John Sayers' Recording Studio Design Forum Archive

As far as the soffit design - I was planning on doing something very similar to this thread:
http://www.johnlsayers.com/phpBB2/viewt ... t&start=45

What I cant figure out is what is sealed off since the center portion of his wall does not have the same layers of gypsum that the speakers walls do.

As far as the soffit design - I was planning on doing something very similar to this thread:

To be honest, I would not use that as a good example of well-designed soffits. There are several issues with the design, both of the soffits and also of the room itself, as noted in that thread.

What I cant figure out is what is sealed off since the center portion of his wall does not have the same layers of gypsum that the speakers walls do.

The soffits do not have to be sealed air-tight. Yes, they do need to be enclosed all around, but you have to punch huge holes in them to provide ventilation airflow for the speakers anyway, so there's no need to seal them hermetically. I normally just build a "box" all around each one, as deep as necessary to fit the speaker in comfortably, then leave the center section between the soffits for absorption, or some other treatment.

- Stuart -

Thanks again Stuart,

I think a while you back you had mentioned that you had design that may work in my situation, something you had done previously I think I messaged you about it . I was not planning on venting these Urei 813's . I went on a rant last night but in my previous posts I explained why - however I trust you advice on this so if I NEED to go vented I will.

Assuming I do not need to vent these, I still am having some trouble understanding the concept of the soffit, mostly because of a difference I see in the builds (John's and Barefoot's design) and the story/method that John described about how they used to test speakers by burying them in the ground.

When burying something in the ground - I fully understand that this would not only eliminate reflections from behind the speaker - but also FORCE the sound to only radiate from the front. A true half dome.

But these soffit designs seem to only paying attention to the PLANE right around the face of the speaker. In many cases these don't even seem to be THAt massive and rigid - I believe Johns design only calls for 5/8" plywood and a timber finish. I do understand that this helps. But is this really FORCING the speaker to only radiate forward? Isn't the speaker still radiating sound from the rear but we are just not hearing it since it is being absorbed and blocked by the soffit face? Is everything going on behind this soffit wall basically a tree falling in the forest and nobody is there to hear it?

I am trying to visualize a wall built entirely out of concrete , a solid wall, with the only openings being the exact size of the speaker so they sit flush. Assuming no ventilation is required - would'nt this be the best design? I realize that this eliminates the possibility of using some sections of the front wall as bass trapping - but Wouldn't this most closely simulate a speaker being buried in the ground? In this hypothetical scenario - would there be a need for any sort of trapping, insulation or treatment whatsoever BEHIND this wall?

In my current design, my speakers are not angled down at all, so it actually may be feasible to build a wall entirely out of concrete blocks, or maybe at least 2 large sections of the wall?

I guess this is not really a specific question but I feel like I am at the verge of understanding the soffit design concepts and it's bugging me that I am still so confused about so many things.

I also am wondering about the very small space that would result after putting soborthane pads underneath a speaker to decouple it from the box it sits it. Although this is only a very small space, isnt some of the sound from the bottom of the speaker box escaping forward?

The ornage-ish boxes around the speaker are going to be 3/4" MDF (2 layers) lined with soborthane (5mm) on the inside,

That wont work...

Sorbothane is great stuff (the best, actually), but that's not the way to use it. You need to carefully calculate the load that your speaker will place on the Sorbothane, calculate the correct deflection, and then check the resonant frequency and other parameters to make sure that the speaker really is floating inside the box. I can guarantee that it won't turn out to be a 5mm thick lining all around! It will probably be just a few small pads at strategic points on each side of the speaker. Doing the calculations takes time, and care. If you don't do it right, then the speaker won't float: it will be coupled to the box, and therefore to the soffit structure...

I just did a design for floating speakers this way for one of my customers, so I still have all the details fresh in my head. You will need thick Sorbothane, 50 durometer Shore 00, in several small pads.

The boxes will be sitting on soborthane or neoprene pads

See if this rings a bell: If you do that, you will have a mass (the speaker) resting on a spring (the sorbothane inside the box) resting on a mass (the box itself) resting on another spring (the sorbothane between the box and the concrete blocks) testing on another mass (the concrete blocks). So you will have a Mass-spring-Mass-spring-Mass system... In other words, that is the exact same situation as a 3-leaf wall. Unless you design it very, very carefully, you will end up with poor isolation in low frequencies... It can be done (I know, because I just did it for my customer), but there's a lot of math and careful design involved. You need to tune BOTH systems lower than you would for either by itself, then check that the COMBINED resonance is still below the lowest frequency of concern (at least an octave below the cut-off), an that both F+ an F- are still below that point.

Are these MDF boxes all it takes to direct/restrict the sound-field to a half-dome (180)?

The boxes that surround the actual speaker do very little, acoustically. Their sole purpose is to hold the speakers in place. Period.

