My soffit plans

Hi Folks, this year I want to build a new speaker wall. Maybe someone has some tips. I want to put the speakers into a wooden box, put it on (yellow) Sylomer. The space between the boxes will be filled with rockwool. Under the speakers there will be hangers for bass absorption. Does anybody know if the Klein&Hummel O300 are good for soffit mounting?

Those would probably work fine...in the manual there are settings for the eq response for flush mounting. I would be carfeful about airflow with those, you don't want them overheating!

Hi What kind of material do you want to use for the Soffitwall? It is recommendebal to use hevy and stiff material for the wall, to be shure that the wall won`t act as a membrane. I used 38mm HDF a few times with good succes. I also reccomed to ask K&H for their ideas about decoupling and also for ventilation volume of the soffitwall. The bassboost in the lowend won`t hurt you much, because your ear will get used to the sound after a short time, and you can also set the bassadjustment an the rear of the speaker. It will be usefull to calculate the size of the ventilation holes carefully to avoid a unwanted helmholz effekt. Wie schaut es denn mit deinem Großen Umbau aus? cheers Mika

That´s what I thought. 38mm MDF and 10cm wood for the stands. The O300 are on my wishlist, so I will build the wall big enough to fit for them.

That´s what I thought. 38mm MDF

Why MDF?? I`d prefer HDF because of it`s greater stiffness. A good source to order finishes cutted HDF is the comapny of friend: http://www.otto-schneider.de/ cheers Mika

A couple of comments: Is your SketchUp model to scale? If so, then it looks like your speakers are mounted very high, well above the usual 1.2 m recommendation, and seem to be firing way over your head. Or maybe it's just the angle of the image? The other thing I noticed is that you seem to have your speakers intersecting at 90 degrees. Is that correct? There's nothing wrong with that, but you usually only need to do that if you have a really shallow room, in order to get the mix position right. Is that why you tightened up the angle? - Stuart -

Stuart, youre right. I wanted to put it on 1,2m, its now and 1,5 and too high. The angle is 30degrees, the front wall is the one with the window.

mika wrote:

That´s what I thought. 38mm MDF

Why MDF?? I`d prefer HDF because of it`s greater stiffness. A good source to order finishes cutted HDF is the comapny of friend: http://www.otto-schneider.de/ cheers Mika

You need MASS, not stiffness.

You need MASS, not stiffness.

Mass is one faktor, stiffness another, and both are important, as i wrote before. HDF (750 kg/m³) has a greater stiffness , and a higher mass than MDF (640 kg/m³) so it`s a good choice. cheers Mika

Yes, stifness is another factor. But you need LESS stiffness and more mass. Hence LEAD sheets are great isolators. Big mass, and flexible (less stiffness). a 60cm stud spacing also works better than a 40cm spacing since the latter will make the wall more stiff.

Yes, stifness is another factor. But you need LESS stiffness and more mass. Hence LEAD sheets are great isolators. Big mass, and flexible (less stiffness). a 60cm stud spacing also works better than a 40cm spacing since the latter will make the wall more stiff.

We are not talking about soundisolation, we are talking about building a Soffitwall, which has not to resonate as a membrane. From my view, in this case the mass of the wall sets the resonantfrequency and the stiffness the amplitude of the resonating. Can you also explain me, why when stiffness is bad for isolation, a brickwall (also a ytongwall) has a better TL in the bassfrequency ,than a one leaf studwall with the same mass?? cheers Mika :D

Wasn't aware of the topic being about creating a speaker soffit wall. But same principles apply here. A stiff material is easier to resonate. A stiff material will give back more energy on impact. But (sound)waves travel much easier through a hard material than a soft one (aka flanking) Tho, at low frq there's no stopping the waves. Stiffness is effective at low frequencies due the fact that the (sound)wave must push against the stiffness of the material. We're talking stifness controlled isolation at this point. As frq rises, and nearing it's own resonance, the stiffness becomes less effective since there's less distance needed (shorter waves) to move the material and radiate sound. At resonance the MASS law steps in, taking over the stiffness controled isolation. More "force" is needed to move that same material at a same distance. To avoid "flanking" you can use less stiff material (since stiffness is no longer a factor). With a soffit wall you want your wall resonance as low as possible (less obvious to hear the buzz..) so you want mass. doubling the mass will add about 3dB of TL but the resonance will drop too. If you want it really low, use a concrete wall (mass). Is that practicall? dunno, we have to wait and see what Stuart makes of it (still planning on doing a concrete soffit wall, Stu?) Making a heavy wall resonate, it needs force. Low frequency for example. If we don't need it for isolation we don't need the stiffness controlled isolation region and we don't want the wall to resonant easy, so why not make the wall as heavy and flexible as we can? I'm sure ROD or Eric has got a thing or two to say on this matter as well, I'm just an "overnight expert" as John pointed out so elegantly.

