John Sayers' Recording Studio Design Forum Archive

slight bump!

How did you manage to keep the beam attached to the truck, with both of them hanging vertically like that?
That's a pretty amazing feat!

I'm just going to start telling people that Steven Segal installed my beam

Ahhh HA! So THAT'S how you did it! That makes sense. Either him or Chuck Norris. Nobody else can hold a truck on a vertical slope while hauling a beam up a vertical driveway and making it sit flat on a vertical slab....



Please fix your pictures so they are horizontal... it's hard to view them like that.... I don't plan to lie down on my desk so I can see your thread!

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??

It doesn't really matter that much. More mass (higher density) would help a little bit, but it probably isn't very relevant. The only real purpose of the foam is to keep the air out, so you don't have an air-filled cavity up there.

I also ordered (I know its WAAAYY EARLY) the Sorbothane pads for under the speaker boxes.

Yup, "early" is the word, for sure! How did you calculate the thickness, size, deflection and frequency for those pads, when you don't even have your final soffit design completed? Did you use the Sorbothane application for that, .... or did you just take a wild guess and hope for the best?

2 - Ventilation - Do I need a silencer box on BOTH inside inner leaf AND OUTSIDE the outer leaf?

How much isolation do you want?

If I run the duct as shown once inside the inner leaf with the (3) 90 degree turns

What size duct do you need to provide the correct flow volume for your room (cubic feet per minute, based on room volume and correct number of room changes per hour), at the correct flow velocity (feet per second), such that the air is moving slowly enough to not make a noise? What cross sectional area do you need to do that? Did you allow for the thickness of the interior duct liner when you calculated all of that? You DID calculate it, right?

Light grey duct is SUPPLY, dark grey duct is RETURN:

Those are on opposite sides of the back of the room: how do you plan to make the air move around the FRONT half of the room?

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

Not really, no. you can skip the liner on that part, assuming that it is all outside of the studio itself.

but still need to do more research regarding friction loss,

Hint: google "static pressure in HVAC systems". Happy reading!

duct size changes,

The cross sectional area needs to change suddenly by a factor of at least 2, in at least a couple of places. That creates a sudden impedance mismatch, which is a good thing.

This way any air/smoking in the lounge area will get exhausted through the bathroom

That probably is not permitted by code... Normally it is a big no-no to exhaust the stale air from one room into another room...

I'm not sure if that will hold I need to consult a structural engineer

Yep, you sure do! You need to consult him for your ENTIRE design, to make sure that it is safe, structurally, and meets your local building codes.

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?

Sound does not travel only outwards from the speakers in straight lines: there is also a reverberant field in the room, pus numerous reflections from all over. Sound will be somewhat randomly incident on the ceiling, to a certain extent, so the joists on an inside-out ceiling act something like diffusers.

Besides, you also need cross-bracing between your joists...

In this interview he keeps mentioning "diaphragmatic" absorbers or traps or membranes. Do you know if he is referring to hanging bass traps?

Nope! He is talking about diaphragmatic and membrane traps! very different from hangers. Membrane traps and diaphragmatic traps are tuned resonant devices with sealed air cavities inside. Hangers are not.

Would a hanging bass trap be thought of as a "diaphragmatic" absorber?

Nope.


- Stuart -

STUART! Thanks again for the response - always EXTREMELY APPRECIATED!!!!

How did you manage to keep the beam attached to the truck, with both of them hanging vertically like that?

hahaha - gravity is really strange in this town - its SIDEWAYS! Nothing Steven Segal can't handle though.

Sorry I couldn't figure out how to rotate the pics!! I'll attempt now.

It doesn't really matter that much. More mass (higher density) would help a little bit, but it probably isn't very relevant. The only real purpose of the foam is to keep the air out, so you don't have an air-filled cavity up there.

GREAT! thank you so much Stuart! Now i can get started with the BEEF UP!

Yup, "early" is the word, for sure! How did you calculate the thickness, size, deflection and frequency for those pads, when you don't even have your final soffit design completed? Did you use the Sorbothane application for that, .... or did you just take a wild guess and hope for the best?

I pretty much have my final soffit design complete. A few small questions remain but they are regarding the cooling vent hole size opening, which I don't think will affect the pads (making a bigger hole will reduce the weight slightly of the entire MDF speaker boxes, this will be calculated and if a pad needs to be removed, it will be done). I did use the Sorbothane app as well as talked to with one of their Engineers directly and detailed my exact application - they are the ones who recommended how many pads to use and confirmed that these pads were good fit for this application. I showed my calculation of a previous post but basically I calculated the weight of my speakers + speaker boxes so that each pad is holding (30lbs). The pads rated load (20-40 lbs) - this allows for some play as well. One thing I DIDN'T calculate is the deflection distance of the pads (once loaded). I'm hoping I can just adjust my soffit face-hole/opening lower the fraction of inch or however much they deflect. I was actually planning on doing this as a field measurement regardless once the speaker stands were installed and speaker mounted on top, just to make sure the soffit face is not touching all around.

