I'm building a 5.1 edit/mix studio in a decidedly difficult room. I've already soundproofed the room by building an entirely new room within the existing one. The new walls are about 4" from the old ones and are made out of 2 layers of 5/8" sheetrock with a layer of green glue in between. The floor is concrete and will probably stay that way, albeit with an area rug or two laid down.
The dimensions are kinda evil: 15 L x 7'5" W x 10' 11" H. It definitely has a boxy sound, live...but not in a good way. Just talking to a friend in there today I heard my voice drop off precipitously around 100 hz in various places.
This being said, I think it makes sense to soffit mount smaller monitors in the corners because if I don't, the damn narrowness of the room makes severe wall interaction inevitable. Talking to my friend today we came up with an interesting idea in this regard. Since we were already going to build 8 foot tall 703 or rockwool-based superchunk broadband absorbers in the corners, why not just make room for heavy mass-loaded stands in the middle of them and then and cut a hole in the insulation for the speakers baffles to be free from obstruction?
My plan is also to continue the bass trap so that it follows the front wall and similarly soffit mount a center speaker there.
The designs I've seen about soffiting speakers call for tightly enclosing them in boxes and extending their baffles by having a hard surface extend away from the existing baffle, and I understand why this would work in a bigger room creating a LEDE. But since this room is so oddly shaped and since I can't do anything about that, what do you think about this idea?
In addition to the superchunks, I plan on erring on the side of dead-ness and building quite a number of different sized 4" broadband absorbers.
Thanks for your advice and for the great site!
Opinions, thoughts about this superchunk/soffit combo idea
Originally posted at johnlsayers.com, topic 17287.
Hi "bias". Welcome!
:shock: As you said! "Evil". Since one dimension is almost exactly twice the other, you will have major modal problems in there: every second order mode of the width will line up nearly perfectly with ever first order mode of the length, across the entire spectrum. If possible, it would be good to deal with that. At least you have good height!The dimensions are kinda evil: 15 L x 7'5" W x 10' 11" H. It definitely has a boxy sound,
Yup. You were probably standing in one of the modal nulls for a couple of frequencies around there. You have quite a collection of modes around there: 91.4 hz 2,0,1 Tangential 92.1 hz 0,1,1 Tangential 99.5 hz 1,1,1 Oblique 103.5 hz 0,0,2 Axial 107.1 hz 2,1,0 Tangential 110.1 hz 1,0,2 Tangential 113.0 hz 3,0,0 Axial But that's not what you were hearing: the human voice puts out very little useful energy below about 150 Hz, so if you were just talking, then most likely you were hearing issues much higher up the spectrum that you confused with lower subharmonics, or some such.Just talking to a friend in there today I heard my voice drop off precipitously around 100 hz in various places.
SBIR is inevitable in small rooms anyway, but soffits always make sense. However, the monitors shouldn't be too small: they need to be the right size for the room, neither too big nor too small, and the soffits need to be the right size for the monitors and for the room.This being said, I think it makes sense to soffit mount smaller monitors in the corners because if I don't, the damn narrowness of the room makes severe wall interaction inevitable.
That's not a soffit! That's just a speaker stuck in the middle of a pile of absorption. Technically, a soffit is an infinite baffle across the entire operating spectrum of the speaker, so it has to be very massive, very rigid, and large enough to cover the lowest range produced by the speaker. (Or at least, as large as the room will allow).Since we were already going to build 8 foot tall 703 or rockwool-based superchunk broadband absorbers in the corners, why not just make room for heavy mass-loaded stands in the middle of them and then and cut a hole in the insulation for the speakers baffles to be free from obstruction?
Same problem. 5.1 is a bit more complex than normal 2.0 or 2.1. There are numerous other issues that you need to take into account. Both the ITU and EBU have very specific recommendations for all parameters of a 5.1 room. It's hard to do right, even in a large space, and still more challenging for a small space. You CAN combine a soffit with bass trapping, but not in the manner you describe.My plan is also to continue the bass trap so that it follows the front wall and similarly soffit mount a center speaker there.