What redirects the sound is the very large, flat, massive and rigid front baffles on the soffits. You don't show those at all in your diagram, so it's impossible to see if you are doing them correctly or not. Please add those to your model, and show the images again, so we can see if you are doing it right. Without front baffles, you don't have a soffit mount.

Or does the actual soft wall do some of that?

What do you mean by "soft wall"? There is no soft wall in a correctly designed soffit mount.

I know the front soffit wall - the one flush with the speakers - should be massive and rigid.

Correct.

However some of the designs I see on here, directly behind a thin piece of "bezel" wood there seems to be insualtion inside of framing (open to the back behind that of filled with more insulation).

I'm not sure which design you are talking about. Do you have a link to that? It's hard to discuss something that you can't see!

I guess I'm having trouble figuring out what areas to "seal" off -

The interior of the soffit does not need to be sealed. Indeed, it cannot be sealed, because there needs to be ventilation air flow up past the rear of the speaker (yes, there NEEDS to be that). Those speakers are sucking up a few hundred watts of electrical power, and concerting 99% of it heat. That heat needs to be removed. If there is no ventilation, the speakers will keel over and die, very soon. Speakers are NOT designed to be used without ventilation around them. If you are in doubt as to how much ventilation they need, ask the manufacturer.

I am NOT planning on venting these speakers in any way -

You must have lots of money to spare then, to buy new ones every few months, as the old ones burn out...

Your speakers are rated to absorb 200 watts of electrical power, continuous. Only about one watt of acoustic power comes out. The rest goes into heat. Enclosing those speakers inside a wooden box is almost the same as enclosing two 100w electric incandescent light bulbs in a box...

The boxes are cold always. Cold to the touch.

That's because right now all of the excess heat is radiated out through the cabinet walls. That's a very large surface area. When your speakers are soffit-mounted the way you want to do it, the cabinet surface area available for cooling will be zero. The laws of physics are immutable: if you pump 75 watts of power into that speaker, then 75 watts must come out. One half of a watt of acoustic power, and 74.5 watts of heat. That heat has to go somewhere!

Could I just box tightly around the speakers and the use the whole area behind the framing for trapping/treatment?

Yes you can, except for the small volume that you need for the ventilation path. That can be done with "chicken wire" that you shape to create a "chimney" for the air flow, around the back of the speaker cabinet.

So - to vent or not to vent?

You MIGHT be able to get away with not venting, but why run the risk? It is so easy to create the vents you need, there is no acoustic penalty, there is no aesthetic penalty, the cost is practically nothing... Why risk damaging your speakers, when there is no need to?

What is the basic reason you have for NOT wanting to ventilate? I really can't think of any valid reasons at all!


- Stuart -

Stuart!!! Thanks a million. you've convinced me - I SHALL VENT! These are really big boxes so I understand that the heat is dissipating over a large area which is why I cant detect it by hand or even temperature gun.

What is the basic reason you have for NOT wanting to ventilate? I really can't think of any valid reasons at all!

I guess I just was/am still not fully understanding the concepts and thought completely sealed would be better. Additionally thought it may be a little easier to build without the vent. But when you explain it that way it doesn't really seem like too much and better safe than sorry. Oh and being stubborn too did I mention that? lol - But I digress - I SHALL VENT

I just did a design for floating speakers this way for one of my customers, so I still have all the details fresh in my head. You will need thick Sorbothane, 50 durometer Shore 00, in several small pads.

Amazing, thanks again. I'll double check my weight loads, etc.. before I actually build but this is great info.

So you will have a Mass-spring-Mass-spring-Mass system

Ok so I will definitely NOT being lining the box AND doing the pads (M-S-M-S-M), I'll just stick to (1) layer of properly compressed "S"

What redirects the sound is the very large, flat, massive and rigid front baffles on the soffits. You don't show those at all in your diagram, so it's impossible to see if you are doing them correctly or not. Please add those to your model, and show the images again, so we can see if you are doing it right. Without front baffles, you don't have a soffit mount.

I posted that design up too early, I haven't even got to the front wall material yet although I was pondering 2 layers 5/8" with a finish wood over that. I have like 3 designs going at once - another one the whole wall is built out of CMU blocks. Another design has a corner control room design.

Stuart (or anyone who knows speakers). I think the answer to this question will help me understand the whole soffit design thing.

How does a speaker radiate sound 360 degrees? (see photo) please excuse my HORRIBLE quick sketch I think the answer to this will help me understand HOW the sound field is restricted to 180 degrees through soffit mounting. As a side note - I do understand the concept of edge diffraction and SBIR. It's more the concept of "Acoustical Loading" that I am struggling with

Quote:
However some of the designs I see on here, directly behind a thin piece of "bezel" wood there seems to be insualtion inside of framing (open to the back behind that of filled with more insulation).
I'm not sure which design you are talking about. Do you have a link to that? It's hard to discuss something that you can't see!

