planning on putting up a couple canvas prints and hiding some dense acoustic insulation behind them, which might help a tiny bit with low frequencies, but really the only place I can easily put a largish absorber is behind the monitors.

I guess my main question is... given the space constraints and the location of the absorber, what materials would you recommend to use? I had thought about 2" 703 FRK, but was also considering 4" of Rockboard 60. Mainly looking to figure out what will give me the best performance overall or the best bang for the buck.

[Rob Babcock]

Yeah, very true.  I was in a hurry and wanted to approve your post, so I basically just answered half the question.  Peaks and nulls are room effects and often are more easily ameliorated by placement.  That said, adding some broadband absorption often helps a room in many ways.

[Alex Reynolds]

Would definitely go with the 4" material. The thicker it is, the lower in frequency you'll get absorbed, so the better off you'll be. I still recommend treating the front corners and first reflection points along with the back wall regardless of which way you're set up.

If the back wall panel could be 6", the corners at least 4", you'll get pretty decent absorption down to 100 Hz.

[Sheldon N]

So I had some extra cotton fiber insulation laying around and I've put some behind the speakers/monitor just to test what effect that would have. I notice a marked improvement in the problem, cleaner/clearer bass with less of that resonant ringing midbass. I still need to find a local source for rigid insulation and then build a proper 4" panel, but at least this is an early indication that it should help the problem. I've also got a couple canvas prints that I'm going to hang on the walls that have a 1" space behind. I'll probably put some insulation inside those too.

Thanks all for the help!