I ordered (8) extra pads from what I calculated, so if I end up needed a few more I have them - a few less no problem.

The Sorbothane App tells me 94.28% isolation
with a natural freq of 13.31
I'm not sure if this is correct but the app looks for an input for the "excitation frequency" which I am not sure what that is. The speakers are crossed over @ 80Hz so I put 80Hz in. Is this right?!?!?

Speaker stands - calculated weight approx. 816 lbs
Surface density of speaker stand = 33kg/m^2???

Speakers + Speaker Boxes = 520 lbs
Surface density of speaker and speaker boxes = 27kg/m^2???

The speakers that are soffit/stand mounted are being crossed over @ 80Hz, so these boxes will not be getting the low-low end.

Mostly I went ahead with the purchase because of speaking with the Sorbothane engineer - and also your advice on needing several small pads at 50 duro (shore 00 scale).

But now since I am paranoid I did it wrong - I have actually just emailed them again with a sketch of the application as well as the concerns regarding 'excitation frequency' and 'natural frequency' as it applies to my situation since the original correspondence didn't have any mention of that and I'n not sure if I'm using the calculator app correctly.

How much isolation do you want?

Well - I calculated my weakest walls point at about 47Hz - so at least that I'm hoping?

What cross sectional area do you need to do that? Did you allow for the thickness of the interior duct liner when you calculated all of that?

Here's what I calculated:
Criteria:
8 air changes per hour
Under 300 FPM

Room Volume: 1764
Min CFM req. = 250 CFM
In order to maintain under 300 FPM - duct sized at 12 x 10 I.D. (using airspeed formula)
Duct shown on the drawings is 14 x 12 (added 2" for duct liner)

I plan on using 20-22 ga. galv sheet metal duct w/ 1" duct liner.

(This is all only for the control room at the moment) - AHU will be sized based on all rooms requirements - prob 500 cfm unit

Yes I still need to calc. the static pressure of the entire system and other things, but am I at least on the right track as far as duct sizing within the room??

Those are on opposite sides of the back of the room: how do you plan to make the air move around the FRONT half of the room?

I was actually assuming they SHOULD be on opposite sides of the room - if they were both on the same side the air would just short cycle and go from the supply right into the return.

Are you saying I should put more than one supply grill to spread the supply air? I have the grill facing the FRONT of the room. 300 FPM definitely does not THROW the air - but its doesn't exactly dribble out either - there is some speed to it. So I was hoping the front facing supply grill would shoot the air gently towards the speakers and then disperse throughout the room, then the return grill in the rear of the room would take the mixed around air. Are you saying that the air is just going to make a B-Line right from the supply grill to the return grill??!

Not really, no. you can skip the liner on that part, assuming that it is all outside of the studio itself.

Ok great, even saving 2" is amazing.

I also just realized that the AutoCAD MEP version I have for my dayjob can do all of the duct calculations for me - I just draw the duct and it shows me the friction loss!!! I'm still going to do my research but this is a good way to double check everything.

That probably is not permitted by code... Normally it is a big no-no to exhaust the stale air from one room into another room...

Ok - another grill isn't too big of a deal - thanks.

Besides, you also need cross-bracing between your joists...

Ah ok - I was thinking I'd still be able to do that like this:
But I see what your saying even in-side-out ceiling I will have joists running both ways essentially.

Stuart - did you get a chance to see my post where I decided to go with (1) Single door through 2-leaves as detailed in Rod's book? - I didn't see any scolding for that so I'm hoping it OK!!!!!??

I'm not sure if this is correct but the app looks for an input for the "excitation frequency" which I am not sure what that is. The speakers are crossed over @ 80Hz so I put 80Hz in. Is this right?!?!?

Nope!

80 Hz is the frequency where the cross-over STARTS to roll off the low end of the feed to the mains. What is the roll-off RATE? Assuming 12 dB per octave, and a level of 80 dB... at 40 Hz your mains are still putting out still have 68 dB, at 20 hz they are still putting out 54 dB... If the roll-off is 24 dB/octave, then you still 56 dB at 40 Hz.

I use the point where the output is about 15 dB down. I'd assume something like 35 Hz for the lowest excitation frequency. I'd hazard a guess and say that you won't be getting 92% isolation for that! And I doubt that it will be 13 Hz, either...

