Trying to treat an awkwardly small room

Hi all, I'd firstly like to thank this site and it's contributors again! It's been such a great resource, and I'm now getting my teeth into another project, this time at the FE college I work at. We moved to a brand new building in september, and although we now have some great recording equipment, we have a terrible control room, because it is a strange shape, small and has an unnecessary window (and sounds dreadful!). The isolation between rooms is pretty bad (especially with two bad metal bands rehearsing either side of you!) and the air-con is SOOO loud, so I'm not looking to perform miracles here, just make the best of what we've got. I have to convince the head of music, my line manager, and the the deputy principle that this a worthwhile cause before I get any money to carry out the works, so I want it to be right. I've added up all of the materials for what I have already planned, and it's going to be around £1000. This covers timber for the frames, the high density fibreglass from Wickes, and the fabric from Custom Audio Designs. I plan to build the traps using the method outlined in Rod's book p.172-4, which I have built before, and turned out great. Like the ones I built, each will measure 1230 x 630 x 70mm (frames included), excluding one or two that need to be a bit smaller, and of course the large rear trap, which in total will measure 3400 x 930 x 120mm, with an air gap of 220mm behind. The cloud I am slightly unsure about, but after some research here, it looks like a hard-top construction, roughly 1200 x 2400 x 300mm, filled with fluffy insulation. The room dimensions are 3400(h) x 3630(w) x 4500 (d)mm at the widest and deepest points. The walls each side of the desk (left and right) are painted breezeblock, the rest of the walls are plasterboard (clearly not enough layers), and the ceiling is false 30mm "acoustic tile". (We've been had!) The window in front of the desk looks out onto the small live room, the one to the left of the desk looks onto a general classroom/rehearsal space, and the one to the rear looks into the vocal booth. The window looking into the classroom is a bit pointless, although is does let in some natural light, which is nice. However, we plan to cover this window with some heavy curtain we have stored from the old build to help with imaging. After a bit of sine-wave sweeping, it became very apparent that there are loads of peaks and nulls, so I want to control this as much as possible with bass traps, and I also wondered about hanging a cloud over the mix position- a good idea? So I guess my first question is, do my improvements look adequate, and how about that cloud? (OK, two questions) Cheers, Ross

Ross Peters wrote:

do my improvements look adequate

No, you need more bass trapping if possible. The wall-ceiling corners are a great place to add more straddling bass traps. Especially at the top of the front and rear walls, but the side wall tops are good too. --Ethan

Hi Ethan, Thanks for your input, I agree. I should have expanded on the ceiling issue a bit more- as it is false, and there is an 8 foot air gap above, I think it will be difficult to add traps straddling the wall/ceiling, as I won't be able to fix anything directly to the ceiling. Unless I make some sort of bracket.... I think there maybe room for two more at the front and two on the sides, I'll have to draw it up. I also have to be sure I don't spend too much theoretical dosh! Any thoughts on the cloud? Cheers, Ross

Ross Peters wrote:

it is false, and there is an 8 foot air gap above

Is this a drop ceiling grid? In that case I'd lay 12-inch thick batts of fluffy fiberglass over the ceiling tiles.

Any thoughts on the cloud?

Rather than hang a cloud, I'd simply replace the tiles at those locations with rigid fiberglass one to two inches thick. --Ethan

Thanks Ethan, It is a drop ceiling grid, but unfortunately, I don't think I'll be allowed to install fibreglass above the ceiling tiles- college internal politics! There is a lot of red tape, so it is easier for me to impact upon what is already here as little as possible. When we first moved to this new site, there were lots of people moaning about how bad the sound isolation was between rooms in the music department. This led to a small victory, where the builders eventually came back to add a foam-lead sheet-foam sandwich layer above the ceiling tiles, which didn't seem to make a great impact to isolation, but may have contributed to what you are suggesting with the 12" thick batts of fluffy fibreglass- not sure though. Similarly, with your suggestion of replacing the tiles with rigid fibreglass, I would rather take the easy route and add to what is already here, rather than replacing. Incidently, the acoustic tiles are comprised of 20mm rigid fibreglass, backed with 10mm plasterboard and 5mm open-cell foam- so this is quite close to what you have suggested. I don't know how absorbsive these are, so I wondered if adding a cloud and angling it toward the back of the room would be more effective at reducing flutter above the mix position. Here is a drawing of the extra bass traps you suggested I need, minus the cloud. Cheers, Ross.

