Too Much Bass Trapping?

Kax · Post by **Kax** » Wed Apr 14, 2004 6:59 am

Hello All

I've finished building my control room and I seem to have a problem with not enough bass. I'm not sure if all of the heavy masonry has given me too much low frequency absorbtion or if it's my speaker position or what the deal might be. Any suggestions?

Thanks
Greg

Kax · Post by **Kax** » Wed Apr 14, 2004 7:02 am

Oh yeah....the internal walls are made of a layer 5/8" sheetrock over a layer of 1/2" soundboard. The exterior walls are either the cinder block foundation or just 5/8" sheetrock. All the cavities are filled with Owens Corning soundbat insulation, and just R-30 against the garage wall.

The speakers are Genelec 1030A's on stands. The stands are heavy steel that sit on steel spikes.

Post by **Aaronw** » Wed Apr 14, 2004 7:43 am

Do you have a sub? Maybe something out of phase? Have you run spectral analysis of the room yet? See if you have any spikes or dips in the frequency spectrum. I'm not sure about the 1030's, do they have any adjustments for lows or highs?? Are you playing back material for reference that you are already familiar with?

Just some food for thought...

Aaron

Kax · Post by **Kax** » Wed Apr 14, 2004 11:24 am

Well...I don't have any phase problems, and I don't have a sub. But the room's not that big so I wouldn't really need one I don't think. I haven't run any analysis on the room. Short of renting a pink noise generator and spectrum analyzer...got any suggestions about doing room analysis? I am a Mac user and I'm sure there's great free software for the pc for this...but alas.

The 1030's have tone controls...but it's all attenuation. I guess I could roll off everything but the lows...but I'd rather try and fix the room or my speaker placement before I get into that business.

Other than the lack of bass...the room sounds pretty great. Great stereo image and the mids & highs translate perfectly. I just have to compensate (guess) for the low end which is not too much fun.

Ethan Winer · Post by **Ethan Winer** » Thu Apr 15, 2004 2:36 am

Greg,

> I seem to have a problem with not enough bass. <

A lack of bass is generally caused by too little bass trapping, not too much. I see a lot of areas marked "insulation," but it's not clear if that insulation is behind the walls or inside the room. If you have no bass trapping in the room, and all the insulation is behind the walls, then there's your problem.

--Ethan

Kax · Post by **Kax** » Thu Apr 15, 2004 12:21 pm

Hey...now there's an idea! Yes all of the insulation is inside the walls. All of the wall surfaces with the exception of the two slot walls are smooth. I guess the first place to try traps would be at the wall/ceiling corners as these are 90 degrees everywhere except the front of the room. The ceiling is sloped from the front wall to just behind the mix position and then flattens out to parallel w/ floor in the rear 2/3 of the room.

Thanks Ethan!

Oldaudio · Post by **Oldaudio** » Fri Apr 16, 2004 2:21 am

Greg : I agree with Ethan. What is your ceiling height ? Is it sloped? What is it made of? What's above it ? Your L & W dimensions look like they are pretty close together. You may have some troublesome modes trying to stand right where you are sitting !
Thanks, Durff

barefoot · Post by **barefoot** » Fri Apr 16, 2004 3:57 am

Kax wrote:All of the wall surfaces with the exception of the two slot walls are smooth. I guess the first place to try traps would be at the wall/ceiling corners as these are 90 degrees everywhere except the front of the room.

Continuing with what Ethan said, and from what I can tell, you already have your traps. You just need to open them up.

If I'm reading your diagram correctly, I see basically three shells to your room - the outer green shell, the middle blue shell, and the inner red shell. This seems like overkill as far as sound isolation goes. What if you cut openings in the red shell to acoustically couple the room with the insulation behind it? Instant bass traps!

All you need to do is take a circular saw with a short toothed blade (able to cut metal in case you hit any drywall nails), set the depth to 1 1/8" (sheetrock + soundboard), and cut rectangular openings near the top, bottom, and lateral corners of the room. Cover the openings with cloth and you'll have excellent low frequency absorption.

Thomas

Kax · Post by **Kax** » Wed Apr 21, 2004 3:00 am

Thanks for all of the input guys! Yes barefoot you're reading the drawing correctly. It's a little confusing (and I didn't help much w/ my description) because the walls vary in their construction. But all around the room...the inner shell is just drywall. Basically from the inside of the room out you've got....

1/2" drywall---studbay w/ insulation---air space---studbay w/ insulation---soundboard---5/8" drywall---masonry or garage wall. The exact arrangement of the studbays varies a little because the rear wall and left wall have the soundboard and 5/8" drywall on the room side of the studbays....not on the masonry side

But yes...I could make cutouts as you've suggested. On the rear wall....the insulation filled studbay would be exposed and behind it would be soundboard...5/8" drywall..an insulated studbay...then the masonry wall.

On the wall next to the door you'd get exposed studbay w/insulation...air space...studbay w/ insulation...soundboard...5/8" drywall...airspace filled w/ insulation...masonry wall.

I'm not sure if even I can make sense of what I've just written here! But if you can...do the cutouts still seem like a good idea? I'm willing to start cutting if really seems like it will improve the room.

Thanks for your help!

Greg

barefoot · Post by **barefoot** » Fri Apr 23, 2004 1:07 am

Kax wrote:I'm not sure if even I can make sense of what I've just written here! But if you can...do the cutouts still seem like a good idea? I'm willing to start cutting if really seems like it will improve the room.

Greg,

I've illustrated some or all of the places you might cut your openings. These areas would work similarly for the front of the room.

Maybe John or Steve can give their opinions on whether they think this is a good idea?

Thomas

knightfly · Post by **knightfly** » Fri Apr 23, 2004 9:49 am

Right, those areas ARE just bass traps waiting to happen. Thomas' suggestion should work well - if you can stuff more insulation into those cavities as you're going, even better.

Your perception of bass may be at least partly (or mostly) due to positioning of your head and speakers relative to ALL boundaries (and to each other) - try putting up a commercial CD and moving around the room, including raising and lowering your head - this will give you a feel for the depth of change in bass response.

If your speakers are 1/2 or 1/3 the distance from floor to ceiling, or the same distance from two walls, etc, any or all of these will cause problems with modal response and skew your bass perception. Your head should also NOT be equidistant from anything but the two side walls.

Also, if you're up to it you might consider soffit mounting your speakers in those two symmetrical areas to the front of the desk - that will improve imaging and smooth out a LOT of your acoustic problems... Steve

dragonsound · Post by **dragonsound** » Mon May 10, 2004 3:57 am

perhaps your walls are not "non-vibrational" enough and bass is just transmitting through the walls themselves. if this is not the problem and /or you can't do anything about the wall, try using a different monitor system, one with controls for where it is in the room, close to a wall, one with extended bass or adding a sub. you will still have to check whether your mixes translate to other systems with enough bass once you make any changes.

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