Groundlift Research & Development NEW STUDIO (consolidated)

doing some math on the HVAC system, wondering if you guys could have a quick look over my numbers, to see if I'm on the right track? (this is for the proposed control room) Size: 20x30x11.5 Volume: 6900 cubic ft x6 changes per hr: 41400 cubic ft divide by 60 mins: 690 (cfm?) according to my online duct calculator, given the target would be 300 fpm at registers, the ductwork inside the control room would need to be somewhere close to 20.5 in diameter, for a round duct, and 10x30 for rectangular ducts. this sounds pretty substantial for a 20x30 room. is this correct? (not sure i've ever even seen a 20" round duct, in person :P ) or... would this be split before entering the control room? and that then bringing the total number of silencers to 8, for a single room?? ps (edit) - actually, just got out my measuring tape and looked around the room a bit... 20" in diameter, for a single duct, doesn't actually look crazy.. it just sounds kinda outrageous on paper.. so maybe a single 20" supply wouldn't be quite as Hindenburg looking as i was afraid it would be :-) or, maybe a single 10x30 duct down the middle - or halfway - would look pretty ok as well.

Your 690 CFM checks out with me. Here's your duct sizing (see bottom of pic)These are all common residential duct sizes. But, your silencer boxes will be HUGE. You might be better off having two supply lines at half that CFM - Closest leaning to larger would be 400CFM. For air velocity of 300 ft/min, I calculate: 690CMF / 300ft per min = 2.3 square feet 2.3 square feet x 144 = 331 square inches. That's huge. That works out to about an 18 1/4" x 18 1/4" interior dimension for your silencer boxes. So, again, splitting that in 2 or even 4 would be awesome. It seems like your math is good. And yes, every duct would need a silencer on it. So, 1 supply and return would be your typical 4 silencer build. 2 supplies and returns = 8 silencers. 3 = 12 silencers, 4 = 16 silencers. Personally, since my builder screwed me over in at least one of my rooms, I have a small room (200CFM) where I'm going to have to build 3 supply lines (6 silencers) so that I can get the air velocity slow enough through my ceiling joists (luckily they used 14" deep I-Joists). Brutal, but do it right or don't do it at all. Greg

For air velocity of 300 ft/min, I calculate: 690CMF / 300ft per min = 2.3 square feet 2.3 square feet x 144 = 331 square inches. That's huge. That works out to about an 18 1/4" x 18 1/4" interior dimension for your silencer boxes.

There seems to be some big confusion here: You do NOT need such low flow velocities inside the silencers: the oft-quoted 300 fpm figure is for the air velocity at the REGISTERS, not inside the duct-work. The velocity can be much greater inside the ducts and silencers, as long as there's a decently long section where it has already been slowed down just prior to the register. And especially on the part outside the outer leaf: the velocity out there really doesn't matter at all, as far as the studio is concerned (although it might matter for the neighbors...) - Stuart -

howiedrum wrote:

not yet, but I'll let you know if anything develops!

Thank you. I met with the HVAC local guy that my contractor recommended and he was clueless. To his credit he didn't try to sell me on anything and said he would bid the job as I wanted to do it but he wasn't much help. He had never heard of NC ratings. Gasp! So I am back to the drawing board.

Howie As Stuart pointed out, earlier in this thread, most HVAC guys will not know the first thing about studio HVAC design. The key to your (our) success would be - as he said - to do the calculations ourselves (it's not very complicated once you sit down and make a list of all the cfm's, mph, fpm's, cuf's, abc's and lmnop's) and then have the builders install / build to your (our) specs, right Stuart? Once i sat down and wrote a few things down on paper, and plugged in the numbers, it's not crazy complicated - i think. I reckon the hardest part (which may actually have lucked out with) is finding a guy or gal that actually gives a damn enough to listen to you and then really do what is asked. Keep us posted!!!

There seems to be some big confusion here: You do NOT need such low flow velocities inside the silencers: the oft-quoted 300 fpm figure is for the air velocity at the REGISTERS, not inside the duct-work.

