Time for Scopus?
 

My listening room is a difficult space (20' x 9.3' x 8' with concrete walls and a cheap laminate wood over concrete floor) but GIK absorption has turned it from "unlistenable" to "not awful". Over time, I've actually reduced the number of absorption panels in the room, as I found using lots of them made the sound over-damped and lifeless. I now have about 9 or 10 panels (a mix of 242, 244 and monster), mainly at reflection points and behind my head on the rear wall, but with 2 behind the speakers at the front wall. I listen along the long axis, any changes thus far have been made by ear rather than measurement.

I recently moved the speakers further into the room (they're now about 4 or 5 feet from the front wall) and the sound has blossomed, with midrange and treble being better than ever and a real sense of space and life to the sound. However, it's exacerbated a REALLY sizeable standing wave problem and the associated bass boom at a certain frequency range. I don't want to move the speakers back because I'm enjoying the sound so much more in the new position, but at the same time when the problem note plays and excites the problem mode it's absolutely ridiculous.

Questions:
1) Have I any chance of taming this with more targeted narrow-band treatment, or am I expecting miracles?
2) Would the Scopus be a suitable thing to look at and if so how many am I likely to need?
3) I know I need to measure the room, but is there anything in particular I should look for to help isolate the problem? There's one thorny issue in that I don't actually have an easy way of connecting a PC to my system (no DAC, no pre) which adds a layer of awkwardness.

I've been skirting around the room issue for a while, but I feel it's time to try to improve matters if I can without breaking the bank. My system sounds better than ever, so if I could just tame this bass resonance (I don't need perfection!) I'd be happy.

There are experts here that will add more but in my opinion, with a room similar in size to yours, your resonance will strong around 30 Hz. There is little you can do to treat that other than changing the locations of your speakers and listening position.

My suggestion is to start with your LP at least 5' from the back wall. Then either follow the Sumiko grand master setup procedure or use the Cardas rules to locate your speakers.

In my experience, You really have to locate them based on the low end first and then tweak to achieve your best midrange etc.

Thank you. I think the resonance in question is closer to the 70 - 100Hz range, but I'll try to confirm that later. That said I fear you're right that I'll end up compromising on mid and presence to get the bass right.

LP is currently about 6' from back wall, and speakers are about 55" from front wall.

Certainly can't say for sure what frequency or frequencies are the culprit but the lowest (around 30 Hz) tend to make things vibrate in my room. Your room dimensions will have standing waves starting around 30 due to the length of your room. There are some calculators on line and a nifty visual one on the real traps site called modecalc. I suggest you try that and see where your first order standing waves are and were they may overlap. Free knowledge.

You didn't mention corner traps which are pretty effective at helping in the mid to upper bass regions. I think the Monsters help in that area as well. It is the less than ~70Hz range that is very difficult to treat.

Have you tried the golden triangle aka Cardas method to locate your speakers? Good place to start.

How far are they from the side walls?

What kind of speakers do you have? (on my phone I can't see signatures)

Using a CD of test tones and my ears as a measuring tool (I know, I know!) it would seem that there is indeed a room mode in the mid-30Hz but it's not really causing me significant problems. Much more annoying are peaks in the low-to-mid-70s, around 120 and (surprisingly) around 145Hz. The one at 145 is annoying in that it's well in the range of the human voice and can lead to some unpleasant effects (the first vocal notes in Chris Isaak's "Blue Spanish Sky" are the perfect example of that.) The one at 120Hz is not so much of a subjective problem other than adding a bit of "thickening", but the one at 70-something is a doozy. It strikes me that these are all roughly multiples of each other, but with a wavelength in the 15.5' range (for 72Hz) I can't link it to any particular room dimensions.

I don't have corner traps per se, but I have GIK monster traps in the corners and they've helped a lot. However, I've found that putting too much absorption on the front wall leads to a thinness through the mid-range that I find a bit unpleasant. I used to have a lot more absorption there, but I gradually removed it. I'm reluctant to add much more broadband absorption to the area behind the speakers for this reason.

The Cardas method doesn't work so well in my room as the width is too small and it leaves the speakers without any spread between them. I've found the shape of the Sonus Faber Elipsa Reds (my current speakers, crwilli) allows them to go very close to side walls without too much issue, but in any case I don't have a huge amount of room to experiment laterally. It made a much bigger difference with my previous Kharmas than it does with the SFs.

I shouldn't give the impression that this is my first attempt at fixing these problems, nor that I haven't experimented EXTENSIVELY with positioning. I've been in this room for 11 years, been through multiple sets of speakers and ancillaries, speakers have been all over the room, sound treatments have been moved here there and everywhere, and while it's all been a bit haphazard, I feel I have a good sense of how speakers interact with this particular room. These frequencies have always been a problem to a greater or lesser extent and have caused me much mental pain! Hence my question about a more direct approach.

Oh, I should also say that I experimented a little with room correction software a long time ago, and while it improved some areas I felt the system lost a lot of "magic". If I could just get rid of the most obvious booming using some acoustical treatments I'd be able to cope with normal bass lumpiness!

Honestly, I would use room correction DSP. You can set the parameters to cover only the low bass region and leave the higher freq alone. Something like Dirac would be perfect. It will leave the midrange and treble alone, thus preserving that "magic" that you have discovered.

If the problem popped up when you moved the speakers then it is for sure a speaker location problem (I am sure you know this). One problem is we never want to "create" a problem but I see why you moved them. I would recommend that the front wall (the wall in front of you) is treated. I am not sure what kind of room you have but I would go with a mix of the Scopus T70s and Monster Traps (with limiters). That combination will hit the 70 to 140hz range without a problem.

I did get your email but not 100% sure if you have room on that wall or not.

Hi Glenn, thanks for much for the response (that was quick!) The problem has always been there and audible (with these and every other speaker), but the move has made everything else so much better that those frequencies really stand out as a glaring problem now. So they've got worse with the move, certainly, but they're always there and have always been there. I hate this room in so many ways!!!

That front "wall" is mainly a window, with about 12 or 18" of actual wall on either side, and a window sill maybe 2.5' from the floor. Anything extra I might add to treat that space would be obviously on the floor under the window, but there'd be room for a few T70s. I think I'd struggle to fit in anything else at the front, but I could certainly replace the 244s that are in the corners there with Monsters.

I'm quite tempted to just pull the trigger on a few things and see how I get on. I'll be in touch.

Edit: the panels I have pre-date the flex-range/limiter option. That could very well make an important difference.

Yes the limiter can help a lot!!

If the problem was there before the speaker move then it might not be the front wall that is causing the problem. Just a test to try. Play 70hz (or close to it) through your speakers and walk from the front of the room to the back of the room, in a straight line. Then do the same thing side to side. And last and not least sit in your chair and stand up. If you hear the wave get louder and softer from any of these tests then we can start to nail down where the problem is coming from. Basically if it changes walking front to back then we want the T70s on the front or back wall. If side to side then the side ways and so on................................

Thanks Glenn. I'll do that little experiment over the weekend.