As far as the other designs - I was basically referring something like this: link here:
http://www.johnlsayers.com/phpBB2/viewt ... 1&start=30

Or John's design: link here:
http://www.johnlsayers.com/phpBB2/viewt ... &view=next


there's loosely packed insulation behind the wall, sometime I see hanging bass traps there too. Are these helping with the control rooms acoustics or are these helping damp down the sound emitting from the rear of the speaker? This is why I really need help with my question regarding HOW a speaker emits sound. Does it come FROM the rear? Also I am not seeing the "massive" front wall. 5/8" plywood and timber finish? If the box that goes around the speaker (assume made of 5/8" plywood) does little to block sound (and is for mounting purposes mostly), then how is this 5/8" plywood with timber finish blocking it? I also understand that the acoustic hangers BELOW the shelf in Johns design ARE for the Control Room acoustics, its mostly the stuff above I'm wondering about.

I've also seen some actual construction photos that show similar which I'll try to locate, but this is basically what I was referring too.


This is from "Somewhere" Studios I believe John designed. Although unfinished - you can see the speaker is almost already entirely flush with the front of the box meaning the Bezel - or "massive" front wall is only going to be millimeters thick. This guy used 2 layers of 3/4" MDF for the front walls - seems reasonable to me - but It's also what I suggested making my speaker boxes out of which Stuart mentioned does very little for sound blocking. Is this "massive" enough. There also a bezel he adds made of wood which I'm assuming is also 1-1/2" thick but he doesn't indicate that.
This guy's "massive" walls seem to be made out of FABRIC?!?! link here: http://www.johnlsayers.com/phpBB2/viewt ... &start=285


Im not saying all of these are right or the same concept but a lot of these builds, even ones that seem to have no budgetary constraint, confuse me when it comes to the soffit walls. I'm following everything - and then when it comes to the soffit I'm scratching my head like WHY?!?!

Just to be clear - I have no issues just following the Sayer's or Barefoot design completely, although I know my situation (every situation) is unique and needs fine tuning. But instead of just "doing" it - I'd much rather UNDERSTAND it!

- Mike

Stuart!!! Thanks a million. you've convinced me - I SHALL VENT!

Amazing, thanks again. I'll double check my weight loads, etc.. before I actually build but this is great info.

Sorbothane provide a calculator app for figuring that out, but you do need to understand how it works, and what the numbers mean.

Ok so I will definitely NOT being lining the box AND doing the pads (M-S-M-S-M),

Well, you can if you really want to, but it does have to be calculated with care, like any other 3-leaf system.

How does a speaker radiate sound 360 degrees? (see photo) please excuse my HORRIBLE quick sketch

A bit of both, actually! There will certainly be some very low frequency vibrations induced in the cabinet itself, simply due to the motion of the drivers. That's a fair amount of mass moving backwards and forwards, and Newton's laws talk all about action and reaction... if the driver shoves the cone forwards, then the cone shoves the driver backwards, and since one of them is attached to the box, then some of that energy is transmitted into the box. The moving parts of the cone only weigh a few grams, and the box weighs several kilograms, so the effect is not huge to start with, but at high power levels, yes, there is some radiation going on from the cabinet itself due to this. Also due to the massive pressure changes going in inside, which are attempting to make the entire cabinet "breathe" or "pump". Hence, the need for a massive, rigid surround, to minimize all of the above.

But most of the "backwards radiation" effect comes from edge diffraction, and the simple fact that, for wavelengths larger than the smallest dimensions of the box, the entire speaker acts as a point source anyway. The simple act of the cone pushing large volumes of air forwards and backwards induces the same motion in the surrounding air. Sort of. It's a bit more complex than that, but that gives you a neat mental picture of what is going on.

Another way to look at it is that each wave appears to emanate from the center of the cone and spread out as a sphere in all directions, for all wavelengths larger than the smallest dimension of the baffle. From that point of view, part of each wave appears to be spreading across the speaker baffle "sideways", starting in the middle and running outwards, across the face of the baffle. And when it reaches the edge of the baffle, due to the sudden change in impedance, the wave appears to "wrap around the side" of the speaker, and continue spreading out towards the back.

And a soffit mount deals with ALL of these issues! The "muddy" energy being radiated by the cabinet itself is firstly contained within the soffit by the enclosure box around the cabinet, and is also greatly damped by the resilient mount in the Barefeoot design, as well as being damped even more by the large quantities of porous absorption inside the box. Any residual energy is even further contained by the front baffle of the soffit: it can't get out that way at all. Secondly, the front baffle of the soffit prevents the motion of the cone from causing motion in the air to the sides of the speaker, for obvious reasons. Third, the wavefronts that appear to be expanding outwards across the front panel of the cabinet, never reach the "edge", because the front baffle of the soffit is a continuation of that, and the walls of the room are a continuation of the soffit: Those waves cannot "wrap around" behind any more, because there is no place that they can ever get "behind" any more. For the same reason, there is no edge diffraction: there is no edge!