One thing I DIDN'T calculate is the deflection distance of the pads (once loaded)

Then I don't know how you came up with 92% and 13 Hz!!!! One of the necessary inputs to the Sorbothane app is the deflection.... If you didn't put that in there, then your results are invalid....

You should probably re-calculate, using the correct deflection, and the correct excitation frequency.

I'm hoping I can just adjust my soffit face-hole/opening lower the fraction of inch or however much they deflect.

That's not the main reason for calculating the deflection: The main reason is to ensure that the pads are compressed correctly. Too much deflection, and they "bottom out": no isolation at all. Too little deflection and the "top out": no isolation at all.

Surface density of speaker stand = 33kg/m^2???

How did you arrive at that???? You need to know the AREA of Sorbothane that will be supporting the weight of the speakers.

Speaker stands - calculated weight approx. 816 lbs

Why do you have the weight of the STANDS in there??? The stands are not resting on the sorbothane---- Only the speakers + enclosure boxes are resting on the sorbothane...

Speakers + Speaker Boxes = 520 lbs
Surface density of speaker and speaker boxes = 27kg/m^2???

So each speaker weighs about 80kg, and each box weighs about 155 kg? Those are MASSIVE speakers you have there... and massive boxes...

But assuming that is correct, you are saying that you will be resting your boxes on 114 cm2 of Sorbothane???? In other words, each speaker will be resting on a pad that is 10cm long by 11.4 cm wide? Roughly 4" by 4-1/2"? Is that correct?

Assuming the above is correct, and you have 1/2" 50 duro pads, with assumed 10% deflection, I'm getting a natural frequency of 41 Hz, so for an excitation frequency of 35 Hz the isolation will be -86%. Yes MINUS 86%. In other words, amplification, not isolation. At 80 Hz, you would get 29% isolation. However, the actual deflection would be only 7%, and since Sorbothane needs an optimal range of 15 to 25%, I'm not so sure that is going to work...

Either that, or something is wrong with your weights and areas and deflections...

are being crossed over @ 80Hz, so these boxes will not be getting the low-low end.

Yes they will. Cross-overs are not absolute vertical cliff cut-offs: They ROLL OFF the frequencies below that point at a certain rate, which might be anywhere from 3 dB/octave to 48 db/octave. 12 and 24 are common rates. So even though the roll-off starts at 80 Hz, or has it's -3dB point at 80 Hz, there is still substantial energy coming out of that thing for frequencies below that point, down for at least one octave, and likely two octaves.

as well as the concerns regarding 'excitation frequency' and 'natural frequency'

"natural frequency" is an assumption you make about what the natural resonant frequency of the system will be. You then refine it by repeatedly updating your "guess" and looking at the "natural frequency" calculation that the app gives you. If the number that it shows is within a couple of Hz of your guess, you are fine.

"excitation frequency" is the one you want to test for, after you get the above correct. Once you have all the input data correct, you can put any frequency you want into that box, and it will tell you how well the system will isolation for that frequency. Try several frequencies to get an idea of how the system will behave. If you want to get fancy, plot them on a graph.

How much isolation do you want?

Well - I calculated my weakest walls point at about 47Hz - so at least that I'm hoping?

Hz is frequency, not isolation! How much isolation (in decibels) do you want at 47 Hz? And why did you choose such a high frequency? don't you ever record / mix / listen to bass guitars, big kick drums, acoustic pianos, and the low end of electric guitars, and keyboards? They all go down into the mid 30's....

but am I at least on the right track as far as duct sizing within the room??

Looks good so far...

I was actually assuming they SHOULD be on opposite sides of the room - if they were both on the same side the air would just short cycle and go from the supply right into the return.

... unless, of course, you put two supply registers at the back on the ceiling, spread apart aiming outwards, and two return registers at the front, on the ceiling, spread apart, roughly over the speakers, where they will pick up all the warm air from your gear, speakers, and people....

Are you saying I should put more than one supply grill to spread the supply air?

If you want to get your register speed down to 100 fpm or so, then that's the only realistic way of doing it....

So I was hoping the front facing supply grill would shoot the air gently towards the speakers and then disperse throughout the room, then the return grill in the rear of the room would take the mixed around air. Are you saying that the air is just going to make a B-Line right from the supply grill to the return grill??!

Room symmetry? Symmetrical air movement? OK, so air movement is not a huge deal for a home studio, but symmetrical air movement could be important in a mastering room. Might as well copy the "best practices" from the big boys, to get your room as good as it possibly can be. If you do 20 things that each make a tiny, almost imperceptible difference to your room, the result is a BIG difference.