That has nothing to do with the size or shape of the room, nor even with LEDE design (which hasn't be used as such in years anyway!). The baffle extension is the entire point of the soffit. It forces the speaker to radiate into half space, instead of full space. It also eliminates all of the issues with comb filtering, phasing, reflections and other nasty artifacts coming off the front wall. It tightens the bass response, creates a clean, clear, broad, precise stereo image and sound stage, and does other good things. It also creates a 6 dB boost in the bass response, which means that you should choose speakers design for soffit mounting, which have bass roll-off controls to compensate for that. Or you can use some form of tuned filter to do the same job, such as the one designed by Barefoot, that you can find on here. So soffits will work in any size room. Even in John's famous "studio in a shipping container" he did soffits, for the very same reason: it would have been dumb to NOT do them! But soffits have no relationship at all to LEDE. LEDE is a concept whose time came and went twenty years ago, and has been replaced with things like RFZ and CID, which are extensions and variations of LEDE, to a certain extent. Soffits can indeed be part of a good RFZ design, but you can also do RFZ without soffits, and soffits without RFZ.The designs I've seen about soffiting speakers call for tightly enclosing them in boxes and extending their baffles by having a hard surface extend away from the existing baffle, and I understand why this would work in a bigger room creating a LEDE
I wouldn't aim for a dead room! Dead rooms are unpleasant to work in, and fatiguing. Instead, I'd aim for the right amount of bass trapping for that room (which will be "lots", since it is a very small room!) but without losing the high end. The goal of a control room design should be neutral response and RT-60 within the recommended times for each band, as suggested by ITU (and EBU). (Especially for a 5.1 room!) In your case, that means around 340 sabins of absorption, give or take a few dozen (depending on other design issues!) Building different size absorbers that are all the same thickness means they will all treat the same frequency range. Probably not a good idea. Much better to distribute the absorption in a more conventional manner, with deep bass trapping in the corners and across the rear wall (perhaps hangers? you have enough room length, I think), plus broadband treatment on the walls, and other devices as needed. That would be my approach. - Stuart -In addition to the superchunks, I plan on erring on the side of dead-ness and building quite a number of different sized 4" broadband absorbers.
Thanks for all the great advice. Here's another hypothetical that I'm hoping you could speak towards:
As I understand it the main (only?) benefit from soffits is that when applied, the energy from the speaker does not wrap around the edges of it's enclosure, bounce off nearby reflective surfaces behind and adjacent to it, and then hit the engineer thereby creating all sorts of phase cancellation and nastiness.
If that's true, then wouldn't covering the walls behind and adjacent to the speakers with 4" Fiberglass board (which according to John's recording manual has an absorption coefficient of .99 from 125hz through 4khz create the same (or nearly the same) result as had you soffitted the speaker?
Aside from artifacts created from the speaker's own baffle and enclosure I don't see a difference between doing this and soffiting. It might actually be a net benefit as you're using the speaker as the designer intended and don't have to introduce LF filters. And it would be a lot less labor and cost intensive.
Thanks so much for your input.
