Room mode compensation?

[Steve Conner]

Hi all,

I'm writing to ask for your opinions on room mode compensation.

The acoustics in my living room have always sucked. I got the upper frequencies under control with some rugs and wall hangings, but the bass is still dreadful.

Lately I did some research, and discovered that the room has two plastered brick walls on opposite sides. Brick is very solid, so it doesn't absorb bass, and rugs and drapes don't either. The speakers are against one brick wall, and the couch is against the other, so the conditions are just right for a big standing wave. I can't really move them, because the couch is too big to fit against the non-brick wall.

So, I experimented with a parametric EQ, and found that if I cut 8dB at 60Hz with a Q of 3, the problem was solved! Bass never sounded better. Also, the 60Hz figure agrees with theoretical calculations from the distance between the two brick walls. There will be other modes, but just notching this one made a huge difference.

So the question is, what to do about it? Why should I bother building bass traps, and having them take up room space, if I can just EQ it? And, what should I EQ it with? I don't really want my parametric EQ tied up. I could build a box with a stereo 60Hz notch filter inside. Or for about $150 more than the cost of parts for that, I could get a Behringer DCX2496, and have lots of other cool features besides EQ. None of which I need.

[Don Moose]

I could get a Behringer DCX2496, and have lots of other cool features besides EQ. None of which I need.

None of which you've tried. Not that I've looked at what they may be

+150USD for a neat toy or the experience (and hobby-resume item) "Acoustic Analysis and Compensation - Found 60Hz standing wave in main listening area and built -8dB Q=3 notch equalization unit to correct.

-- given the way character sets cross borders, I need to ask if you meant USD (the symbol I get), UKP or Euro.

Hope this helps!

[Enzo]

If you can simply EQ it out, then why indeed build bass traps?

MY first thought was also a cheap Behringer processor. So what if it has extra features? WHy gripe that your aspirin also works on sore muscles when all you have is a head ache?

But there are other units than a new Behringer, an older used two channel - or more - parametric unit can be had cheap - probably from a guy who bought a new Behringer.

[eschertron]

You can save the headache of installing new equipment, and avoid the clutter of bass traps, by knocking a hole in one of the brick walls and building a Helmholtz resonator on the other side

... but yeah, if you can sculpt with EQ, why not?

[Tom Phillips]

Steve,
Now that this old thread is back on the top of the stack I'm curious what approach you decided to use to solve your excessive bass problem?
Tom

[bob p]

The way that people design listening rooms has always confused me. Most of the purpose-built rooms that I've seen have been intentionally furnished in a minimalistic way, with virtually nothing that works for absorbing LF standing waves, and that ends up requiring ugly looking bass traps to eliminate the problem. In some respects, I think that the HiFi shops bring this sort of problem upon themselves by designing rooms the way that they do. It's almost as if they show you how to design a room in a way that requires you to buy bass traps.

I once lived in an apartment that sounds like what you're describing -- it was a 1920s high-rise that was brick, concrete and plaster with parquet wood floors. It was a very live sounding room and I never was able to tame the HF response or the standing wave thump. EQ would have been a great approach to the problem, but I didn't have access to that sort of thing in the 80s. The only options then were to try to redecorate, which isn't the most practical approach. Back then my living space didn't have heavy draperies, wall-to-wall carpeting, and a room full of big fluffy couches, and padded chairs. I was never able to tame the sound problem.

Things are different now. I have zero problems with shrill highs or standing bass waves in our place. For entirely different reasons the room is stuffed to the max with the kinds of things that absorb bass signals. Shrill HF and standing waves aren't a problem. But then I'm not sure that it's all attributable to decor, as the living space is kind of a funny shaped room, sort of an open design, with huge wide geometric arches at each end, open room dividers, and huge disappearing dividers that can be used to change the room size. It's pinnacle of the "open" 1950s suburban architecture in the US. HiFi was a big deal back then, so maybe the architects were thinking about standing wave problems and intentionally designed to eliminate it. I had never thought too much about it. In fact, I had always thought that the room was disadvantaged because there was no symmetry in the walled surfaces, but now that I think about it, the the frequency response has always seemed surprisingly flat. I was surprised when I ran a spectrum analyzer and it said that I didn't need the 1/3 octave EQ that I had bought.

Now that I think about it, I think that one of the advantages of "modern" architecture is that the basic room design can help to eliminate the standing wave problem. If your living space is a perfectly shaped 6-surface vault, that could be a real problem EQ might be the answer, but then stuffing your place with comfy things that appeal to the gals more than the guys can be a surprisingly good approach. One thing about bass traps, they're ugly. If you can find a better looking approach, I'd go that way first.

[Leo_Gnardo]

I think that one of the advantages of "modern" architecture is that the basic room design can help to eliminate the standing wave problem. If your living space is a perfectly shaped 6-surface vault, that could be a real problem EQ might be the answer, but then stuffing your place with comfy things that appeal to the gals more than the guys can be a surprisingly good approach. One thing about bass traps, they're ugly. If you can find a better looking approach, I'd go that way first.

Good observations! And bass traps need not be ugly and obvious. They can be if added to a pre-existing room, but those with the $$$$$ can build a purpose-built room with a proper designer who can predict problem frequencies and provide built-in solutions that don't offend the eye. This is more the domain of professional studio control room and auditorium designers like John Storyk.

One of the first-order "fixes" to pre-existing rooms is to un-parallel the walls, also the ceiling if possible. Parallel walls are one of the main offenders in creating low frequency room ring modes. One need not lose lots of floor space. The walls can be built-out with narrow wedges, no more than say 6 inches thick, and staggered from side to side. I recommended this solution for a rehearsal room, and it changed it from a honking wreck into a decently usable space. Far from perfect but a couple days work and at the time a couple hundred dollars of studs and drywall did the trick that hanging carpets and other low-impact fixes could not. With a number of sound-sources going at once, it was impossible to apply appropriate EQ to each. This was @ 1990 when dirt-cheap Behringers weren't yet available.

Furniture, carpets, wall hangings, foam wedgies, all good stuff, and they do sort out echoes mostly above 100-120 Hz. Below that, it's the room.

Or you can staple a couple thousand egg boxes to the walls & ceiling - - - - - JUST KIDDING!

[Tom Phillips]

...Or you can staple a couple thousand egg boxes to the walls & ceiling ...

When suggesting such solutions I think it is important that we adhere to the proper technical terminology. Your suggestion is properly known as the "Hee Haw acoustic wall."
Merry Christmas,
Tom