[cinepro]

My company has recently relocated to a new building, and has converted 6 offices into listening rooms for 5.1 and 6.1 soundtracks. Now that I've set up the equipment, I'm starting to experiment with acoustical treatments.  I've been reading past posts on this forum, and am looking forward to improving the sound.

Here are the measurements for the different rooms.  All have 8' ceilings.

1. 10'x11'
2. 10.5'x10'
3. 10.5'x10'
4. 15.5'x16'
5. 10'x16'
6. 9'x16'

Each room has a monitor/desk setup where the listener will be sitting at a large desk with the display and front monitors on shelf at eye level, approximately 3' from the back wall.  The floors are all padded industrial carpet, the walls are drywall, and the ceilings are acoustic drop ceiling with 12-24" of insulation above (the previous owner's attempt to keep out extraneous noise from a nearby airport, and insulate the rooms from the warm summers).

I have a bunch of acoustical foam left over from another facility, and an Auralex Roominator kit.  I'd like the 15.5'x16' room to be the nicest, so I'll be investing in some GIK or similar panels.  The others can be foam or fabric panels.

For the smaller rooms (#1,2&3), I'll probably try to use the foam I have.  IT is mostly 1" 2'x4' charcoal gray, as well as some 2'x4' "sawtooth" foam.  I plan to cover the first-reflection points (sides and ceiling) with 2" of foam, with 60-70% coverage of the rest of the walls in 1" foam.  I have some irregular foam scraps that I was going to form into 1'x1'x1' cubes and put them in the four front corners to see if this would help with any bass irregularities. 

I used ETF years ago in setting up my home theater, so I plan on bringing my laptop in to take some measurements.  But with such small rooms, I'm not hoping for great things. 

I obviously don't have a huge budget, and I'd like to spend most of my $$$ on the one larger room, so I'm wondering if there are good ideas for how to most effectively use what I have, and get the most bang for my buck from the money I do have.

[bpape]

Sounds like a fun project.

IMO, the 10x16 room has the best chance at the best sound.  The 15.5x16x8 room is almost a perfect cube.

Smaller rooms require proportionately more bass control to get things cleaned up.  Square or cubic rooms also require proportionately more.  Rooms 1-3 are almost square.  Room 4 is almost a perfect cube.  Concentrating in those with primarily 1" foam is going to do little to nothing to help the overall situaion - might make it worse by overdoing the HF absorbtion and leaving the problem areas untouched.

None of the rooms should have 60-70% of their surface covered in primarily thin materials, much less foam.  All of the rooms need some sort of bottom end control and unfortunately, a 1' foam cube in 4 corners isn't enought.  It's better than nothing, but realistically not much.

If it was me, I'd concentrate on doing the 9.5x16 and the 10x16 rooms right with broadband bass control in the corners, a dead front wall, and appropriate refleciton treatments on the side walls.  Additional decay control can be added later.  The foam is fine for now on the front and side walls to save budget.

For the other rooms:
Use the foam that you have on the side walls for reflections.  Use the thicker material on the front wall since the rooms are so small and I'm quite sure SBIR will become an issue.  Purchase some REAL absorbers such as a DIY 4" from OC703, our 244 panel, etc.  Use these to straddle the front corners at this time.  Use the foam cubes in the upper rear tri corners for now until budget allows something better.

The key to all of this is balance.  Little to no bass control and too much thin HF only absorbtion may sound better when you clap or snap your fingers, but with music and HT, the imbalance will be severe.

If you have sketches of the rooms, shoot them to me - I'd be happy to take a look and make some more specific recommendations.

Bryan

[8thnerve]

Focus on the corners.  If you are on a budget get some rock wool.  It's cheap and almost as good as rigid fiberglass.  Cut it to fit in the corners, give it at least 6 inches, but ideally just put a one foot by one foot tower in the corner to the ceiling.  Then put a reflective panel on the front of it.  A thin panel of MDF, plastic, laminate, whatever, but try to pick something that is not resonant.  Make sure it covers the entire front of the absorptive material with about a half inch to one inch gap from the wall to the edge of the reflective panel.  That's about as cheap as you can get.

Of course, some triangular pieces and horizontal corner products will help tremendously as well, especially in small rooms.

[weirdo]

along the same lines, I am searching for triangular shaped acoustic treatment, approximately 5 inches across and about 3 feet long.
Advice appreciated.

[bpape]

With all due respect, I would not cover the absorbtion in a multi-channel room like that.  Target decay times are lower in a multi-channel environment.  If you want to reduce the HF absorbtion in the rear absorbers, use something like a 10-20 mil plastic stretched tight or just use an FSK facing.

Corners are great for broadband but the front wall also needs to be dead to keep the rear surround channels from reflecting off the front wall and messing up the front soundstage.  This is very different than in a 2 channel room.

Bryan

[8thnerve]

With all due respect, I would not cover the absorbtion in a multi-channel room like that.  Target decay times are lower in a multi-channel environment.  If you want to reduce the HF absorbtion in the rear absorbers, use something like a 10-20 mil plastic stretched tight or just use an FSK facing.

Corners are great for broadband but the front wall also needs to be dead to keep the rear surround channels from reflecting off the front wall and messing up the front soundstage.  This is very different than in a 2 channel room.

Bryan

And I respectfully disagree.  In that small room, it is very easy to completely kill all the high frequency energy.  An FSK would certainly be better than plastic, and much better than nothing at all, but a better reflective layer will yield a more linear frequency response.  You can achieve a very low decay time with no exposed absorption with proper treatment.

It's certainly a unique opportunity to try two different approaches and compare the results!

Best Regards,

Nathan Loyer
Eighth Nerve

[bpape]

Agreed.  FSK is better than the plastic and more broadband.  Yes - we don't want to kill the high end too much - hence my comments about not doing too much 1" foam and ignoring the rest.

FYI, here are the recommended decay time spreads for a 10x10x8 room (courtesy Bob Golds):

RT60 (IEC/AEC N 12-A standard): 187 ms
-  ±50ms from 200Hz to 3.5kHz = 137 to 237ms
-  ±100ms above 3.5kHz = 87 to 287ms
-  <+300ms at 63hz = 487ms
-  300<RT60<600ms

RT60 (ITU/EBU Control Room Recommended): 158 ms
-  ±50ms from 200Hz to 4kHz = 108 to 208ms
-  <+300ms at 63hz = 458ms
-  200<RT60<400ms
Absorbtion to achieve ITU RT60: 278 sabins

(sabins - front wall - carpet) / Left+Right+Rear wall: 32 %
(sabins - front wall) / Left+Right+Rear wall: 69 %
Schroeder Fc: 149hz
 - Room Modes dominate: 56hz to 149hz
 - Diffraction and Diffusion dominate: 149hz to 596hz
 - Specular reflections and ray accoustics prevail: 596hz to 20000hz

Untreated room that size with 1 chair and 1 person assuming single drywall, 5/16" carpet and no treatments:

RT60   0.30   0.64   0.70   0.63   0.46   0.49

Killing front wall with 2" mineral wool, 2 2'x4' foam absorbers for reflections on sides, and small (1' wide x 4" thick) absorbant FSK faced absorbers in rear corners floor to ceiling

RT60   0.30   0.34   0.29   0.30   0.29   0.30

Still well more lively than recommendations as it should be since a multi-channel listening room should be approx 20-25% more lively than a control room in most cases.  A nice smooth balance of control throughout the range, reflections dealt with, upper bass/lower mid boom dealt with, front wall surround reflections killed, etc.

Different strokes... 

Bryan