This is good stuff, Stuart! Thanks for chiming in. So, that begs the question: with 4 (for example) registers in a control room, roughly 20x30, would it make sense to have the same size ductwork (or close to it) feeding four legs of supply? And thus acheive enough of a 'slow down' that way? In other words: if i feed the room with a single 18" supply (hypothetically) and split it off to 2 or 4 registers (like an ... ehm .. octupus with 4 legs, y'know) and kept each leg the same diameter, that would be smart? The typical design, residentially and commercially, it seems (logically) would the the "big supply getting smaller and smaller" type deal, as airspeed is not an issue. Thoughs? Am i close? :D

So, that begs the question: with 4 (for example) registers in a control room, roughly 20x30, would it make sense to have the same size ductwork (or close to it) feeding four legs of supply? And thus acheive enough of a 'slow down' that way?

Think of it this way: there is a direct, unbreakable relationship between the air flow velocity, the air flow rate, and the duct cross section. Since the AHU fan will be moving air at a fixed RATE and VELOCITY as it comes out of the unit, you can control the VELOCITY in the rest of the system ONLY by varying the cross sectional area of the duct. If you increase the cross-sectional area, then the VELOCITY goes down, but the RATE stays the same. If you decrease the cross sectional area, then the velocity goes up, but the rate stays the same. However, decreasing the cross-sectional area also decreases the AIR PRESSURE (Bournelli's theorum), but increases the STATIC pressure, and considering that your AHU will have certain limits on how much pressure it can handle, you do have to be careful (just making the duct longer also increases the pressure, even if there is no change in cross-sectional area). Think of it like water flowing through your garden hose pipe: It is moving at a constant rate. If you put your thumb part way across the end of the hose, then that changes the pressure and velocity, but not the rate. To increase the rate, you have to turn the tap on harder. So there's this relationship between velocity, rate, pressure, and cross-sectional area. To be more precise, the TOTAL energy in the moving air is the sum of the KINETIC energy and the POTENTIAL, and it is fixed: you cannot increase or decrease the total energy of the moving air, except by adjusting the AHU controls. If the kinetic energy goes up at some point in the the system, then the potential energy MUST go down, such that the total stays the same. And vice-versa: if the potential energy goes up, then the kinetic energy goes down by the same amount. If this were not true, then airplanes and birds would not be able to fly. Therefore, changing the cross-sectional area at various points throughout the system is the ONLY parameter that you have control over in the design. Since you can easily check the manufacture's specifications for the AHU to find out what air flow rates and air flow velocity it produces at various settings, you can easily determine what the total cross sectional area is that you will need at your register, in order to ensure that the velocity NEVER goes over 300 FPM, even when the AHU is running at the highest setting. So that's your starting point: You will do the math, and figure out that you need "X" square inches of cross sectional area at your register. Now go to your local HVAC supply store, and look at registers: If the ones you are looking at that have the correct area just seem to be too big for your room, then you will probably have to split the air-stream at some point and use two smaller registers, that STILL ADD UP TO THE THE SAME TOTAL AREA. And if those smaller ones still seem too big, then you will need to split the airflow again, into FOUR registers, once again where the individual areas of those sum to the correct total area. There's another factor to take into account here: "open area". Registers have frames around them, and vanes on them that direct the air flow into the room. Those block some of the total surface area. So for example a 10" x 10" register would seem to have 100 square inches of area, but by the time you allow for the frame and vanes, there might only be an actual cross-sectional area of maybe 70 square inches. IF the vanes are adjustable, the more you angle them, the less area is left. So take a very close look at the specs for the register, to determine how much REAL area is left over. And also look at the "smoothness" of the design: registers that have lots of protrusions and sudden sharp edges will create turbulent air flow which is noisy. With better designs, the vanes are smooth and "aerodynamic", which creates a lot less turbulence. OK, so now you have your registers figured out: that automatically defines the duct that leads to the register! You have no options here. If the duct is 8" x 6", then the duct has to be AT LEAST 10" by 8", because it is going to be lined with 1" of duct liner on the inside, all around. Or if you are using round duct, then it needs to have the same "equivalent cross-sectional area" as the rectangle of the register. So now you know the correct size of your registers, and the correct size of the ducts that lead to the registers, and you know that you need a long straight section