Layout and treatment in unusual room

Dear all, First post! I have perused this site recently to improve my general knowledge about acoustics treatment, but now I really need your help! Any input is much appreciated. BACKGROUND: I moved from Sweden to Bergen/Norway this week. I produce club music (house) on the side from my regular job and need a space to write, mix and sometimes track vocals or DI bass/guitar. I monitor at moderate volume. I rented a flat on the 2nd floor (3 story building) based on pictures (wide-eye lense). The space to the left now labeled "Office" turned out to be a small and nearly perfect cube and so not suitable. The largest room however, has an intriguing shape that instantly reminded me of John's control room drawings ;). See my drawing. SPACE: Ceiling: 2,46m Floor: wood with hard finish Windows: 15cm depth from inner wall. Walls: 0,12m thick behind sofa, 16cm behind record cabinet, 24cm for outer walls. They appear to be gypsum->insulation->wood panel for outer walls, and perhaps gypsum/gypsum for inner walls. The upper left corner faces a 4m corridor, no door. !I just noticed I got the angle given (54 degrees) in the mix position wrong.. I'll try to fix that later today.. RESTRICTIONS: *Choosing this room means it also has to function as a living/entertaining room. *I want to make the least possible damage to walls, ceiling and floor. Any damages will be charged when I move within 3 years. * I need to set this up with a minimum of delay and work, as I need to finish some ongoing projects. I have 2 weeks before commencing a new and demanding position at work. FIRST IMPRESSIONS: With the placement drawn in and temporary absorption behind and on the sides of the monitors (thin foam, mostly high freq abs), the stereo image immediately felt great in the mix position. But the frequency response is all wrong. My first though was "where has all the bass gone?". A quick check playing a series of tones from 60Hz-200Hz and subjectively judging the perceived volume revealed, for example: 85-90Hz. ---- (nearly lost) 90-99Hz -- 105-109Hz -- 110-115 ok 116-126 ++ 127-129 +++ 130-135 +++ 136-139 ++++ 140-147 ++ 148-155 ok 155-159 -- I realize this is not very precise, but quickly confirmed that there is indeed a problem. I could try to do a more accurate measurement, but I haven't got the proper equipment.. QUESTIONS: 1. Is this the best placement in this room, or should I go against one of the walls instead? Going against the wall facing the "office" would allow me to put the computer behind that wall = less noise when tracking vocals (although this is not a significant problem even when untreated, and can also be countered with a moveable absorber). 2. Would a floor-to-ceiling bass/broadband trap build by stacking rigid mineral wool (covered with a drop-down cloth) behind the monitors help enough to counter the nodes in the room? 3. What if I add a broadband absorber (http://www.johnlsayers.com/HR/index1.htm) in the opposite corner beside the sofa? 4. I'd rather not do *any* ceiling treatment considering the damage I would do to the walls to mount it, but if necessary I could perhaps put something in the first reflection point monitors/mixpos.. 5. Any other thoughts and suggestions you might have. BUDGET: Around $1000-$2000 but I'd love it if it was lower, having just moved countries with many things to replace, two people to feed and one salary.. Warm regards and thanks in advance. I will monitor this thread closely.. - David

Hi, I'm not an expert in accoustic... yet ;) Just noticed your "sound measurements" and have an advice. You could get all types of measurements (and much more objective) by using demo of ETF software. http://www.etfacoustic.com/download.html Make sure you connect everything as described in help file to give some results. Best regards, Tomas

Tomas wrote:

Hi, Just noticed your "sound measurements" and have an advice. You could get all types of measurements (and much more objective) by using demo of ETF software. http://www.etfacoustic.com/download.html Make sure you connect everything as described in help file to give some results.

Hi Tomas, Thanks for the advice. ATM I have only got a hypercardoid mic (Røde NT3) which is probably not ideal for these measurements..? Is there any reliable way forward without performing this test? What do you all think.. - david

This is to give somthing to read until you get response from someone who knows what they talk about. Some of MY THOUGHTS (could be wrong). I started my own room analyelysis with cardioid and data collected was definitelly useful. Proximity effect is smooth curve, and modes have quite big variations in relativelly small frequency range. I hope hypercardoid should "see" problems as well, but there is risk of phase reversal from back of the microphoe to cause problems in LF. Anyway I bought digital SPL meter that has output from it's omni mic, for ~100$. In your budget it's not major expense, and it should prove useful in the future. Treating room with measurements is whole lot more fun. Because some changes in trap placement are to subtle to judge by ear (mine at least), but obvious on ETF.

The Radio Shack SPL meter combines a microphone and a preamp (line level) that can be used to drive the input of a sound card at the line input (not the mic input). This is a perfectly good choice for a microphone to tune low frequency acoustics and see room reflections at higher frequencies. If this is the intended purpose of the software, then the low cost RS meter is all that should be used. A calibration file link for this unit resides on our site on the support page. This file makes the microphone roughly accurate to a dB up to about 5 KHz.