Is that practicall? dunno, we have to wait and see what Stuart makes of it (still planning on doing a concrete soffit wall, Stu?)

Yup! You bet! I figure its the best possible mass I can get, since I cant find a supplier of sheet uranium around here.... :) I guess I could go with lead sheet, but that stuff is damn expensive compared with concrete.

So why not make the wall as heavy and flexible as we can?

Good point! How can I make flexible concrete? :) But your comment did get me thinking: Would there be any point to gluing a couple of layers of MLV on the front of my concrete, for that very purposes? Give the front face some flexibility and a little mass, with some serious but less flexible mass behind it? I mean, surely, there must be SOMETHING that MLV would be good for! ( :) )

...I'm just an "overnight expert" as John pointed out so elegantly.

You and me both, but you are one hell of lot more "expert" than I am! Streets ahead. Different ballpark. If I could even get to understand half the stuff you know about acoustics, I'd be a happy camper... - Stuart -

Yeah, there MUST be something good about MLV. It's a great giftwrapper prolly :lol: Neh, better add wool instead on the front to get rid of nasty reflections (dunno about that) I'm really looking forward to your plan/construction of that concrete speaker wall. down side is that you'll have to soffit your CURRENT monitors in the concrete. So, if you're ever gonna spend some precious money on another set of speakers..... I'm not even NEAR the "expert" as some other folks I could mentioned (hai John :) ) are. I've been studying acousics only for a year or 5 or 6.

I found in another thread this picture. Soffit mount into glass wall. Seemed to be very stiff...

Neh, better add wool instead on the front to get rid of nasty reflections (dunno about that)

I think wool would be too light. Maybe lead? A think sheet of lead would probably be good. Not sure about aesthetics, though! I think I'm going to look into lead again, and see how much it actually costs here, now that the metals markets have crashed...

I'm really looking forward to your plan/construction of that concrete speaker wall.

Working on it! There are some rough outlines on my design thread, but I'm still refining those. Basic idea is a sand-filled steel framework bolted to the floor, and threaded rod to allow adjustments of the soffit panels.

down side is that you'll have to soffit your CURRENT monitors in the concrete. So, if you're ever gonna spend some precious money on another set of speakers.....

I just spent a few thousands dollars on a nice set of Adam A7s and a Sub-8 to go with them, especially for this specific studio! So I hope I don't have to change them any time soon.... But if I do, it will just be a matter of loosening off the threaded rod, taking of the entire panels, and replacing them with new panels specially formed to fit the new speakers. Concrete is cheap enough that I don't mind having to re-cast panels for different speakers. Hopefully, I'll be posting an updated design of my studio in a few days, for comments, flames, sanity check, and suggestions. I'd really like your opinion on it! - Stuart -

A stiff material is easier to resonate. A stiff material will give back more energy on impact. But (sound)waves travel much easier through a hard material than a soft one (aka flanking) Tho, at low frq there's no stopping the waves. Stiffness is effective at low frequencies due the fact that the (sound)wave must push against the stiffness of the material. We're talking stifness controlled isolation at this point. As frq rises, and nearing it's own resonance, the stiffness becomes less effective since there's less distance needed (shorter waves) to move the material and radiate sound. At resonance the MASS law steps in, taking over the stiffness controled isolation. More "force" is needed to move that same material at a same distance. To avoid "flanking" you can use less stiff material (since stiffness is no longer a factor).