This is the reason for the 6 dB bass boost that you get from soffit mounting: For all frequencies where the wavelength was shorter than the dimensions of the cabinet, half of the energy wrapped around behind and went backwards, while the other half went forwards. And since "half of the power" is the same as a 6 dB reduction in power, the manufacturer had to boost the bass power by 6 dB to balance the power levels again. With the soffit, that is no longer necessary, because ALL of the energy is now going forwards, at all frequencies. None of it is going backwards (except for the small amount from the actual cabinet vibration, which isn't very much).

I think the answer to this will help me understand HOW the sound field is restricted to 180 degrees through soffit mounting.

I hope so!

As far as the other designs - I was basically referring something like this:

I would not do the first one, for several reasons. Not a good design. The second one is much better.

there's loosely packed insulation behind the wall, sometime I see hanging bass traps there too.

Don't think of it as a wall. Yes, in reality it sort of is a wall, but as far as the speaker is concerned, it is an infinite baffle and an enclosure and a rigid / resilient mount. The area behind the speaker is normally divided into sections, as well: there's the main section, where the speaker itself is, then the bass trap section down below, and perhaps also another bass trap section up above.

I see hanging bass traps there too. Are these helping with the control rooms acoustics or are these helping damp down the sound emitting from the rear of the speaker?

Room acoustics. Technically, those are in the room corners, which is a real good place to put bass traps. There's a large opening at the bottom of the soffit baffle, into the room, so that the hangers are exposed to the room air.

This is why I really need help with my question regarding HOW a speaker emits sound. Does it come FROM the rear?

Not really: it wraps around from the front, mostly. There IS some emission from the rear, but very little. (Different for the case of rear-ported speakers, of course...).

Also I am not seeing the "massive" front wall. 5/8" plywood and timber finish?

An inch and a quarter of solid wood isn't massive enough? That's around 20 to 25kg/m2...

f the box that goes around the speaker (assume made of 5/8" plywood) does little to block sound (and is for mounting purposes mostly),

It is in direct contact with the speaker cabinet (in the Sayers design) so it transmits then energy quite efficiently... but there isn't much energy there! That is structure-borne energy, not air-borne energy. The front baffle is dealing with air-borne sound, not structure-borne sound.

I also understand that the acoustic hangers BELOW the shelf in Johns design ARE for the Control Room acoustics, its mostly the stuff above I'm wondering about.

The stuff inside the soffit itself (above the shelf) is mostly for damping of the sound inside the soffit cavity, some of which comes from the speaker vibrations, and some of which comes from it just being a tuned cavity. Think of it this way: the soffit is just a giant speaker cabinet, and like all speaker cabinets, it needs internal damping.

Although unfinished - you can see the speaker is almost already entirely flush with the front of the box meaning the Bezel - or "massive" front wall is only going to be millimeters thick.

Ummmm not really! That's an Adam A7, A7X, or A8X. Here's a view from a different angle...
There's at least an inch and a half there, from the point where the bevel ends on the speaker cabinet, to the front face. That's a lot of wood. Plus a few more mm probably: the top edge of the bevel seems to be sticking out a bit in that photo...

This guy used 2 layers of 3/4" MDF for the front walls - seems reasonable to me

Yep!

but It's also what I suggested making my speaker boxes out of which Stuart mentioned does very little for sound blocking.

I think you misunderstood what I said: I said the enclosure box around the speaker cabinet does very little to stop the sound wrapping around from the front to the back.... But that's NOT the same as what the front baffle of the soffit is doing. Very different things....

This guy's "massive" walls seem to be made out of FABRIC?!?!

Then it ain't a soffit!

Just to be clear - I have no issues just following the Sayer's or Barefoot design completely, although I know my situation (every situation) is unique and needs fine tuning. But instead of just "doing" it - I'd much rather UNDERSTAND it!

I can't take the credit for John's design! That's all his work. I have done soffits based on both John's philosophy, and also on Thomas's philosophy. Both work. Of course, I do add a bit of my own ingenuity in both cases....


- Stuart -

STUART!!!!! THANK YOU SO SO MUCH!!!

Amazing response - this has helped me immensely!!

Hopefully I'll have time to work on my sketchup model tonight and this weekend so I can move forward with a soffit design now that I have a better understanding of whats going on. I already have a few new questions formulating in my head but I just wanted to get this THANK YOU out there now since it may be a few days until I post a new sketch and new questions and pictures.