Well, yes and no. The soffit does prevent low frequency energy (ie, energy of all wavelengths that are larger than the speaker cabinet itself) from wrapping around, which is what I said in my previous posts: it forces the speaker to radiate into half-space (2-pi space) instead of full space (4-pi space). The key words here are "low frequency" and "long wavelength". We'll get back to the implications of that later, but basically any wavelength that is shorter then the dimensions of the speaker CABINET itself is forced into 2-pi space. Any wavelength LONGER than the dimensions of the speaker cabinet remains in 4-pi space. So the effect varies according to frequency, and there is a transition region where wavelengths are progressively to a greater extent as the frequency goes down: it's not a sudden sharp cutoff, but rather a gradual roll-off, that once again is affected by the size and shape of the cabinet. Note the term CABINET. Speakers are designed with cabinets around them for many reasons, and this is one of them; to focus the sound forwards as much as possible. The bigger the cabinet, the better it does that. But there are practical limits on how big you can make a cabinet: the bigger it is, the more expensive it is to make, package and ship, for example. Small speakers fit nicely in houses, while big ones don't. blah, blah, blah. There are many reasons for limiting the size of a cabinet, but the point is that if a speaker cabinet could be made infinitely large, or at least much larger than the longest wavelength (lowest sound) that the speaker can reproduce, then it would be directional at ALL frequencies: Everything would be directed forwards, focused into the room. There would be no edge diffraction, and no wave "wrapping around" behind the speaker. So what's the problem with waves wrapping around? As you mentioned, you can get reflections off the front wall, comb filtering, phasing, timing issues, etc. All those nasty things. But there's another reason, too: If longer wavelengths all go forwards into 4-pi space, and shorter wavelengths wrap around into 2-pi space, then there is obviously a large power imbalance in the speaker. ALL of the power output by the speaker in the higher frequencies goes forwards, while only HALF of the power in the lower frequencies goes forwards: (the other half goes backwards, where it is usually absorbed, reflected, diffused, interferes with itself, etc.). So all of the higher frequencies are getting a 6 dB boost, while all of the lows are not: they are 6 dB too low in power! So what do manufacturers do? They deliberately skew the response of the speaker with an internal circuit that adds 6 dB to the lower frequencies (lower than the baffle step point). If the speaker is soffit mounted, that circuit is no longer needed, and the power balance is automatically restored: the speaker now has more consistent power characteristics, and can do its job correctly, in a more linear manner, without wasting half the power in the lows with all the issues implied by that. So soffits restore power balance as well, and that's a biggie! Soffits do many good things, not only "preventing energy from wrapping around". Yes, that's what they really do, at the most basic level, but the consequence are much more far reaching than most people imagine. So why will your idea not work? Think of it this way: You are basically saying that if you take any great studio monitor, and remove the front panel and side panels, then it will sound much better!.... Think about that. That's the exact same concept as what you propose: You say that building a soffit without a front panel or side panels, just with absorption, will cause the speaker unit to perform "as the designer intended". ... :!: Do you REALLY think that a great speaker would sound better if you took the cabinet off, leaving only the insulation? And that were the case, then why do manufacturers spend such huge amounts of time and money to design, engineer, test and manufacture cabinets for their speakers? Why don't they jut build cubes of insulation with their drivers embedded in the middle? In essence, your suggestion of building a soffit only with insulation and no panel is exactly equivalent that: remove the box from a great studio monitor, leaving only the driver surrounded by the insulation. Obviously, that would not work: such a speaker would sound terrible. In reality, it is the other way around. Speakers need LARGER boxes, not NO boxes. And a soffit is nothing more than a larger box for the speaker. That's all it is. So if a speaker sounds terrible with no box, and good with a small box, it should sound great with a large box. And yes, it DOES sound great with a large box, when the "large box" is correctly designed and built as a soffit.As I understand it the main (only?) benefit from soffits is that when applied, the energy from the speaker does not wrap around the edges of it's enclosure, bounce off nearby reflective surfaces behind and adjacent to it, and then hit the engineer thereby creating all sorts of phase cancellation and nastiness.