of duct right before the register, to reduce turbulence. But how long does that straight part have to be? There are various methods for calculating that, but a good rule of thumb is that it should be at least three times the smallest dimension of the duct. So if you are using an 8" x 6" duct, then you need at least 3x6"=18" of straight duct before the register. That's the ideal, of course, but frequently that just isn't possible in a studio. So you do your best to make it as long as possible, and aim for an even lower velocity at the register, to reduce the noise from turbulence even more. So, at this point you have your register size, duct size, and final duct length. Now you go another step back up the chain: the silencer box. Once again, there's a general rule here, that the cross-sectional area must change suddenly by a factor of at least two, where the air enters the box and where it exists the box. So normally the area inside the box is twice the area of the duct. In other words, if you figured that your duct needs to b 8x6, that works out to 48 square inches, thus you need 96 in2 cross sectional area (minimum) inside your silencer. So you could make it 11" x 9" which is 99 in2m or you could make the box flatter, for example 12" x 8", which is 96, or even 16" x 6" (also =96). OF course, in theory you could make it ultra-flat, at 96" x 1", but in reality that won't work, as the static pressure would be too high from such a system. So keep your dimensions reasonable, and never go below about 6" on the smaller dimension. However, once again, this is the cross-sectional area that the AIR FLOW sees, not the actual internal dimensions of the wood. Why would that be different? Because the box is lined with duct liner! Just like your rectangular duct there's 1" of true HVAC duct liner on each side. So if your calculations show that you need 12" x 8" internal cross section, then the interior of the wood box needs to be 14" by 10" at all points. Add the thickness of the wood, and you get the actual EXTERNAL dimensions of the box, at that point. Assuming that you are using 1 1/2" thick wood, you'd add 3", to get a final external size of 17" x 13". But that's just the width and height: how LONG does the box need to be? Well, you need a certain number of "baffles" inside the box: the more isolation you need, the higher the number of baffles. At the VERY least, you need two baffles. Probably three or four (usually). Maybe as many as five or six, for very high isolation needs. Each baffle is probably 1" thick plus 1" of duct liner on each side, so 3" thick. Plus the spacing between them (to get the same cross sectional area as above). So let's say you need three baffles spaced 12" apart, that works out as follows: (4x12) + (3x3) = 57" internal length, plus 3" wood = 60" total length. So for this hypothetical case, your silencer box would be 60" long, 17" wide, and 13" high. Did I mention that silencers are usually pretty large? :) So now we go yet ANOTHER step back up the chain: the duct on the far side of the silencer. How big should that be? Answer: it doesn't matter! As long as it is half the cross sectional area of the silencer interior, that's fine. If it is 1/4 the area of the silencer interior, that's also fine, EVEN THOUGH THE AIR FLOW SPEED WOULD BE MUCH HIGHER. It does not matter, because you'll never hear it! That can flow fast, or slow: it won't affect the noise level inside the studio, because it is on the FAR side of the silencer. Of course, there are limits: the smaller you make it, the higher the static pressure, and you cannot exceed the total static pressure that your AHU can handle. So you have to be careful when adding up all the ducts, silencers, registers, dampers, and other things, to make sure the total static pressure from all of those is less than the capacity of the AHU. If the static pressure is too high, the AH will not be able to run efficiently, the fan blades will stall, the motor will overspend, the service life will be very much shorter, and you won't get the performance you were planning on, either in terms of ventilation or in terms of cooling. And so on. You keep on working backwards up the chain, doing the math for each part, to make sure that you have the flow rates, flow velocities, and static pressure within the range that you need. "Range that you need"? What's that? Well, to dimension the actual AHU itself, you must ensure that it is able to move enough air to replace all of the air inside your room, at least 6 times per hour. In other words, if the volume of your room is 2000 cubic feet, then your AHU must be able to move at least 12000 cubic feet per hour, and if you divide by 60 then you get cubic feet per minute: 12000/60 = 200 CFM. For that room, your HVAC AHU would have to be capable of moving 200 cubic feet per minute (air flow rate) at a velocity that will produce no more than 300 FPM AT THE REGISTERS, on the highest setting. That's just the specs for how it moves air: in addition, you need to calculate the spec of how much heat it must be able to add/remove, and that, in turn, depends on the sensible heat load and the latent heat load. But that's an entirely different subject... That probably didn't answer your question directly, but there's enough info in there for you to be able to figure it out, I hope...

