Mix room, Chicago, IL

Hi everybody! I'm putting together a mix room in my house in Chicago, IL. I posted about this room a while ago. I got the following drawings from Ready Acoustics as a suggested setup (they offer a low cost service fr this purpose), and wanted to get a second opinion. I'm unable to do construction in this room, as it's in a rental house, so I'm limited to what treatment can be done. I've currently got 8 bass traps made from Johns Manville 814 (3.0 PCF; equivalent to OC703) and 9 HF panels of JM 817 (6.0 PCF; equivalent to OC705). The Bass Traps are constructed with three sheets (6" total) of 814 with a small wood frame behind the panels and burlap covering. The HF panels are 1 sheet (2") of 817 with a small wood frame behind the panels and burlap covering. I've already put superchunks in the corners as indicated in the drawing. I'd like to know if you all think this is a good way to go about setting this room up, or if you have other suggestions. In case it's not evident from the drawings, the proposed listening position is 66% off the wall behind the speakers. (33% off the wall behind the listening position). I do realize that standard procedure is to set the room up with speakers firing down the long dimension of the room. When I mentioned this, Joel at ready acoustics indicated that this arrangement would be better because it would be more symmetrical. He also indicated that treatment behind the listening position probably wouldn't be necessary because of the narrow strip of wall that would produce specular reflections to the listening position. In the drawing, the red panels are 6" bass traps, the white panels are 6" bass traps that are "optional for this location", the blue panels are 2" HF panels. The corners are filled with superchunks (34" face, made of JM814). Any information or opinions are sincerely appreciated! Thanks much! Mike Taylor

i think you're missing some absorption on the small angled wall leading into the cubby hole.

Agreed. Actually, I would recommend 'filling' that cubby with absorption. Also, you should check side wall reflection points. Use a mirror. With all that absorption in the room, the decay will be very fast at mid and high frequencies & I would recommend using slats across the front corner traps and anywhere the slats will not cause reflections into the RFZ. Cheers, John

Thanks for the replys, guys. I'm definitely going to put some sort of absorption into the alcove. (probably a 6" trap with a 4" air gap). I really want to use it as a place to put my soldering and workbench. I'll cover the opening with a curtain to get it out of the way. Regarding the slats for the corner traps: I've heard of guys using FRK or even thin-ish cardboard in front of something like to that make the room less dead. Is that something you'd recommend? Also, given the listening position, I've been told I could leave the 3 traps indicated in white out. How do you feel about that suggestion? I assume that would help immensely with the M/H decay time. Thanks again, Mike

Yes, the panels behind the speakers aren't necessary if the room is getting too 'dead'. Cheers, John

Thanks, John! I'm going to have to look into the whole "slats" thing. I'm not sure how to make that happen in terms of the build. I'm going to put a 3'9" wide, 6" deep, 4' tall trap in the alcove. That will leave an air gap of about 2' 1 1/8" behind it. Is that too large an air gap? I've decided I won't use the alcove for my soldering. It will leave me about 1'4" between the front of the trap and the front of the alcove... I think I'll put a shelf in there so I can hold mics and such. I still intend to cover the opening with a curtain. (Unless you think that's not necessary). I've included another drawing. Does this look like the right idea? Is it really necessary to backfill with fluffy stuff behind that trap? Thanks again! Mike

maybe put a few rolls of pink insulation in behind the rigid insulation panels.

Thanks, Glenn. (again, sorry I didn't mention that previously!) I think I'll do that. Regarding the slat covers for the corner traps (behind the speakers): Everything I can find that talks about slat traps is talking about helmholz resonators. My understanding is that this requires sealed compartments, etc. In my room, these corner traps are literally wedges of JM 814 stacked in the corner. Nothing is sealed. My question is: If I put slats in front of the corner traps, will they still perform as expected for low frequencies? Does it matter that they aren't sealed corners? Does the spacing of the slats matter in this instance? (because I'm not building a helmholz resonator) I have the formula for spacing for a helmholz resonator from Rod's book (f=2160*sqrt(r/((d*D)*(r+w))), but again this seems to target a specific frequency, rather than the broadband low end absorption I want. Thanks again guys. This is really helpful.

for proper Helmholtz action, the air cavity has to be sealed. there are several options, one is put some widely spaced slats to improve high frequency reflections off the absorber with little impact to its low frequency absorption. you could decide to build a proper slot resonator but your absorber response will be completely different than your current design. this is due the the range that a slot resonator will work over versus the cloth covered insulation. the formula you show is used to define a targeted frequency range. to create a more broadband effect, the changing depth cavity and some alteration to slat wide and slot opening will create a slightly wider range, and adding cloth behind the slats will flatten the Q of the absorber and reduce its efficiency. you could simply put some widely space slats over the middle section of the corner absorber to add some reflections and leave the top and bottom (effectively the tricorners) as plain absorber.

Thanks, Glenn. I assumed as much regarding the formula, I just wasn't sure what you were getting at with "widely spaced slats". Is something like this what you're talking about? (the slats are 1x4's). It seems that with that kind of spacing, there would be questionable benefit at mid/high frequencies in terms of keeping the room alive. Maybe I'm wrong, though. Thanks, Mike

that's the idea although you can use smaller ones spaced a little closer as well. you could also put a poly over the middle if you needed more reflection. you could also put a slat panel or angled slat panels like you see in a number of John's designs.

slat panels

Glenn, Thanks much for the information. I think I'm going to put a QRD over the middle of those traps. Seems like it wouldn't be a problem in terms of early reflections, and it would help in terms of liveliness. Thanks for all your help! Mike