No, because there is no surface, no mass, and no rigidity! Speaker manufacturers go to great lengths to ensure that their cabinets are hard, solid, rigid and massive. If they could build them out of just plain old fiberglass board with a hole in the middle, don't you think they would do that? A lot easier and cheaper! So why DON'T they? Once again, we get back to mass, density, rigidity, etc. There are very, very few ways to stop a sound wave getting from point "A" to point "B". One way is to remove all physical media between "A" and "B", by creating a total vacuum. ("In space, no one can hear you scream"). That's hard to do! Another way is to create an exactly equal but opposite wave to cancel out the first wave. Yet another way is to put an infinitely massive object in the way between "A" and "B": if the object has enough mass that the sound cannot move it, then the object stops the sound. The final way is to put an infinitely rigid object in the way between "A" and "B". If the object is so rigid that the wave cannot make it move, then the object stops the sound. That's it. There are no more ways to stop sound. So how do you stop the sound from wrapping around behind the speaker? You have to put a vacuum in the way (ummmmm... dunno how you'd accomplish that! :) ), or you have to add a second speaker that creates identical inverted waves, thus annulling all sound from the first one (which would kind of defeat the purpose of the speaker! :) ), or you have to put a massive surface in the way, or you have to put a rigid surface in the way. Wood is both reasonably massive and reasonably rigid, when it comes to sound waves. So are some types of high-density plastics, and other materials. That's why speaker cabinets (and soffits) are made if high density, massive, rigid materials. But fiberglass insulation is neither massive nor rigid, so it is useless as a baffle. It won't work precisely because it is soft, fluffy, light, etc.then wouldn't covering the walls behind and adjacent to the speakers with 4" Fiberglass board (which according to John's recording manual has an absorption coefficient of .99 from 125hz through 4khz create the same (or nearly the same) result as had you soffitted the speaker?
Sound is like water, and acoustic absorption is like a sponge. Can you mop up spilled water with a sponge? Sure you can! Can you put a sponge in front of a fire hose, and expect it to stop the flow? Obviously not! Even though it is highly absorbent, it can only deal with a limited amount of water at a time. Same with acoustic absorption: it is great at "mopping up" sound that spills into places where you don't want it, but it cannot stop a stream of sound from a speaker any more than a sponge can stop a stream of water from a fire hose. If you want to see how well a panel of 4" rigid insulation stops sound, go buy a piece of 4" OC-703 at your local hardware store, crank up your speaker to full power with loud rock music, and put the 703 panel directly in front of the speaker, up against the front panel. Does it stop the sound? Nope! Does it even make a large difference to the sound? Obviously, not. At best, it muffles some of the high frequencies a bit, but the lows coming booming through the same as ever, just like the water from a fire hose comes right through the sponge. That's why a "soffit" made of insulation would not work. It has grossly insufficient mass, and grossly insufficient rigidity. Sorry.has an absorption coefficient of .99 from 125hz through 4khz
There's a huge difference. Several orders of magnitude, actually. The density of the types of materials used to make speaker cabinets and soffits is in the region of a thousand kilograms per cubic meter. The density of fiberglass insulation is in the region of thirty kilograms per cubic meter, which is a difference of more than three orders of magnitude. You'd need thirty-something times as much insulation to get the mass, but you still would not have the density, nor the rigidity. Can you bend a piece of fiberglass insulation? Sure you can! Very simple. Even "semi-rigid" OC-703 is not really rigid at all, and is easily bent just with your hands, with no trouble at all. Can you bend a sheet of plywood or MDF an inch and a half thick? Ummmm.... :) The rigidity is vastly different from what is needed in a soffit.Aside from artifacts created from the speaker's own baffle and enclosure I don't see a difference between doing this and soffiting.
Actually, the designer is the one who had to add filters! He either had to reduce the HF power output by 6 dB, and build a filter to roll that off to 0 dB for the LF, or he had to increase the LF power output by 6 dB, and build a filter to roll that off to 0 dB for the HF. By putting the speaker in a soffit, you eliminate the need for that filter, and therefore you even out the power response of the speaker, back to the way it should have been. It is precisely the LACK of a large enough soffit that forces the designer to compensate for large loss in LF power output, by using filters and other tricks.It might actually be a net benefit as you're using the speaker as the designer intended and don't have to introduce LF filters.
I'm not so sure about that either! :) - Stuart -And it would be a lot less labor and cost intensive.