There seems to be some big confusion here: You do NOT need such low flow velocities inside the silencers: the oft-quoted 300 fpm figure is for the air velocity at the REGISTERS, not inside the duct-work. The velocity can be much greater inside the ducts and silencers, as long as there's a decently long section where it has already been slowed down just prior to the register. And especially on the part outside the outer leaf: the velocity out there really doesn't matter at all, as far as the studio is concerned (although it might matter for the neighbors...)

Assuming the register cover is directly on the outlet of your silencer box, there wouldn't be enough duct work (3 times the smallest dimension) to deal with turbulence. I've found that twice the cross sectional area of your inlet size often ends up being close to the <300 ft/min air velocity anyway. Thanks for sharing this info though as it will probably help me out with my lack of space in my ISO room! Greg

That probably didn't answer your question directly, but there's enough info in there for you to be able to figure it out, I hope...

Stunning, Stuart!! Thank you - yet again - for all this info! i feel armed, and ready!! Onward!!!!

i feel armed, and ready!!

Ahh, but we are just getting started! Barely scratching the surface, so far ... :) :lol: 8) - Stuart -

Ahh, but we are just getting started! Barely scratching the surface, so far ... :) :lol: 8)

Gotta start somewhere!

Thank you all. I got up at 5:30am because I was thinking about HVAC. It is such a roller coaster. After Greg's post I was "yeah" then after Stuart's I was "oh". Very helpful! Howie

Assuming the register cover is directly on the outlet of your silencer box, there wouldn't be enough duct work (3 times the smallest dimension) to deal with turbulence.

There can be enough, if you do it right. I often extend a long "sleeve" from the silencer box (which is in the air gap above the ceiling) down through the ceiling, then a bit more, and hide it behind treatment. That way I have the full depth of the ceiling joists, plus a couple of inches above the ceiling, plus a few inches extra down below, plus the thickness of the silencer box walls and dict liner, plus maybe most of the height of the silencer box interior. If you work it carefully, there's enough space, usually. - Stuart -

Plus the spacing between them (to get the same cross sectional area as above). So let's say you need three baffles spaced 12" apart, that works out as follows: (4x12) + (3x3) = 57" internal length, plus 3" wood = 60" total length.

How did you get 12" of the spacing between baffles on your hypothetical 6x8 duct? Thanks, Howie

How did you get 12" of the spacing between baffles on your hypothetical 6x8 duct?

I suggested several options for the internal cross sectional area of the silencer box in that post, but for this hypothetical situation, I chose the 12" x 8" option (the DUCT is 6x8, yes, but the internal cross section needs to be at least twice that, as I mentioned). Assuming th - Stuart -

Hello again, When combining AHU and HRV/ERV in a live room only setting, do they both tie into the same duct work or do they have separate duct work? Searched but I could find an answer. Thank you.

When combining AHU and HRV/ERV in a live room only setting, do they both tie into the same duct work or do they have separate duct work? Searched but I could find an answer.

Same system. Put the HRV in the ducts that would normally bring in fresh air from the outside world, and dump stale air to the outside world. Those same ducts would be there anyway: all you do is route them through the HRV. - Stuart -

Same system. Put the HRV in the ducts that would normally bring in fresh air from the outside world, and dump stale air to the outside world. Those same ducts would be there anyway: all you do is route them through the HRV.

That's what I thought. Thanks for confirming! Howie

Stuart, Greg, and Darth, I have a newly edited post in my thread called "Studio Planning Stage" with an HVAC plan and more here: viewtopic.php?f=2&t=21093&p=145598#p145598 I submitted this on April 27th but got no feedback. I have been editing it since then. I appreciate any advice you could offer. Thanks, Howie

Hello Team! long time.. finally closed escrow, and am moving forward with the studio quick question, if you'd allow me: most of the walls (all, probably) will be of the 'standard' 2layers drywall w. Green Glue + 2x4 + 2x4 +2layers drywall w Green Glue (double leaf setup) and I'm curious about what would (could) bring that design up to the 'next level' of isolation. there is a sort of main wall (on the drawing with the red oval over it) btw the studio and the rest of the building, and i'm curious to get your input re: making that wall better, isolation-wise. this is potentially the one spot where i could actually use some more isolation.. some things that come to mind would be: 1 more space btw the two leaves (i.e. the 2x4 frames) = i've got some room here, so.. would 12" be a dramatic improvement, over 1"? 2 more insulation btw the two leaves (for example: if nr1 is true, would one then fill that 12" gap with insulation?) 3 more / different material on the wall itself? 4 layers of drywall? or, one layer of drywall and one layer of something else? Like QuietRock? 4 different types of insulation? (R13 fiberglass seems to be the norm... is there a better choice for studios?) just looking to see what you think would be the next level, as it were... hope this makes sense! best Husky PS - the attached jpg is a sketch, so don't be too hard on me :-) it's all a work in progress...