Construction update: I just made the decision to go with an "almost" completely flush header in the basement. Originally I had it planned as a 12" tall I-beam that is flush to the subfloor (would have protruded 4 inches down). Instead, I am going with an 8" tall I-Beam which will be flush with the subfloor AND the bottom of the existing floor joists.

I'll be sure to post pics of this too - I think I may have the temporary support walls built this week or next in preparation.

- Mike

That's what we are here fore!

- Stuart -

Hey Stuart (or anyone else if you can help)

I have one quick question:

Do you know if I would be able to use these Sorbothane Stud Mounts?
JPEG here in case the attachment doesn't work
Urei 813 = 176 lbs
(1) 4' x 8' x 3/4" MDF = 96 lbs
Based on the proposaed size of my MDF boxes - each layer is approx. 172.25 lbs)

Therefore Urei 813 + (1) Layer of MDF Box = 348.25 lbs/ea

If I was to use 2 layers of MDF box then approx = 520.5 lbs/ea

I think up to here my math is correct.

THEN

Using the Sorbothane Part number I selected - I chose to divide my combined weight (348 lbs) by the MIDDLE number in the RATED LOAD of the stud-mount (20-40 lbs). IS THIS RIGHT?!?! So 348 LBS/30 LBS

Based on that it looks like I'd need (11) pads if I go with one layer of MDF Box or (17) pads if I go with two layer MDF Box.
(again I'm not sure if this math is correct)

The reason I want to use these threaded stud mounts is to eliminate the need for a strap (like in barefoots design) or coupling to the front wall in close proximity to the speaker. I was hoping that by using these stud mounts - I could ensure that the MDF boxes don't "shimmy" out of place from vibrating over time - and also ensure that the boxes don't get knocked even by a 1/16" of an inch for any reason, ruining the decoupling from soffit face. I don't know if any of this logic is correct so please let me know.

Here a shot of the current soffit design I've been working on. I am stuck because I need to know the thickness of the pads to use. I plan on putting these stud-mount pads between the concrete stands and the MDF boxes. This way I could fasten them and prevent any horizonal movement (beyond the pads deflection) while still de-coupling.
1) Shown is (2) layers of MDF Box but I haven't decided on (2) or (1) yet. Any advice is appreciated. 2) Now the piece of 3/4" plywood that would be the "shelf" in Johns design (the piece that separates the top and bottom portion of the inner soffit) would NOT be touching the concrete stand. Again my thought on this is decoupling, although I do realize that the speaker is already decoupled from the concrete stand so maybe this is not necessary. I show a 1/16" gap between the wood and concrete. If this IS a good idea..then should I caulk or backer-rod this gap? 3) Air Vent for cooling is shown as approx. 3" dia. Let me know if I need to go bigger. Also I only show it on the bottom of the box - I know it needs it on top too.
4) How much airspace behind speaker inside the MDF Box? - Right now I have about 3 or 3-1/2"
5) I also show a 1/16" gap around the front plane of the soffit framing and the MDF box is flush with the framing. The speaker protrudes out of the box 1-1/2" to allow for 2 layers of 3/4" ply or MDF. This can be easily adjusted (in the design) depending on the materials used if someone has a better suggestion of what to make this "massive" front wall out of. This last shot is where the Sorbothane stud-mount Pads would go (in between MDF box and Conc stand). I couldnt figure out how to point out the area in Sketchup but hopefully you can see the gap wherer the pad would go. A few notes:
1) I know my MDF box is incomplete I left those 2 sides off so we can see inside.
2) Obviously the front wall material is also not shown as I haven't really decided what to use yet!!
3) Obviously the internal soffit framing is not complete either yet - kinda caught up at this point.

Hey wait a sec - that was NOT 1 quick question

one slight edit here - i attached another photo to clarify that the "shelf" is not sitting on the conc stand - some of the previous pics look that way. The stand actually sits up a bit higher that the height of the shelf - this pic is exaggerated but it clears that up: Am I on the right TRACK here?!?

another update I may as well include in this same post:
2 options for the soffit face wall.

OPTION 1 (smaller size soffit but flush with subwoofers): OPTION 2 (larger soffit face - creates strange "shelf" area above subwoofers, smaller area to mount a flatscreen TV.): Last question is regarding DOORS!! (I know that sort of came out of left field)

In Rod's book he details a SINGLE door that goes between both leaf walls. Instead of the typical double door (1-in each leaf) method. Is this ACCEPTABLE?!? Not a MAJOR issue - but if I can have 1 heavy duty door - it would allow me to put the entrance to the control room right at the bottom of the stairs and swing INTO the control room.

If 1 NEED a 2 door assembly - then I CANNOT have my entrance at the bottom of the stairs.

