While thinking about finally tidying up my attic room, I've come across acoustic room treatment again. Been thinking about that a while back already, but never managed to try it out actually. Here's my probably somewhat unusual idea (haven't seen that done before anywhere), so please tell me what you think.
As you can see on the picture below, my room has slanted walls from top to bottom. I'm planning to generate some out-of-sight storage space by adding sliding doors to both lower sides, probably up to the height of the window sill. That will leave me with ~2m high OSB walls from above the window sill up to the top.
What about batten down those walls, put some 10cm thick rigid fiberglass in between, and then cover up that whole construction with fabric? I would basically hide the whole wall behind a huge absorber, instead of hanging individual absorbers to the wall.
Judging by a number of websites and forum posts, there're lots and lots of different approaches to treating a room and every single person seems to have its one-and-only way to go, so I'm basically hoping for some opinions whether this might work or is simply a stupid idea. In the end I'll have to try it for myself anyhow, I guess...
As you can see on the picture below, my room has slanted walls from top to bottom. I'm planning to generate some out-of-sight storage space by adding sliding doors to both lower sides, probably up to the height of the window sill. That will leave me with ~2m high OSB walls from above the window sill up to the top.
What about batten down those walls, put some 10cm thick rigid fiberglass in between, and then cover up that whole construction with fabric? I would basically hide the whole wall behind a huge absorber, instead of hanging individual absorbers to the wall.
Judging by a number of websites and forum posts, there're lots and lots of different approaches to treating a room and every single person seems to have its one-and-only way to go, so I'm basically hoping for some opinions whether this might work or is simply a stupid idea. In the end I'll have to try it for myself anyhow, I guess...
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As it is an attic I wouldn't worry much about any room modes as they will be absent in environment free from rigid, heavy, perpendicular boundaries. What is more, an insulation layer under OSB already acts as very high performance, broad-band absorber. In order not to over-damp mid and high frequency decays I would't put any absorbing material on the surfaces of this room. Slanted walls will avoid straght-to-listener reflections and it will diffuse soundfield nicely using secondary reflections from the floor. One restriction is that heavy bass damping already buried under OSB will require powerful bass response from your playback systems. If not, the bass response will be simply too lean. An active system with capable subwoofers (capable of large displecement volume at low distortion) and properly implemented equalization will work best.
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Hi Cal, I'm not sure if I got you right and what kind of drawing you mean, but the attic is basically sealed air-tight like the rest of the house, and a ventilation system with heat recovery is on duty.
I've noticed that already. Listening to The Prodigy is no fun at all... But I'm fine with the lower end - for the moment, at least.
I'm not totally satisfied with overall sound quality though. I'm still moving around the speakers to find a good position, but there're huuuuge differences.
I'm afraid that those slanted walls are going to be a pretty severe problem, speaking from experience. Here is a picture of one guy's room after he finally tamed the room modes and the imaging-destroying reflections:
A link to the thread where the realities of such a room shape became understood: Acoustical help with Room EQ Wizard and in room response and decay time - Technical/Modifications - The Klipsch Audio Community
A link to the thread where the realities of such a room shape became understood: Acoustical help with Room EQ Wizard and in room response and decay time - Technical/Modifications - The Klipsch Audio Community
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A link to the final acoustic measurements and resultant acoustic treatments in that room: Active Bi-Amping/Tri-Amping FAQ - Page 5 - Technical/Modifications - The Klipsch Audio Community
Cal is a roof inspector.
Ventilation is for heat/moisture buildup in different seasons that can cause mold and/or roof failure.
How to Insulate an Attic
Hi Lasse,
It's my understanding that both absorbtion and diffusion are required for good sound reproduction. I'm right in the process of doing the same as you are in my house and have adopted for a live end dead end (LEDE) approach as briefly described in this link;
What is "LEDE - Live End, Dead End - inSync"? | Sweetwater
I'm also constructing the diffusors as detailed in this link;
Depot Diffuser construction
Hope this helps.
Peter
It's my understanding that both absorbtion and diffusion are required for good sound reproduction. I'm right in the process of doing the same as you are in my house and have adopted for a live end dead end (LEDE) approach as briefly described in this link;
What is "LEDE - Live End, Dead End - inSync"? | Sweetwater
I'm also constructing the diffusors as detailed in this link;
Depot Diffuser construction
Hope this helps.