Congrats on closing! That's good news.

most of the walls (all, probably) will be of the 'standard' 2layers drywall w. Green Glue + 2x4 + 2x4 +2layers drywall w Green Glue (double leaf setup) and I'm curious about what would (could) bring that design up to the 'next level' of isolation.

Only two things: 1) More mass on each leaf. 2) Larger air gap between the leaves. Either one, or the other. Or both.

there is a sort of main wall (on the drawing with the red oval over it) btw the studio and the rest of the building, and i'm curious to get your input re: making that wall better, isolation-wise. this is potentially the one spot where i could actually use some more isolation..

You cannot increase the total isolation of a studio by improving only one wall. Isolation is "all or nothing". The overall isolation is only as good as the weakest link. Not sure if you've seen my analogy of a fish tank before... if not, do a search on the forum for "aquarium", and you'll probably find it. A few times... :)

1 more space btw the two leaves (i.e. the 2x4 frames) = i've got some room here, so.. would 12" be a dramatic improvement, over 1"?

It would lower the resonant frequency quite a bit, yes, which will have an overall positive effect for THAT wall, but won't do much for the entire studio! You would need to do the same to the other walls, and the ceiling, and the doors, and the windows, and the HVAC system, and the electrical system...

2 more insulation btw the two leaves (for example: if nr1 is true, would one then fill that 12" gap with insulation?)

You ALWAYS fill the air cavity with suitable insulation, no matter how big or small it is, if you want maximum isolation. The purpose of the insulation is to damp internal resonances going on inside the wall cavity: no damping = worse isolation. The insulation fundamentally changes the way sound moves through the cavity: putting insulation in the cavity changes the process from adiabatic to isothermal and reduces the speed of sound by a factor of around 30% (debated). Look at the fixed "constant" in the MSM equations: it changes from 60 if the cavity is empty, to 43 if you fill it with suitable insulation. That alone should tell you something... If you don't fill the cavity, then you would have to set it higher than 43, which obviously implies worse-than-optimal isolation...

3 more / different material on the wall itself? 4 layers of drywall? or, one layer of drywall and one layer of something else? Like QuietRock?

Mass is mass. Sound waves cannot read price tags, and won't be impressed if you pay more than you need to for the mass. All the sound waves see is "kg/m2". The higher that is, the more they are attenuate. The price tag does not influence the mass. So get the cheapest mass that will do the job.

4 different types of insulation? (R13 fiberglass seems to be the norm... is there a better choice for studios?)

Use the type that best fits the application! You need the type that has the correct acoustic impedance for the job you want it to do. In other words, the greatest damping at the lowest MSM resonant frequency of the wall system. That will probably be in the range of around 7,000 to 10,000 MKSrayls for your ultra-thick wall, with very deep insulation. Perhaps a little lower than that, considering the thickness and very low frequency. I would suggest probably OC-701 or OC-703, but it's gonna be real expensive to put 12" of 703 in all of your walls and ceiling! It might be an idea to go with a slightly less capable insulation that is much cheaper. Unless of course you have very deep pockets, and don't mind blowing tens of thousands of dollars on insulation alone.

just looking to see what you think would be the next level, as it were...