Ok so that last post was kind of all over the place, I'm going to try to simplify my main problems and questions:

1) Sorbothane stud-mounts (part no: 0510350-50-10). Are these ok to use under the speaker or speaker box?

2) Is a (2) door assembly REQUIRED through a 2 leaf wall system? Is the single heavy duty door detailed in Rod's book acceptable? What are the downsides if any?

3) Does the inner soffit "Shelf" (in my case not supporting anything, just separating the top and bottom halves of soffit) need to be de-coupled from the concrete stand?

4) Is a 3" dia. air vent opening sufficient in the speaker box? Is 3-1/2" open space in the rear of the box sufficient?

5) I am thinking of using (2) layers of 5/8" plywood for the inner soffit walls (shelf, bottom and side). This was just to roughly match the front soffit wall which I'm thinking will be (2) layers of 5/8" MDF or maybe (1) layer 5/8" MDF, (1) layer 3/8" MDF and then a 1/4" finish wood. The reasoning for "beefing" up the layers beyond John's design was because these speakers are just larger than most of the design's on here that I am basing this off. As a side note I realize there are a few 3-leaf situations going on here - and I don't know how the equation for a 3-leaf works out - but I'm assuming that increasing "d" (or the airspace) would also help lowering the res. freq. in that equation, just as it does in the 2-leaf equation. There seems to be a significant amount of airspace between the leaves. Is this correct?

6) This brings me to the next question regarding isolation. If I'm doing the math correctly then the weakest point should be where the air gap is 8" and between two NEW studio walls made of (2) layers 5/8" drywall. This works out to be about 49.6Hz I think. I tried messing around with the formula increasing the gap by an inch or two and also adding a layer of 3/8" plywood. Adding 1" air gap - while completely free - only brings me to about 47Hz. (2) layers of 3/8" plywood (1 on each leaf) - while losing about the same amount of space - and cost way more money - brings me to about 44.8Hz - not too shabby. Adding an inch air gap on top of that I'm down to 42.7Hz. If I calculate between a (2) layer 5/8" wall and a concrete wall (8" gap) which I DONT know the surface density of (I couldn't figure out how to get kg/m^3 to kg/m^2) - but I plugged in 72 kg/m^2 as a guess. This gave me 37Hz. I would assume that these areas would give better isolation. I am slightly confused however because I thought I remember reading that having the 2-leafs being different masses is bad. I know there is a 3-leaf situation going on as well between the 2-new leafs and the concrete wall - basically the area where the couch is shown. But again the airspace is very large there, and I don't know the formula.
So this question is 2 parts:
a) I know the system is only as good as the weakest point - BUT, is my isolation to OUTDOORS, going to be better than my isolation BETWEEN two new studio walls? Since all of the leaf(s) between the outdoors are around 37Hz, (except for the 3-leaf thing going on in the couch room) and between new walls it's 49.6Hz??
b) WOULD a layer of 3/8" plywood going down as the first layer - be sufficient enough support to use to fasten the subsequent layers of 5/8" drywall? I did this years ago in my current studio - used a layer of plywood first - making it very easy to attach layers afterwords (and basically anything on the walls afterwords for that matter) since everywhere is "screwable". However it was only (1) layer of 1/2" gypsum on top and I didn't know WHAT I was doing at the time. 7) In John design, an illustrated in this pic, there is an offset, approx. 3-1/2" deep, just BELOW the face of the soffit, where the soffit is offset and the plywood layers are on the INSIDE of the soffit. Would this cause a point of diffraction? I know he puts the rigid insulation there to treat reflections off the console, but is this the lesser of two evils? Would it be possible to keep the rigid flush face all the way down to 12" above finished floor? In the case that case you still want to treat console reflections, you could add rigid insulation to the face of that - although now it would not be flush. To me it seems that having a soft surface protruding is better than a 3-1/2" offset in the rigid face? See below for illustration.

Option #1 Johns basic design with offset rigid surface: Option # 2
Rigid surface is flush - console treatment protrudes out: #8 Lastly - just want an overall idea if this current soffit design is going ok. I tried to maximize the size of soffit face. I also remember reading that the speaker should not be dead-center of the soffit face, so I chose to extend the soffit only a certain amount. This reduces the size of the strange "shelf-thingy" created above the subwoofers, although it is still there somewhat.
- I AM wondering if I should box in around the top of the subwoofers or just leave it open to above and filled with insulation. The subs are not in there tightly at all, there's a few inches in between them and on the sides as well. Also not sure if this front section needs a massive wall at all - or should I just cover this section with fabric to leave it open to the room for bass trapping/treatment? No insulation is shown - or isolator pads yet since I'm not sure what to use. The RIGHT speaker and soffit is the one we are looking at, once I finalize that side I'll copy it over to the left - that is why the left side is incomplete.