Ah ok - I was thinking I'd still be able to do that like this:

I doubt that would fly: Ask your inspector if he would approve that... He MIGHT, but I'm betting he wouldn't.

But I see what your saying even in-side-out ceiling I will have joists running both ways essentially.

Yep!

Stuart - did you get a chance to see my post where I decided to go with (1) Single door through 2-leaves as detailed in Rod's book? - I didn't see any scolding for that so I'm hoping it OK!!!!!??

That sort of leads back to ... "How much isolation do you need?" And also: "If you do 20 things that each make a tiny, almost imperceptible difference to your room, the result is a BIG difference."

If you don't need too much isolation, then build a single Rod Superdoor (and get several strong men to help you lift it into place... ): If you need lots, then go with a pair of back-to-back doors.

Now, maybe I'm just too much of a perfectionist.... But that's me! Your mileage may vary. Void where prohibited by law. Rinse: Repeat. (And all those other snazzy marketing phrases too!)


- Stuart -

Hey Stuart -

So my calculation regarding the speaker resonant frequency (while non-existent) - also show that I am not even close to being on the right path!!!!!!!

So all I calculated was the weight of the speakers + boxes, then divided by the bottom area:
Giving me the surface density of the speaker box??

I also thought I would need the surface density of the speaker stands since I have heard on here before that the speaker stands should be more massive than the speakers in order to lower the resonant freq.

I thought I needed both of these - and then using the MSM formula to calculate the resonant freq. of the system....so basically WAAAYY OFF

I did nothing with calculating the surface density of the pads themselves

And yes they are very heavy the Urei 813 box with speakers baskets IN - is 176 lbs. Add 2 layers of 3/4" MDF and it goes up to 520 lbs. I guess the speakers are probably made of something close in weight to 3/4" MDF since (1) box of MDF is roughly 170 lbs.

Here is the correspondence I had with Sorbothane:

ME: Hi - I am contacting you in regards to using one of your product 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.

THEM:
Dear Michael,
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.
Since we only sell these parts direct in bulk quantities, I have included a link below to a page on our site that lists some of our distributors. If you have any other questions or concerns, please let me know. Thank you very much.

ME: Thank you so much for the response.
I had calculated how many pads to use, using the following method.
Pads "Rated Load" at 20-40 lbs
Total weight of speaker and box 348 lbs.
In order to be safely within the pads rated load I chose 30 lbs.
348lbs/30lbs = 11 Pads
Is this correct?

(NOTE: THIS IS HEN I WAS PLANNING ON 1 LAYER OF MDF - HENCE 348 lbs)

THEM: Michael,
That would be correct if there was a specific pad you had in mind to use. The other approach would be to divide by the number of pads you want to use, say 4 which would be 348/4 = 87 lb/pad, then look at parts where 87 lbs fits the load rating. Either way will work. If you have any other questions or concerns, please let me know. Thank you very much.
Sincerely,
Robert


ME (TODAY): Robert,
Thanks again for responding. I actually went ahead and purchased the Sorbothane Stud Mount Pads based on our conversation.
I am on this recording studio design forum and based on the info I got here - I feel like I may have missed some details in my Sorbothane Pad selection.
I was hoping you could tell me if the application is correct.
I have large speakers mounted rigidly in boxes made of 3/4" MDF. The total weight of the Speaker + the box is 520 lbs. (see attached photo)
This box is then sitting on top of a solid concrete speaker stand, estimated weight approx 817 lbs - which is installed directly on concrete slab.
The Sorbothane Pads would sit in between the concrete speaker stand and the MDF speaker boxes.
Using the "Rated Load" of the Sorborthane Stud Mounts (20-40) I did 520lbs/30lbs = 17.3. I chose to put 17 pads underneath each speaker.
The website I am on mentioned I should be taking into consideration the "FREQUENCY" of the pads. - Which I did NOT do.
The speakers themselves will only produce frequencies above approx 80HZ (as there is an electronic crossover which only allows the speaker to receive roughly 80Hz and above)
Other things I didn't look at were size and deflection of the pads (the size of the pads I selected was just practical for installation)
Deflection I am assuming is how much the pads will move (a few millimeters) once the weight is sitting on top. I am not too worried about that. Is there anything I need to know about the deflection?
My apologies if this email is too much, I was just hoping to make sure I use the product properly to get the best results.
Part number for the Stud Mounts is 0510350-50-10

THEM: Michael,
At 80 hz you should not have to worry too much about the natural frequency of the parts. They should be fine.
For deflection, unless you are noticing splitting in the material from compression. I would not worry about the deflection either. If you have any other questions or concerns, please let me know. Thank you very much.
Sincerely,
Robert


The pads I ordered are cylindrical shaped - diameter 1.75 inches - and thickness .85 inches. They are called "Stud-Mounts" since they have threads on both ends (only to be used in compression - not hanging things from it) I am planning on putting 17 underneath each of the boxes.