After much effort, it looks like the college will agree to fund acoustic treatment for the control room, so I have been working on a plan to treat the live room too! Here is our live room, with the treatment I have come up with so far. It's mainly used as a practice room, but it is our main live room, and sounds horrible at the moment. I've done some sine wave sweeping, and its lowest mode is around 36Hz, which will hopefully be tamed with the corner traps, and some more of the low frequency absorption coming from the polys, as I intend to fill the cavities with fibreglass. I'm also considering hanging a heavy curtain over the window next to the door, to counter flutter echoes. This really is a bit of a stab in the dark with regards to placement and amount of diffusion and absorption. I know I need to work out the RT60 by calculating the absorption coefficients, and other math stuff that hurts my brain, but I thought I'd try to get the ball moving. Any thoughts or comments would be very much welcomed! I have already made one of the shallow polys, and one of the skylines (which weighs a ton!). I have also made some of the perforated panels backed with 2" Auralex foam we have laying around. I think they look pretty cool, but will they sound cool? I should probably followed a design, rather than taking influences from all over the place and coming up with my own...... I'm hoping they will provide diffusion and some absorption, the main broadband absorption coming from the corner traps To keep costs low, I have disassembled an old wooden classroom cupboard, which had a nice finish to it. These panels were made from the shelves. The back of the cupboard was made from 9mm ply, which I thought I could use to make a poly. However, without looking into the design and construction a great deal before, I fear I may have not made it high enough (ie. tight enough arc). It was very difficult to bend, so I bent it as much as I could. Below is a picture of it. I've since bought F Alton Everest & Ken C Pohlmann's 'Master Handbook Of Acoustics', as I keep seeing it mentioned- what a great book! The poly construction he describes (p.207) indicates that they have a much bigger height to chord length ratio than mine. Will this be a problem? Presumably it will provide less diffusion? Hopefully someone here will be able to shed some light on my dull brain! Thanks for reading, Ross

i think the treatments near the ceiling-wall corners would be better suited for bass trapping (like in your g44 drawing) and the angled bits and other treatments lower into the space to add diffusion and scattering. you could build some slot resonators and/or polys for the wall-ceiling corners, panels (like in g44) or just super chunk it and add some slats for add some reflection.

Thanks for the thoughts Gullfo. I've been thinking more about slot resonators for this room recently, and perhaps for the control room as well. From what I can see from various threads, it looks like a very popular choice for maintaining the liveliness of the room- not to mention how great they look. I'd also forgotten about treating the ceiling-wall corners-der! So thanks for the reminder. I'll start re-drawing tomorrow. Do you think building slot resonators in the wall-wall corners would be better than the traps I've proposed here? Would I tune them to the lowest modal frequency? Cheers, Ross

the device i drew is not really a slat resonator. it's a super chunk trap like what (i presume) you drew but it has some slats spaced over it to add some reflections back into the room so you don't end up totally dead... you could leave the ends in the tri-corners purely absorptive and put the hard bits around the middle to reflect back at about ear level. of course you could also put in proper slat units in the middle sections which provide wide band absorption with good high frequency reinforcement. edit: another option is to put in a false ceiling (stretched cloth) about 2' down and put in hangers. this would also give you a place to put recessed lights, ducting, wiring, etc. you could then face the cloth with some polys. see additional attached.

Wow, thanks for the ideas Gullfo, I really appreciate your time. The corner traps I've drawn are not super chunks, but 60mm rigid fibreglass panels in a wooden frame, wrapped in fabric. I intended the space behind the traps to be filled with low density fibreglass. I think super chunks may be better, but I'm looking to be as cost effective as possible. I like the idea of leaving the tri-corners purely absorbsive like you've suggested. I wish I could, but unfortunately, I won't be able to do the dropped ceiling idea as you suggested. I'm not really sure if I've made it clear, but this is a college building that has been in use for the past year, so all ducting, lighting etc has already been completed- in that lovely, mood provoking, white-walled, strip light style! Anything on the ceiling, I think will be a definate no no. Shame... Anywho, I've come up with a new idea for the live room, prior to your post, so here are some drawings to illustrate my thoughts so far. I can't put any diffusors on the bare wall opposite the control room window (ie. not the one with the polys) because the wooden rail holds guitar and cable hangers. And again, I intend to put low density fibreglass in the cavities behind each trap. Please ignore the tri-corner intersections where the traps continue through each other- I haven't worked out how to use Sketchup to erase the bits I don't need yet, but I think you can get the idea. Cheers, Ross