Thanks for this information. Do you know additional sources for finding more technical info about these relationships?? cheers Mika

Yes, there's good books about acoustics. The "bible": Master Handbook of acoustics (Everet) And Acoustics and Psychoacoustics (Howard, Angus) for example...

So, this year is the year... Right now I built a small tracking room. Its working very fine, I will post it in another thread. With these experiences I am really excited and looking forward to rebuild the main mix and mastering room. In this room I want to soffit mount the speakers. Still I am not sure which speakers I want to use. Maybe PMC or KSdigital. So I will build a box into the frontwall, where I can fit in different speakers. My big question: The wall around the speakers must be from drywall or from fabric? If its drywall, is there a need for hangers, wont they be useless behind the drywall? How can sound reach the hangers then? Edit: this was the other thread about the room.... http://johnlsayers.com/phpBB2/viewtopic.php?f=1&t=11111

there's a sticky in this forum called "small studio in 3D" download the .skp file and check out the soffit mounting construction.

My big question: The wall around the speakers must be from drywall or from fabric? If its drywall, is there a need for hangers, wont they be useless behind the drywall? How can sound reach the hangers then?

I'm looking at your question and also at your model, but the two don't match! Your arrow on the diagram, labeled "Fabric or Drywall" is NOT pointing to the soffits! It is pointing to the center panel BETWEEN the soffits. So I'm not sure what you wanted to know... But anyway: in your diagram, your soffits (the panels with the speakers in them) do not seem to be wide enough to be very effective. They need to be as wide as possible, 48" being ideal. Yours don't seem the be more than a few inches wider than the speakers themselves. You should probably fix that. Regarding the material for the soffit panels (the panels with the speakers in them). IT needs to be solid, dense and massive. Something like thick plywood or MDF is fine. I am planning to cast mine in concrete. So cloth is definitely out of the question! Having said that, as you move further away from the center of the speaker on teh soffit panel, the solidity and density becomes less important, so theoretically you could change to another material far away from the speaker, but it does no harm to keep it all solid and massive. Finally, regarding your center panel question: In fact, that can be whatever you need it to be, in order to correctly treat the acoustics in your room! Not much of an answer, I know. Most likely you'll want to cover that area with absorption, to deal with reflections coming off the back of the desk and console. But you can also use the SAME area as a bass trap with hangers, like John does. To do that, you'd have a panel of plywood / MDF or something like that in front of the hanger chamber, you'd leav a one foot gap at the bottom of the panel so the sound can get into the hangers (in other words, the panel does not go all the way to the floor). Then you'd cover the front of that panel with absorption. That way, you kill two birds with one stone! (If you don't want to see the gap at the bottom, you could build a frame around it and put cloth over it.) You can also do the same in the bottom section of the actual speaker soffits: create hanger space below, leave a gap at the floor, and cover the lower front of the panel with absorption. But once again, don't take the absorption too close to the speakers themselves: You do want at least a couple of feet of clear hard, massive surface around the speakers. And take a look around the forum: you'll find several designs for speaker soffits, most of them based on John's designs. You can most likely adapt some of those to your situation. - Stuart -

EDIT: Ups, Stuart was quicker... Stuart, thanks. I will start from scratch a new design and post it here. Thanks, mate,

Just to see if I understand it in the right way, heres a next rough sketch. I angled the frontwall 30 degrees, they are from drywall, with a tunnel for bassabsorption. Behind the frontwall I want to put in hangers, in the middle just 10cm glas- or rockwool. The ceiling will be raising to the back, on the reflection spot maybe i put a skyline diffusor The side absorbers I will make as slatpanels. On the backwall maybe in the middle a Schröder-Diffusor and in the corners (backwall) helmholtz or superchunks. Is the direction better to go?

These might suggest something to you.

But anyway: in your diagram, your soffits (the panels with the speakers in them) do not seem to be wide enough to be very effective. They need to be as wide as possible, 48" being ideal.Yours don't seem the be more than a few inches wider than the speakers themselves.

Apparently, since he designed this whole studio, and had the option, Mr. Latchot isn't aware of this. You should inform him. Oh, about the fabric thing too...

hey, g slam, or anybody... can you point me in the direction of that thread with soffit mount into glass wall please... :D