Ok so more thought has to go into the ventilation as well - I never even tHOUGHT of airflow symmetry being an issue!!! Thnks again for all the insight stuart - at least at this point all i may wasted was a little money (hopefully not) on the wrong pads.

As least i didnt install the damn things incorrectly!

EDIT: Sorry for this rushed and mangled - response I actually have a session that just - but I need to rethink the walls as well and isolation. The door thing I think would cause so many other design problems that I may just stick with the one. Anyway, thank you from steering me away from DOOM again Stuart

Giving me the surface density of the speaker box??

But that's no use: you want the surface area OF THE SORBOTHANE! The only thing that matters is the sorbothane: How much are you loading it? If you have one square inch of sorbothane supporting your speaker, and the speaker weighs 50 pounds, then the load on the sorbothane is 50 lbs/in2. If you use a pad twice as big, then the load is 25 lbs/in2. If you use a pad half as big, the load is 100 lbs/in2. The surface area of the speaker box is irrelevant, since most of it is not touching anything: it's only he area of the rubber itself that is supporting the weight.

I also thought I would need the surface density of the speaker stands since I have heard on here before that the speaker stands should be more massive than the speakers in order to lower the resonant freq.

Well they DO need to be massive, yes. That's correct. But they are not resting on top o the sorbothane, so their weight is irrelevant.

Sorbothane is basically a spring, and is subject to the same spring equations are any other spring. You have a load on it, and that load causes deflection of the spring. That deflection could be either an extension or compression, depending on if the load is hanging below the spring or sitting on top of it. In the case of a speaker sitting on a sorbothane pad, the load is on top of the spring. It causes deflection in the rubber: If it started out one inch thick, for example, then after the load is put on top it would end up as 13/16" thick, for example, which would be a nice 19% deflection. The rubber does not "compress": it "deflects": The top squishes down, yes, but the sides squish out. depending on the shape of the rubber pad, the same amount of weight on the same surface area might cause different deflections. A round pad and a square pad would act differently, with different deflections, even though they both have the same surface area and the same load on top. A ring-shaped pad (hole in the middle) would act differently again. This called "shape factor", so you also need to take that into account when you calculate. You need to tell the app what shape your pads are.

I thought I needed both of these -

The ONLY weight you need to take into account, is that which is actually resting on the pads. That would be the weight of the speakers themselves, plus the weight of the enclosure boxes if you do it the way you are showing in your images. But that's not the way I do it...

and then using the MSM formula to calculate the resonant freq. of the system

Nope. You need to use the app that Sorbothane provides. Rubber is not like air. Air is compressible. Rubber is not. There is no shape factor for air: there is for rubber.

I did nothing with calculating the surface density of the pads themselves

... and you don't need to! Maybe you are confusing the term? Surface density refers to the amount of mass behind a surface, such as the surface density of a wall, which tells you how much each square foot of the wall weighs. You don't need to know how much each square inch of sorbothane weighs! What you DO need to know is the pressure that the speaker applies to the sorbothane. It is measured on the same units, but it is a different thing.

in order to decouple the speaker box from the stand while still fastening it from horizontal movement.

... How do you intend to accomplish that?

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.

Yep!

The pads I ordered are cylindrical shaped - diameter 1.75 inches - and thickness .85 inches. They are called "Stud-Mounts" since they have threads on both ends (only to be used in compression - not hanging things from it) I am planning on putting 17 underneath each of the boxes.

As luck would have it, that actually works out! you would get 22% deflection like that, the natural frequency would be about 15 Hz, so for an excitation of 35 Hz you would get 60% isolation, which isn't bad. You could down to 16 pads for slightly better performance, or up to 18 pads for slightly better deflection (about 21%), but you are in the ball park.

I'm assuming that those really are 50 duro pads?

So it looks like you are OK there... but more from luck than from calculation!

I never even tHOUGHT of airflow symmetry being an issue!!! Thnks again for all the insight stuart - at least at this point all i may wasted was a little money (hopefully not) on the wrong pads.

It can be... if you are a perfectionist! Some people like to take the back panel and amp off the rear of their speakers and mount it on the soffit, for easy access to the controls... and that's fine... just don't mount it directly under your speakers, as the hot air rising from the amp between you and the speaker can cause tiny variations in the sound transmission between the speakers and your ears, sort of like "heat haze" can distort your view of the road on a hot day... If you happen to be concerned about minuscule effects like that, ...