Peter
That's definitively not the way I intended to go. Don't have enough $$$ to shell out on some fancy stuff like that!
I'll give it a try (lots of new words I've never used before): The OSB on the inside is acting as a vapor barrier and all the seams are sealed with lots of sticky tape. It is mounted directly to the rafters. On the outside of the rafters is a wind brace band and soft fiberboard. On top of that comes the battening and then the roof tiles. The space between the rafters is filled up with loose-fill insulation (made out of old newspapers, judging by the look of it).
Hi Peter, how would you position such diffusers in a room like mine? Is it okay to hang them on the walls, as slanted as they are? Or would they only be effective at the rear wall, which is the only straight wall in the room and thus already occupied by a bookshelf and a dart board...
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I think that the point is not how expensive the absorption panels are, but the percentage of the walls/ceiling that needs to be covered to kill off the side wall "slap". Basically, wherever you put your listening chair, you'll need just about 100% angled wall coverage with absorption from the front wall to the listening position to get a space that will permit any sort of critical listening. You'll also need almost 100% bass trapping of ceiling and floor/wall corner boundaries and a fairly well covered rear wall.
How you choose to do that is entirely up to you.
If you did not like the message of my posts (which were based on helping a friend with essentially the same shaped room iteratively add panels to solve the problem using measurements and listening), then please ignore them and pardon my intrusion. I thought that you were looking for help in how to handle the acoustics in your room. I guess that I was mistaken...
Chris
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Chris,
please excuse me if my reply sounded a bit harsh. Of course I appreciate your help and you're probably right with what you wrote. It's just that the photo you posted here scared me off a bit already, and reading through the rest of the forum post made me think 'thats not what I want for me'. That guy uses a DSP, whereas I enjoy building analog stuff. He shelled out a boatload of cash for a ruler flat frequency response, where I'm just looking to achieve a somewhat better sound with little extra material and a bit of DIY effort. My room is not solely for listening to music (or a recording studio), so I can't and won't sacrifice most of the walls for absorbing or diffusing stuff.
But then again, the takeaway message of that post might be that those two things (better sound and not sacrificing too much space) might not be possible at the same time. Therefore it's great to know what I might experience along the way!
please excuse me if my reply sounded a bit harsh. Of course I appreciate your help and you're probably right with what you wrote. It's just that the photo you posted here scared me off a bit already, and reading through the rest of the forum post made me think 'thats not what I want for me'. That guy uses a DSP, whereas I enjoy building analog stuff. He shelled out a boatload of cash for a ruler flat frequency response, where I'm just looking to achieve a somewhat better sound with little extra material and a bit of DIY effort. My room is not solely for listening to music (or a recording studio), so I can't and won't sacrifice most of the walls for absorbing or diffusing stuff.
But then again, the takeaway message of that post might be that those two things (better sound and not sacrificing too much space) might not be possible at the same time. Therefore it's great to know what I might experience along the way!
I think you acknowledge it's not an ideal space, however, many problems can be mitigated by lowering the listening volume. If you want to listen at medium to high levels I think you're going to have problems getting that room to sound right without a lot of treatment
I'm actually listening at pretty low volumes most of the time. My wife doesn't like most of my music, so being any louder than her watching TV is not an option.
Funny thing is that I like the sound better when actually listening with higher volumes (while wife's not at home) and sitting rather close to the speakers. Probably due to the reflected sound being drowned by the direct sound waves. Or the thrill of doing something not appreciated by wife and neighbours, who knows... Unfortunately that's not an option for everyday listening.
Funny thing is that I like the sound better when actually listening with higher volumes (while wife's not at home) and sitting rather close to the speakers. Probably due to the reflected sound being drowned by the direct sound waves. Or the thrill of doing something not appreciated by wife and neighbours, who knows... Unfortunately that's not an option for everyday listening.
The reason why I posted in this thread is due to the general lack of experience in using attic rooms shaped like yours.
I initially thought, like many others, that a few absorption panels along the side walls (similar to a shoebox-shaped room requires) would be enough. It turns out that the canted side walls introduce quite severe side reflections that are early reflections (the type that really destroy imaging). I was surprised by this, and now have come to understand why shoebox-shaped rooms are necessary for good sound reproduction. Canted walls create real acoustic problems.