Your diagram is faulty in several ways: 1) it shows that you have several "things", which I assume are support posts, connecting the junctions of some walls between rooms: that wont work. The support pillars would have to be totally inside the wall cavities, not touching any of the leaves. The way you show it would trash your isolation. 2) It shows that your "CPU room" (do you mean "machine room"?) is not isolated from the CR. That would likely be an issue if you have noisy gear in there, such as a few computers with large hard disks, and fans.... 3) You have the client couch right up against the rear wall. Read "Acoustic Absorbers and Diffusers: Theory Design and Application by Cox and D'antonio to find out why that's a bad idea. 4) The client couch is not symmetrical in the room: someone sitting back there is not going to get a balanced stereo image. 5) You don't have any bass trapping at all on the rear wall! And no diffusion either! What is your design concept? It looks vaguely like it wants to be RFZ, but the speakers are not flush mounted and the angles don't work for that, so that can't be it... Also, the "CPU" door is in the way of where your soffits would need to go. So it isn't clear what design concept you are using as the basis for this room. 6) The rear corner bass traps appear to be the only ones, which means they are far too small for that room. You'd probably need about five to ten times the volume you show there (unless this guy can make his magical physics-defying bass trap work! ( viewtopic.php?f=2&t=21607&p=145926 ). Have you read ITU BS.1116-3? It doesn't tell you what design concept to use, or how much bass trapping you will need, but it does lay out the full range of acoustic specifications you will need to meet in your room, if you want to use it for critical listening. That, in turn, will point you in the right direction... 7) You don't seem to have any sight lines from the mix position or the client couch into the vocal booth. 8 ) Your mix position layout doesn't seem to make much sense at all... more detail needed to see what is actually going on there. 9 ) Your amp booths don't seem to be isolated. 10) You seem to have some type of huge door, about the size of a garage door, into the LR at the bottom left of the diagram: :shock: How do you plan to isolate that? !!! If you do that, you certainly won't be getting much isolation. 11) What is the rectangle marked "EL" at the bottom center of the diagram?

just looking to see what you think would be the next level, as it were...

Overall, I'd suggest that before you strat thinking of "next level", you should define "this level"! :) In other words: define how much isolation you NEED, define your CR design concept, define your room volumes and floor areas, define your basic treatment, then update your floor plan to reflect that, and also move form 2D into 3D. Once you have that in place, you can do teh math to figure out how much isolation you will actually be getting with the current design, compare that to how much you need, and then decide if you need to go for the "next level" or not. Hope all those comments help! - Stuart -

To add to what Stuart mentioned, - all of your ISO booths have doors right in the corners of the rooms. This is where you're going to need bass traps. Small rooms like that need all the bass trapping they can get. - all of your wall gaps are small which means we're assuming all of your HVAC duct work and silencer boxes are going to live in the ceiling. You have the height for this? - there is no sight line between ISO 2 and ISO 3. This is assuming all of your doors have large glass in them. - speaking of glass, we all love the look of glass, but damn, you're going to spend a fortune on glass for this project!!! Is all of the light grey stuff glass? I'm referring to your super thick outer leaf wall. If so, if all of that is existing glass in the building, you're going to have to replace that with appropriate glass. Again, that looks like a ton of glass, maybe literally. Greg

Hey!!! thanks for this.. so, more space, more mass good to know i'll take the other points into consideration, for sure and like i said, it's a work in progress this sketch is really for the layout (of the whole building) - so yes, bass traps, etc have not been drawn in to completion and the couch.. clearly that's movable.. just there for visual joy - for now it's possible that i'll add some bass trapping on that back wall. re. sight lines, all the doors will have glass in them, so the sight lines are pretty decent some things could be better, but this is close, i reckon. re. insulation: what do you typically use for the wall cavities? obviously, the R13 stuff is most economical, but i'd like to see what the 'next level' up from there is.. thanks for all this!!! PS - the EL is an elevator down to the first floor parking... studio is on the second floor - and yes, the gray is glass - original glass / windows in the building will all be replaced!

Hello again! Quick question: Do you guys have any experience with any of that "underlayment" for hardwood floors? A lot of "soundproofing" companies sell this stuff (MLV for example) as "ideal under hardwood floors, etc. My studio will be on a second floor, and will probably have hardwood floors (on top of a concrete floor) Does any of that stuff help with isolation (from the lower floor)?? Or is it all snake oil?? Husky

This doesn't directly answer your question as my information here applies to underlay with carpet, not hardwood, but: You can read more about this in chapter 12 of www.roletech.net/books/HandbookAcoustics.pdf Greg

Thank you for this, Greg! this is helpful every little bit is helpful much appreciated! Husky

PS - spoke with an acoustics guy on the phone today, about walls and air gaps and stuff. He said 4" of insulation on either side is the way to go. No matter what the air gap btw the 2x4 frames is (be it 1" or 12") - but others say "fill it all up" - so, once again, conflicting reports. One would think that filling a 12" gap with insulation would be BETTER than not filling it... oh well flip a coin, i suppose :)