The door thing I think would cause so many other design problems that I may just stick with the one.

Have you considered using sliding glass doors? Or moving your door if there is an issue with the sweep path?

Anyway, thank you from steering me away from DOOM again Stuart

Well, we figured out the VERTICAL loading and isoaltion of your speakers, but you still need to get to the HORIZONTAL part... how are you going to stop it vibrating sideways, if you hold it in place rigidly? (I know how I do that, but let's see if you can figure it out... )


- Stuart -

Stuart - thanks again for the ultra-informative response

So the crossover I have is 24dB/Octave (Marchand XM9)

So I plugged in 55Hz (roughly 15dB down point) to the Sorbothane app:

Natural Freq = 14.57
Percent Isolation 86.66%

There was only the option to put in 20% assumed deflection (not 22%).

And yes the pads are Duro 50, here's the info:

Part No: 0510350-50-10
Style: M-M
Thread: ¼-20
Dim A (Diameter): 1.75
Dim B (Thickness): 0.85
Dim C (Thread Length): 0.50
Duro: 50
Rated Load: 20-40 lbs


Since we are on the pads discussion, heres my plan for HORIZONTAL movement:

Here is the pad I purchased:
I order to hold the speakers in place horizontally, I was planning on doing the following:

Step 1 - FASTEN PADS TO CONCRETE STAND. to accomplish this - I could set the pads in the concrete that will be poured into the speaker stand (CMU blocks have that hole in the center, the hollow part, I was planning on filling this with SOMETHING - sand or concrete) and letting them dry in place with the concrete. Another option would be once the concrete is poured, then drill holes for expansion anchors or possibly just 1/4" by 1/2" deep holes and put some epoxy or some sort of glue on the thread, stick it in the hole, and let it dry. as a 3rd option, I could just fill the concrete stand with SAND, and then only mount the pads where the mortar joints are in the stand. (I believe the CMU blocks chip if you try to drill into them and you can only drill into the mortar part...is this correct?) - either way - FASTEN THESE SUCKERS DOWN.
Step 2 - DRILL 17 HOLES IN BOTTOM OF MDF BOX - before assembling the MDF Speaker Boxes, I would make a template of the pads layout which are now fastened to the stands. Using this template, I would drill out 17 holes in the bottom panel of the soon-to-be MDF box. Holes Dimensions: 1/4" (or slightly larger than thread size) x 1/2" deep - actually slightly deeper to ensure that no weight sits on the thread itself, only on the pads surface. I would test fit this panel on the pads threads to make sure it fits before assembling the box. Keep in mind the box has 2 layers of MDF so any structural weakness or thin areas of MDF where the holes are drilled, will be backed by another layer of MDF.

Step 3 - Assemble box around the speaker - then - Get a few guys to help me hoist up the completed speaker-in-box-assembly, with the pre-drilled holes on the bottom, and carefully drop into place. As long as the pads are held firmly in the stand, there shouldn't be any problem with a pads moving out of place. I honestly don't even think I would need any glue or anything to hold the speaker once it fits into those holes (maybe some acoustic caulk that dries soft in case anything gets loose).
So my hope in this design is that the weight of the speaker box (520lbs) is really working with me as part of the design. Basically the heavy weight would act like the strap around the speaker box in Barefoot soffit design - holding it in place. Once the threads are nestled into those 17 holes, the speaker should not be able move in any horizontal direction (front, back, left, right). Now of course if you KNOCKED INTO the speaker during the build process, it could potentially get TIPPED OVER. But its 520 lbs - you have to fall into it really hard. I could always put in some temporary bracing if necessary. Then once the soffits are complete, the only horizontal forces on the speaker I would have to worry about would be during playback from the actual speaker cones producing sound or vibrating. This should be minimal, and I don't see any way the speaker could "walk" off of those 17 pads with the threads embedded 1/2" in the base.

Anyway this was my plan and hopefully this is all somewhat reasonable and I am not missing something MAJOR! (I wouldn't be surprised).....


Ventilation:

Return - I really like your ideas for having the return up front so I switched things around. I may need to "pancake" the duct quite a bit, but I have some room to squeeze in a vent overhead and added 2 return grills up front. This also forced me to think about the ceiling cloud since they will be in the same area - so I sketched up a VERY TEMPORARY ceiling cloud. Once I added the cloud - even with only a 5% angle, the front part of the cloud was encroaching on the top speaker cone. Not exactly blocking it but too close for comfort. So I had to lower the speaker 2" and all of the framing and and soffit face along with it.