The thread that I showed wasn't the first one that I've run into. In fact, its about four rooms that are similar in shape, all having equally obnoxious acoustic issues. The thread that I posted the link to just was the first one that showed what level of absorption was required for the guy that owned that room. His level of commitment was high, and his pocketbook was thick (it's thinner now...), and his tolerance for overdamped rooms a bit higher than mine, but not too much so. In other words, it would take me almost as much absorption to deal with the early reflection issues.
If the dimensions of the room were 2x or 3x larger (like a church sanctuary), then there would be no problems. It's the combination of small dimensions and canted walls that are the problem.
YMMV.
Chris
I initially thought, like many others, that a few absorption panels along the side walls (similar to a shoebox-shaped room requires) would be enough. It turns out that the canted side walls introduce quite severe side reflections that are early reflections (the type that really destroy imaging). I was surprised by this, and now have come to understand why shoebox-shaped rooms are necessary for good sound reproduction. Canted walls create real acoustic problems.
The thread that I showed wasn't the first one that I've run into. In fact, its about four rooms that are similar in shape, all having equally obnoxious acoustic issues. The thread that I posted the link to just was the first one that showed what level of absorption was required for the guy that owned that room. His level of commitment was high, and his pocketbook was thick (it's thinner now...), and his tolerance for overdamped rooms a bit higher than mine, but not too much so. In other words, it would take me almost as much absorption to deal with the early reflection issues.
If the dimensions of the room were 2x or 3x larger (like a church sanctuary), then there would be no problems. It's the combination of small dimensions and canted walls that are the problem.
YMMV.
Chris
Thanks again for sharing your insights here! Good to know that you've found several similar cases and can now draw this conclusion. Most of what I've come across so far stated that the slanted walls would make the calculation of room modes basically impossible, but otherwise 'the basic rules apply', whatever that means...
Taking into account that somewhat heavy treatment is necessary for a room like mine, what would you think of my proposal? Covering the upper two thirds of both slanted walls, down the whole length of the room, with rigid fiberglass as absorbent, seems like a lot already. Of course it's not as sophisticated (and not as expensive!) as in your linked thread, but maybe effective, too? Worst thing I could imagine would be a mostly dead and overdamped room, but I think that the floor and several other things like the window, a workbench and some more clutter would counter that to a fair amount. Maybe a diffuser or two at the rear end might help with that, too.
Regarding diffusers: Do they always have to be aligned towards the listener? What about hanging them onto the slanted walls, at the rear end of the room, basically pointing them into the middle of the room and downwards?
Your idea sounds like a good start, and perhaps will meet your needs. If you need to add more later, you can certainly do that as budget allows. If the absorption coefficient of the fiberglass is not high enough from 100-500 Hz, then you could attach added fuzzy material to the fiberglass to increase its effectiveness in this frequency band. Fuzzy comforters or old blankets could do in a pinch. It's not the cost of the material that counts, it's the acoustic effectiveness and how much you can tolerate its appearance. I'm a believer in doing things in the most cost effective manner.
I don't believe that there is enough room to add diffusers that are effective enough down to 200 Hz (or so). They would be fairly expensive, too, if effective enough down at lower frequencies and up to ~2 kHz. I've found a lot of people talking about diffusion, but when they actually get around to measuring its effectiveness, it turns out that it stops being effective around 200-300 Hz. This is too high of frequency, especially for such a small room where almost every reflection is going to be within 0.7-5 ms (the definition of "early reflections").
If all this absorption cuts down too much on the feeling of acoustic space (it will cut some no matter how much you try to avoid it), consider adding a little reverberation or using a high output impedance amplifier (tube type, etc.) to add apparent depth and breadth of the stereo image. This is usually the trade off--unless you're using a 5.1 (or higher) system with surround channel delays of 20-40 ms or more that are outside of the Haas integration interval.
Also, there is the option of suspending the loudspeakers from the side walls, instead of on the floor, I'm not sure what can be accomplished by this, but it's worth trying to cut down on the costs of acoustic treatments. Carpet remnants may be cheapest of all to absorb, and suspending the loudspeakers higher may be one way to do this. It depends a great deal on your listening position (height off the floor). It also depends on the directivity of your loudspeakers. Narrower is better--even down below the Schroeder transition frequency for the room.