slight bump - and i also got this from sorbothane

"Thank you for contacting Sorbothane and inquiring if our material is a good fit for your application. You can definitely use the mounts for an application like this. You will just want to make sure you use the appropriate number of them so that the load per isolator is within the load rating of the part."

here was my question to them (edit: missing from original post) - " Hi - I am contacting you in regards to using one of your products in a recording studio design. I am planning on using Sorbothane pads to decouple a speaker from a concrete stand. The speaker itself weighs 176 lbs. There may be an MDF box built around this speaker bringing the total weight op to 348 lbs. Another option is to have the box made with 2 layers of MDF bringing total weight of speaker and box up to 520 lbs. I was hoping to use the Sorbothane Stud-mount Part Number 0510350-50-10 in order to decouple the speaker box from the stand while still fastening it from horizontal movement. The whole assembly will be on a level surface (there is no forward "tilt" on the speaker box). Any help would be greatly appreciated."


SWEET!!!!! this is major!

Also - Stuart if you happen to be poking around, I have 2 specific questions regarding the ceiling beef up as I plan to procure materials soon:
1) styrofoam (or other closed cell foam) in between the new gypsum layer and the existing subfloor. if existing nails are protruding 3/8" - should i get EXACTLY 3/8" thick styrofoam? or should i get 1/2" styrofoam and plan to SQUEEZ it in? is this even possible? would this cause upward pressure on the subfloor?
2) the existing subfloor is like tongue and groove style - should i be caulking this? also should i be caulking where the subfloor rests on the floor joists?

1) styrofoam (or other closed cell foam) in between the new gypsum layer and the existing subfloor. if existing nails are protruding 3/8" - should i get EXACTLY 3/8" thick styrofoam? or should i get 1/2" styrofoam and plan to SQUEEZ it in? is this even possible? would this cause upward pressure on the subfloor?

You don't need to be extremely precise! It can be a bit thicker, if necessary. Don't try to "squeeze" it though! Just use whatever thickness makes the most sense.

2) the existing subfloor is like tongue and groove style - should i be caulking this? also should i be caulking where the subfloor rests on the floor joists?

Yes! The general rule is that if you see a crack, then seal it. If it looks like a crack, then seal it. If it might not be a crack but you aren't sure, then seal it. And if you are absolutely certain that it is NOT a crack, then seal it anyway, just in case. Good sealing is critical to good isolation. If air can get through, then so can sound.

- Stuart -

Stuart!

Thanks as always for the advice. Now I just need to research what type of caulk to use in this application.
I've narrowed my questions down to just 3.

1) I'm still trying to decide which soffit method to build, here are the 2 options:

2) As far as the Sorbothane - it looks like I even calculated how many pads to use correctly! These stud mounts will help alot with the design. I do however wonder if I need more pads toward the FRONT of the box since it will be overhanging the stand by a few inches, will this cause more weight to be resting on the front part of the stand? (as a side note these are going to be mounted level - no forward tilt).

3) Convective Cooling air path size - any recomendation on how large to make the air path? 3"dia? 5" dia.?

slight bump

and i'm also having a hard time finding which type of caulk to use for the ceiling beef-up?
Does it need to dry flexible or can it be something that dries hard in this application? Should I use stopgap?

do i use the same type of caulk for sealing the existing cracks AND on top of the backer rod?

Any help would be GREATLY appreciated as I'm almost ready to order all my materials for the ceiling beef-up.

EDIT/UPDATE: Looks like I will be going with the OSI SC-175 for the acoustic caulk to use for the ceiling "beef-up"

Having a little trouble with the foam (for beef-up).

I can find some 1/2" thick closed cell for relatively inexpensive. My trouble is with this is some of the existing nails hang down almost 1" - so I need to go with 1" thick foam. How difficult will it be to install the 2 layers of 1/2" foam overhead on the existing subfloor? Even 1 layer seems difficult. Would it be acceptable to glue or just place the foam on top of the Gyspum board - then just lift them up together? This method would make it more difficult to ensure there are no seams in the foam layer. But I also can figure out how I would hold the foam in place.

Also - should the foam span from JOIST to JOIST? or should I leave a slight gap (the same way that the Gyspum layer has) and fill it with backer rod?

- Mike

THE STEEL BEAM HAS BEEN DELIVERED!!!!!

That one guy with the ponytail looked EXACTLY like Steven Segal!! lol I'm just going to start telling people that Steven Segal installed my beam because I think it may have been him. I've honestly been very worried that the beam wouldn't fit into the basement - its 1800 lbs and 18'-0 long!!

Next the temporary walls go up. Bought a new chop saw too!! Wow things are finally happening!
I'll be sure to post photos of the progress. After this beam goes in - I going to start the beef up right away, but I still have a few material questions.