Supply - The supply duct was easy. Now the light grey duct is the return and the dark grey is the supply.
I was still wondering if there is any loss associated with building the "stretched-out" silencer boxes. In other words, instead of an actual silencer box mounted right on the inner-leaf wall opening, have the LINED duct run across the room as shown, but then a soffit built around it (maybe out of plywood like the silencer boxes, or 2 layers gypsum) maybe filled with insulation between the gypsum and the duct? Something like this:
or this:
If there were the same amount of turns in the duct that would be in the box, is it any less effective this way? I COULD put a box in the inside, but I'd RATHER use the space for bass trapping.


Door:

Yes I have tried painstakingly to make the (2) door method work. There is actually some room to move the door towards the REAR of the control room - however, it creates almost a WALL as you come down the stairs. I have a feeling this would be against code. I'm not even sure a door at the bottom is per-code, but at least I have seen that in several people homes so I assumed it would be.
It also would be fairly close to the back of the room -where I have my bass-trap framing shown currently.

(2) Sliding glass doors is a possibility I suppose, but this would also take up that same wall space. Also, it would be difficult to even out the left side of the room to maintain symmetry? Glass to nowhere? Hard surface? I must say though I LOVE the look of sliding glass. Possibly the door to the Live Room....

I also tried for a while to flip the whole room 180 degrees but it makes the door situation even worse if not completely impossible.

I CAN make the entry to the LIVE room a (2) door assembly. I'm assuming it would be better for overall isolation to have 1 'superdoor' (control room) and one DOUBLE door (live room) - rather than using two "superdoors"?? Any advice?


ISOLATION:

Ok so my isolation - I guess I'm sort of off the mark for this as well. So once I use the MSM formula for resonant freq. of a wall cavity....what do I do with that number? I have to admit I sort of lost the logic at this point. I do understand (only from reading through your responses to other peoples posts, Stuart), that you get good isolation 1.4 times above that frequency. I also know (from reading you responses again) that AT that freq, you can get bad isolation or even the opposite of isolation (boost).

I wan't good isolation, however, I don't know how to put that into decibels. (Please don't hit me with the Toy Drumset photo Stuart....)

And I DO realize that my 18" subwoofers that are crossed over at 80Hz WILL BE producing frequencies AT or well BELOW 47Hz, and LOUDLY....(by loudly I mean these are not NS-10 that roll of) they will be PRODUCING 30Hz... SO - I KNOW I need to isolate well at those frequencies.

A much as I plugged away at that formula, No matter what (within reason) I couldn't get the freq. down below say...40Hz. I tried with 9" air gap, 10" air gap. Adding a layer of 1/2" plywood to the (2) layers gypsum... so on. Even between my concrete walls and the new gypsum walls, the best I got was 37Hz.. Good isolation @ 1.4 times that is still only 51.8Hz. So bad isolation or possibly boosted below that??

So am I doing that math all wrong or am I not understanding the whole concept here. I know I cant be TOO TOO far off (am i?) since it seems to be a common method to build walls with (2) layers of 5/8" gypsum and an 8" air gap. MSM formula gave me, 49Hz. So this only yields good isolation above 68Hz?

As far as numbers . I would LOVE to be able to play music at 85Db (maybe even 90dB) in the control room, with the subwoofers on, and have my sister on the floor above to hear 30-35dB. Hopefully this is somewhat practical. I am NOT expecting to be able to play with the band with a drumset and bass amp (above 115dB) while she is sleeping.

EDIT: Last question about isolation removed due to it being a stupid question.

- Mike

slight bump!

Small Update!

Temporary walls going in for the column removal and beam replacement.
Question - if the floor is not 100% level, do I need to fix this? (also i am not sure yet if it is the floor slab or the ceiling joists that are not level)


Also I edited my last post to remove a question that I thought through and realized It was a bad question.

Also - heres a quick updated sketch:
- Mike

Slight Bump!

Aaaaaand...I'm about to pull the trigger and purchase some close cell foam for my ceiling beef-up.

I'm going with the Polyethylene. There are some options as far as DENSITY. 1.2 LBS all the way to 4 LBS. The price difference is extremely significant.

Before I go wasting money on the cheapest foam (1.2 LBS) - does anyone have any suggestions? on what is best?

I'm sure I'm not the only one who has done a ceiling beef-up and had the issue of nails sticking down through the subfloor, so any advice from anyone would be extremely appreciated.

here's a link to the foam i was thinking about

http://www.usafoam.com/closedcellfoam/polyethylene.html

So, I guess Stuart sort of answered my closed cell foam question earlier.....or did he?!?!