I don't believe that there is enough room to add diffusers that are effective enough down to 200 Hz (or so). They would be fairly expensive, too, if effective enough down at lower frequencies and up to ~2 kHz. I've found a lot of people talking about diffusion, but when they actually get around to measuring its effectiveness, it turns out that it stops being effective around 200-300 Hz. This is too high of frequency, especially for such a small room where almost every reflection is going to be within 0.7-5 ms (the definition of "early reflections").
If all this absorption cuts down too much on the feeling of acoustic space (it will cut some no matter how much you try to avoid it), consider adding a little reverberation or using a high output impedance amplifier (tube type, etc.) to add apparent depth and breadth of the stereo image. This is usually the trade off--unless you're using a 5.1 (or higher) system with surround channel delays of 20-40 ms or more that are outside of the Haas integration interval.
Also, there is the option of suspending the loudspeakers from the side walls, instead of on the floor, I'm not sure what can be accomplished by this, but it's worth trying to cut down on the costs of acoustic treatments. Carpet remnants may be cheapest of all to absorb, and suspending the loudspeakers higher may be one way to do this. It depends a great deal on your listening position (height off the floor). It also depends on the directivity of your loudspeakers. Narrower is better--even down below the Schroeder transition frequency for the room.
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Well I look at that space and think "At least there aren't any parallel surfaces." 
. I suppose the front and the back wall are, tho. Still, not having the walls, ceiling and floor parallel is a good thing. And at least it's not gypsum board or concrete.
I agree with what's been said about stuffing the corners, and you'll want a combo of absorption and diffusion on the walls. Somewhere there is an old thread where I show how I built inexpensive panels of plywood, masonite, fiberglass and upholstery fabric. Worked great. Bill Waslo has a more recent thread about affordable home made diffusers.
A combo of those should give you a jolly good listening space.
. I suppose the front and the back wall are, tho. Still, not having the walls, ceiling and floor parallel is a good thing. And at least it's not gypsum board or concrete.I agree with what's been said about stuffing the corners, and you'll want a combo of absorption and diffusion on the walls. Somewhere there is an old thread where I show how I built inexpensive panels of plywood, masonite, fiberglass and upholstery fabric. Worked great. Bill Waslo has a more recent thread about affordable home made diffusers.
A combo of those should give you a jolly good listening space.
Hi again,
First, I'm only saying this because I hate to see you put something together only to regret it later.
OSB is not a vapour retarder. It is likely that condensation will occur partway through the insulation or on the underside of the fibreboard unless there is an air gap between it and the insulation and there is both air intake and exhaust for that gap. The amount of moisture that can get through even the best OSB, will not likely vent well enough through the fibreboard or through the gaps in the tiles. I am guessing the original vapour retarder and insulation is under the floor of the attic? If so you have now set up a second source of moisture and little means of venting it.
If I am getting something wrong with your structure, forgive my intrusion.
First, I'm only saying this because I hate to see you put something together only to regret it later.
OSB is not a vapour retarder. It is likely that condensation will occur partway through the insulation or on the underside of the fibreboard unless there is an air gap between it and the insulation and there is both air intake and exhaust for that gap. The amount of moisture that can get through even the best OSB, will not likely vent well enough through the fibreboard or through the gaps in the tiles. I am guessing the original vapour retarder and insulation is under the floor of the attic? If so you have now set up a second source of moisture and little means of venting it.
If I am getting something wrong with your structure, forgive my intrusion.
According to several simulation programs, a diffuser effective down to 200Hz would have to be half a meter thick/deep and should be placed several meters back from the listener.
Could you please elaborate on that? Does that mean that a diffuser must be effective down to 200Hz or lower to be of any benefit (in my case, that is), and thus a diffuser for, say, 600Hz and up would'nt be of any help? Somewhere else I've read that diffusion at such low frequencies doesn't make any sense in small rooms at all, so I'm a little confused now.
I hate gypsum board...
Yes, Peter posted that one already. I'll have to re-calculate it for metric wood strips, though.
What about covering up all of my side walls with those instead?
Very kind of you, much appreciated.
That's true, under the attic floor there's a foil layer. According to the contractor this foil was not needed on the attic, because of the OSB. Was that wrong?
Takeaway message for me is that putting rigid fiberglass directly to the outer walls is a bad idea. Leaving a little room of a couple centimeters would be fine I guess, but that would increase the complexity by a fair amount, so I could just as well build individual diffusers and hang them on the wall individually.
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