I purchased a 12-pack of SC125 (28 Oz. tubes) and an large caulking gun to begin sealing up the existing sub floor and for the beef-up. I'm sure I'll need way more caulking than that but its just the start.

Now the MAIN QUESTION I have is regarding the closed cell foam to use in between the subfloor and the new gypsum layer (I have the issue of the existing nails sticking down). Should I be using POLYSTYRENE (the lightweight rigid stuff that will make a mess when I cut it) OR should i be using POLYETHYLENE - the soft flexible stuff, comes in rolls?? There are obviously other types of closed cell foam like neoprene or elastomeric type stuff like is used in refrigerant piping insulation (armaflex) but I'm hoping I won't need that as I believe those are more expensive.

I also ordered (I know its WAAAYY EARLY) the Sorbothane pads for under the speaker boxes. I went with the Stud-Mount type and I ordered a few extra (42 in total) which was not cheap! They are sooo squishy!!

So on to the other less immediate questions:

1 - I think I am going with the SINGLE DOOR frame method through 2-LEAVES as detailed in Rod's book. I know this is counter-inuitive and Rod's book even makes note of that, but it also says - don't worry and just the build the frame straight through. So unless I'm making a huge mistake, I'd really prefer this method as opposed to two doors (1 in each leaf).


2 - Ventilation - Do I need a silencer box on BOTH inside inner leaf AND OUTSIDE the outer leaf? If I run the duct as shown once inside the inner leaf with the (3) 90 degree turns - and build a soffit around it - would that suffice as the inner leaf silencer. It's sort of like a stretched out silencer box no? See below from the sketch up (soffit not shown) Light grey duct is SUPPLY, dark grey duct is RETURN:

More on ventilation later but the duct sizing I have shown (10"x17") INCLUDES Lining THROUGHOUT. If I am going INTO a silencer box that is mounted on the OUTER leaf, do I even need to line the duct upstream of that (basically ALL of of that metal duct outside the control room)? This would help me immensely in reducing the duct size and loss of ceiling height.

Other than this question, I did most of the airflow calculations (as far as CFM, FPM, air changes, and duct sizing) but still need to do more research regarding friction loss, duct size changes, etc.. If possible I'd like to even further reduce the size of the ducts in those areas OUTSIDE of the control room which I know will make the velocity will go up, but I'm hoping that enough length of large duct downstream will bring the FPMs back down (in other words bottle-neck the duct slightly in the "Lounge" area). If anyone has suggestion that would be greatly appreciated. I plan to put (1) exhaust register in the bathroom, and install a vent in the door at the bottom. The supply grill will be in the lounge area. This way any air/smoking in the lounge area will get exhausted through the bathroom door vent, even if the door is closed.

3- Ceiling: In case anyone downloads the sketch up file there is a 3x3x1/2 angle iron shown as ceiling joist support. I'm not sure if that will hold I need to consult a structural engineer because the calculations are ridiculously hard. The reason for this, is that the new steel beam - although flush, still needs t be soffitted around because of the way I'm doing my ceiling. In order to maximize height, I am installing the new ceiling joist up in between the existing floor joists (I detailed this in an earlier post, but its also in Rods book). In order to do this, the new joists must run parallel to the existing floor joists, so 1 Side needs to be supported by the end wall framing and a beam spanning across. Maybe an I-Beam, hopefully a small heavy gauge 3x3 angle will be needed. The other option would be to do an inside out ceiling supported normally on the new wall frames on both sides, but the joists would be running perpendicular to the direction of the sound coming from the speakers. I'm not sure what John recommends but this would seem worse that having the beams run parallel to the sound waves, sort of like speed bumps?? Any suggestion?

Link to Sketchup File:

http://we.tl/pFoIg97F44

Any MAJOR Mistakes?!?!


I'm sure a lot of you have seen this Tom Hidley interview:

https://www.youtube.com/watch?v=ngHz3NfmnQU

I never realized this, but he designed the A room at this studio that I've worked at a handful of times called The Music Palace (which is mainly what he talks about in this interview). It's literally 10 minutes away from me. I always though it was one of the best sounding control rooms (and the LIVE room is equally if not more impressive) that I've actually been inside and listened to. And hearing that room is definitely a large part of the reason I am passionate about building my own amazing sounding studio. To just now find out that it was deigned by the great Tom Hidley is pretty crazy!

In this interview he keeps mentioning "diaphragmatic" absorbers or traps or membranes. Do you know if he is referring to hanging bass traps? The way he calls is "diaphragmatic" makes me think more of a sealed type of absorber?? Maybe I am thinking of "tympanic" instead of "diaphragmatic"? Would a hanging bass trap be thought of as a "diaphragmatic" absorber?

Just food for though not a real question.

- Mike