It doesn't really matter that much. More mass (higher density) would help a little bit, but it probably isn't very relevant. The only real purpose of the foam is to keep the air out, so you don't have an air-filled cavity up there.

How much is "that much"?

Based on this I'm about to go ahead and pull the trigger on the 2.2LB density foam!!!

However, I guess I'll always be wondering HOW MUCH the higher density stuff would help?

The price difference is pretty significant between 2.2 LBS and 4LBS. The pricing works out like this for the area of beef-up I need:

1.2 LBS Density = $592.00
2.2LB Density = $677.00
4 LB Density = $1,555.84

any suggestions?? almost 20,000 users I cant be the only one who has done a beef-up!!

I don't want to cut any corners financially on isolation - but if the extra $800-900 for 4LB density isn't going to make any real recognizable difference, well then its just not worth it.

slight bump!

among many other questions, I am mostly wondering if I am on the right track with my speaker stand isolation - I detailed my plan for horizontal movement in a previous post.

also wondering how to figure out the isolation between walls once I calculate the resonant freq...

slight (desperate) bump!!!

apologies in advance if I am doing something wrong to get some responses on my post - but slight bump again??

doesn't have to be Stuart that responds either (although I ALWAYS appreciate the expertise)

Sorry man! I got a lot on my plate right now, with several projects for paying customers doing various things, so very little time for the forum at present. I guess I missed your cries for help!

- Your speaker plan looks like it should work, but do make sure that you get the correct deflection once you have it all mounted. And make sure that no part of the "floated" section can touch anything else: not the front baffle,or framing, or anything.

Ventilation:

I would try to get as much of your ducting as possible outside of the room...

So I had to lower the speaker 2"

Careful there! You do not want the speaker too low! That's a recipe for disaster. The lower it goes, the more artifacts you will get from your desk / console surface, and the more off-axis you will be form the tweeters, and the more "blocked" will be the line of sight to the woofers. The speakers should always be set up such that the height of the acoustic axis is 120 cm (47-1/4") above the floor, or a bit higher, but never lower. If that interferes with your cloud, then modify the cloud. Bot do not modify the speaker geometry!

I was still wondering if there is any loss associated with building the "stretched-out" silencer boxes. In other words, instead of an actual silencer box mounted right on the inner-leaf wall opening, have the LINED duct run across the room as shown, but then a soffit built around it (maybe out of plywood like the silencer boxes, or 2 layers gypsum) maybe filled with insulation between the gypsum and the duct? Something like this:

You could do that, yes... but the duct needs to be large (internal cross section) to keep the flow speed down and reduce the static pressure.

Yes I have tried painstakingly to make the (2) door method work.

If there's no other way, then go with a single door, but make it as per Rod's "Superdoor". That's a big job to make that, and not cheap, but it's an excellent solution where there's no space for back-to-back doors.

So once I use the MSM formula for resonant freq. of a wall cavity....what do I do with that number?

You use it to figure out the isolation in each of the "regions" of the spectrum, like this:
f0 is your MSM resonant frequency, and f1 = 55/d

At the bottom end it is pure mass law, and above the top one is coincidence, but you don't need to worry too much about that.

That puts you in the ball-park, but isn't the entire story. If you want more accuracy, look for a paper titled "Accuracy of Prediction Methods for Sound Transmission Loss" by K. O. Ballagh. He goes into all the factors in more detail.

A much as I plugged away at that formula, No matter what (within reason) I couldn't get the freq. down below say...40Hz.

Are you SURE you are using it correctly? Two layers of 5/8" drywall on each side of a ten inch air gap should be giving you F0=10.87 Hz, isolation starts at 22 Hz and good isolation above 32 Hz... With damping, that becomes 8 Hz, 16Hz and 23 Hz... And that's just for drywall! With concrete for one leaf, you should be able to do even better...

As far as numbers . I would LOVE to be able to play music at 85Db (maybe even 90dB) in the control room, with the subwoofers on, and have my sister on the floor above to hear 30-35dB.

Very do-able... that should not be a problem.

Question - if the floor is not 100% level, do I need to fix this?

Probably a good idea... make it easier to build. Use self-leveling cement.

I don't want to cut any corners financially on isolation - but if the extra $800-900 for 4LB density isn't going to make any real recognizable difference, well then its just not worth it.

Adding mass is always good, and 4 PSF is a lot of mass. If you can do that (structural, not just budget!), then go for it. However, then light weight stuff would also work just fine, if you want to save money. Some people even use plain old styrofoam, which is dirt cheap.

- Stuart -