slat wall question

[igloo]

If I put a slat wall as proposed on the SAE site, do I leave the corners untreated, or should I build a structure that incorporates corner absorbers to the slat wall?

This is for a live room.

You can see the details on this thread:

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=3961

Thanks in advance!

Rodrigo

[knightfly]

Rodrigo, can you give actual dimensions (and your reasoning) for that long slat wall? Need board thickness, width, slot widths, depth from rear of the slats to the wall, what you're putting inside and WHERE, and WHY - thanks... Steve

[igloo]

Knightfly, thanks for your reply.

The reasoning for this is to prevent the build up of standing waves. All my walls are parallel walls; so I read about this slat wall in the SAE site, and thought it would be a good idea that is practical without loosing too much space.

My studio room is 2.62 m x 3.10 m with a sloped ceiling that goes from 4.00 m to 3.60 m. The longest wall (3.10 m) opposite to the entrance is the one I want to treat.

Since it's 2.62 from the front wall with the entrance I figured the problematic frequencies would be:
Fundamental: 65.45 Hz
1st Harmonic: 130.91 Hz
2nd Harmonic: 196.37 Hz
3rd Harmonic: 261.83 Hz

If I build a Helmholtz resonator wall I would use the following dimensions:

Slot width. 5 mm
Slat width. 100 mm
Depth from wall. 200 mm (average of 100mm and 300mm)
Slat Depth. 25 mm
Effective depth of slot 30 mm

Absorption frequency 261 Hz

So it would be a slat wall angled from 10 cm at floor level to 30 cm at ceiling level.

My ceiling is filled with hangers. Is this slat wall a good idea? should I use only corner absorbers? If I do build this slat wall, is there a need for corner absorbers? Any help is very appreciated!

thanks,

Rodrigo

[igloo]

I missed one of your questions. I was thinking of placing 2" thick 703 inside the slat wall. With the insulation just behind the slats and sloped as the whole wall system.

My main goal is to have a balanced tracking room. My problem is that I can't give up much space in the room. I know Ethan's panel traps are efficient and don't take a lot of space. But they have specific frequencies, and I thought I need a broadband absorption solution. What do you think?

[knightfly]

Looking at your dimensions I see quite a bit of activity around the 261 hZ frequency, and you will need SOMETHING on that wall to kill flutter; however, you've apparently used the erroneous helmholtz calculator from the SAE site, which (like virtually ALL the helmholtz calculators on the web) are WRONG - this stems back from an apparently incorrect formula published originally in the Audio Engineer's Handbook, since spread all over the web. The corrected version of the spreadsheet you used is located in our Acoustics forum, and for your dimensions it returns a center frequency of 155 hZ, not 261.

I think your plan to combat parallelism in that wall makes as much sense as anything; a slat wall won't suck all the highs out of the room, but it will provide some diffusion and the angle, while not even 6 degrees, will help with flutter (as will the slats themselves, just a little) -

If you leave all your slat/slot/depth, etc, the same but widen the SLOT width to 16mm, it will not only give you the actual frequency you wanted but will also improve the diffusion aspect a bit. Alternately, if you keep the slot width at 5mm you could gain a bit of floor space by lowering the average depth to 70mm.

However, that brings up another consideration; if you build a resonator with average depth of only 70mm, then the total depth would be only twice that or 140mm. For a 3.6m high wall, to get a 6 degree angle you need a 1:10 ratio, so the total depth of a resonator that tall should be more like .36m, or 360mm.

You could get the target frequency with a combination of 5mm slot, 65mm slat, 180mm average depth, and thinner slats of 15mm - this would keep the narrower slot width.

There are a couple of problems with this approach that I see; one, if you tilt this slat wall enough to also help with flutter, the room will have a feeling of "falling in on top of you" since the top of the wall will be nearly 14" out of plumb - and two, I'm not sure you're going to want (or need) that much trapping in this particular band; according to a Bonello distribution, you don't even HAVE a problem there. All it shows is a slight LACK of modes around 60 hZ, but overall not a bad choice of dimensions at all.

You already have a LOT of trapping built into your ceiling, which is good; and the corner absorbers you plan are going to help with broadband absorption even more. I personally would look more at building some PORTABLE treatments that you can move around on that wall as necessary; something like 4" rigid fiberglass or rockwool, backed with plywood, approximately 1 meter wide (or a full width of plywood) by at least 2 meters tall, with stabilizers on the bottom so they will stand on their own; these could then be placed in a zig-zag pattern along the wall to handle the flutter problems from parallelism; the other advantage is, you could REVERSE them (or some of them) to taste to control how bright the room is (plywood out = bright, absorbent out = not-so-bright :=)

Acoustics are hard enough to predict without building everything PERMANENT; this would give some flexibility to experiment til you get the room sounding like you want... Steve

[igloo]

knightfly, thanks for your reply!

It definitely makes sense. And being my only recording room, I need versatility. So I was thinking about the hinged panel absorbers at the SAE site instead of portable panels. I'll still be able to put them on a zig zag pattern, and have a permanent solution that allows me to quickly change the acoustics on my room... I think that's the road I'm headed at...


thanks for sharing all your experience and knowledge in acoustics!

cheers,

Rodrigo