Another thing, I've read somewhere in these or other forums that you need at least 30% of are treated to have some effect, preferably more that 50%. And indeed I can confirm that single or two corner treatment has some positive effect, after which you get addicted to treating your room. (check my thread http://www.johnlsayers.com/phpBB2/viewtopic.php?t=4038 to see how crazy are my plans). I have similar requirements as you - don't want to ruin the place completely, and take treatment with me when I move. The chunks I make for ceiling/wall corner will be held by 2 screws at ceiling/wall junction each. The rest is free-standing stuff. Moving away, hopefully, I will unscrew these screws and caulk the holes unnoticeable. Ahh.. almost forgot, there will be two "flat" traps on the ceiling - some more holes. But unless you have really exotic ceiling fixing holes should be no big issue compared to building all the treatment initially. Hope that helps, Tomas

Hi, Yes the trap you plan would help. I would make the other trap behind you as big as possible and you need a wallpanel near the door to kill reflections. Tha kight stripes are cornerabsorber in the wall/ceiling corners. You my not need it to make all way round, but you can add and listen and add and listen until it sounds fine. Maybe you buy an inexpensive Behringer ECM8000 and then you can measure your room with ETF, most people here do it this way. Afterwards you could build resonators or paneltraps if needed. Florian

Great feedback guys!

Tomas wrote:

you need at least 30% of are treated to have some effect, preferably more that 50%... a single or two corner treatment has some positive effect

the thing is.. in this room.. it has to look ok while everything is in there, and look as much like "normal wear and tear" as possible when I take it down again.. the place is really spotless now. given that, treating 30-50% is probably not doable. so I want to do the most efficient solution possible with corner absorbers and absorption around the mixing position. but..

Tomas wrote:

I have similar requirements as you - don't want to ruin the place completely, and take treatment with me when I move. The chunks I make for ceiling/wall corner will be held by 2 screws at ceiling/wall junction each. The rest is free-standing stuff. Moving away, hopefully, I will unscrew these screws and caulk the holes unnoticeable. Ahh.. almost forgot, there will be two "flat" traps on the ceiling - some more holes. But unless you have really exotic ceiling fixing holes should be no big issue compared to building all the treatment initially.

got any construction-plans for those only-2-screws-chunks? I'm worried they'll fall down (and take the wall with them?) since these walls are just thin gypsum..

the dreamer wrote:

Yes the trap you plan would help. I would make the other trap behind you as big as possible and you need a wallpanel near the door to kill reflections.

cool. maybe a "superchunk" in each corner would be easiest. and ahh yes, the back wall! how could I forget. I will have to talk my gf out of that corner, she had a nice lamp in mind ...

Tha kight stripes are cornerabsorber in the wall/ceiling corners. You my not need it to make all way round, but you can add and listen and add and listen until it sounds fine.

what kind of corner absorbers? anything that's light, looks good and does not destroy walls when taken down?

Maybe you buy an inexpensive Behringer ECM8000 and then you can measure your room with ETF, most people here do it this way. Afterwards you could build resonators or paneltraps if needed.

Good suggestion! I'll order one of these. Before I order up the material (Rockwool most probably), I'll let this sit for a while in case anyone else wants to chime in.. So I take it the room layout is definitely ok then.... ? I'll play around with monitor placement a bit tonight..

You could do the wall/ceiling corner absorbers like this: http://www.bobgolds.com/TrapMartin/home.htm So 4 screws per Absorber want hurt too much I suppose. or you make them like the superchunks for more effect. Florian

el davo wrote:

Great feedback guys! got any construction-plans for those only-2-screws-chunks? I'm worried they'll fall down (and take the wall with them?) since these walls are just thin gypsum..

Well, I'd not put it on 2 screws in gypsum. It's meant for concrete walls. The design is in my topic. Basically it has long bolts running through all length and extending ouside the chunk. These can be used to hang it to the corner. I intend to use put one hook to ceil/wall corner for each side of the chunk, to split 30kg load in 2. Then attach the bolt end to hook using steel wire. I have 3 bolts in each chunk so all of them can be used for support, I'm no expert in construction, so can't suggest how to place it safely in gypsum. I've been consulted for specific hooks for concrete walls, and they said they can hold much more.

el davo wrote:

cool. maybe a "superchunk" in each corner would be easiest. and ahh yes, the back wall! how could I forget. I will have to talk my gf out of that corner, she had a nice lamp in mind ...

Start the construction, and you will beg her to return back home ;)

what kind of corner absorbers? anything that's light, looks good and does not destroy walls when taken down?

to my information, you don't want "light", because it won't absorb lows. You have to see how heavy can you make in your current situation. 3pcf density is recommended for acoustic treatment. And the thicker it is the wider the Q of absorbtion. Actually even a single sheet of 4" rock would make the difference. And I've seen in some forums how it can be attached using just 2 screws in the corner. Something like attached in my picture. They use springs instead of regular cable. Also built like florian suggested can be hung this way. But you should really calculate the costs of repairing the holes in walls, to see if it's really worth compromising sound quality for 3 years instead of maybe some 100$ to fix later. I believe it's more mental than real problem.