Flaco's Basement Studio in San Francisco

Hi all. I've been reading this forum (and Rod Gervais' book) for the past year, and I'm now posting because I'm ready to make the plunge. I'm going to build a room in my basement mostly for music rehearsal, but which may also serve as a very basic recording space as well. The main goal is to achieve maximum sound isolation to avoid bothering the neighbors and my own housemates - especially for drums and electric bass. If I'm lucky I'll have enough isolation to jam in there with the rhythm section of my brass band: 3 drummers and a sousaphone! Some basic background: I own the house, which was built on a slight hillside in 1902, and which is almost a rowhouse, but not quite -- there is 1" of space between my house and the other houses on both sides. I am building the new room in the dirt-floor basement, which means I will be pouring a new slab for this room, which won't touch any existing foundations. Other important details about the existing space in the basement: the cripple walls above the foundation are covered on the exterior with 3/4" redwood lap siding, then there is empty airspace in the bays, then 5/8" structural plywood sheathing on the interior. The plywood has 2" holes drilled at the top and bottom of each bay, for ventilation (that is code here). The ceiling above the basement is old two-inch thick plank subfloor, redwood maybe? It's not perfectly planed so there are small gaps between planks and they are not uniform width. They are supported on dimensional 2x6 joists. Above them is 1 inch thick tongue in groove, perhaps on top of some plywood but I can't quite tell. There's a lot of mass there, but also lots of holes and gaps and cracks because it was built a very long long time ago. I have already dug out an additional 24" in the basement in the area where the room will be located, careful to avoid disturbing soil in the 45 degree plane away from existing foundation and supporting posts. Once I pour the new slab and stem walls, I will backfill those 45 degree areas. I had to replace two posts that are in the middle of the dug out area, because I needed to put in new footings for them at the new 2' deeper level. Currently there is 8 feet of space between the top of the new concrete footers for those posts, and the beam which spans through the middle of the space. There are some water pipes which I need to re-route, and a clothes drier vent I need to re-route, but that should be easy. You can see the existing space in the photos, and you can also see I have already done some sketchup drawings for my imagined room. I am not necessarily attached to the design I already have; I'm looking for the biggest possible space without encroaching further on existing foundation walls or load-bearing posts, which has maximum sound isolation (and hopefully doesn't sound like garbage inside). Currently the proposed interior dimensions of the room will be about 11' wide, 15' long, and 8' tall. I looked at Bob Golds mode calculator, and it looks like it will work pretty well at those dimensions. As you can see from my sketchup shots, I plan on building double wall assemblies using 2x4 framing 16" OC and including double-gypsum (5/8") on the inside side of the inner wall and the outside side of the outer wall, with fiberglass insulation in the middle. I will use a 1 inch space between the two plates of the double wall assembly. I MIGHT also beef up the existing ceiling by adding gypsum in between bays (possibly two layers). Certainly I hope to build a totally decoupled independently framed ceiling, with two layers of gypsum hung from that in the interior of my new room. I like John's inside out walls, but since I am shooting for maximum isolation, I figured I should go with Rod's designs instead, and then add my room treatments afterwards. I realize that this design looks a bit like a triple or quad leaf design, and I understand the problems of that, but hear me out: the existing cripple walls don't have much mass, and the new room is going to be built far away (two feet away on one side, one foot away on the other, because I had to dig down). My existing cripple walls give very little isolation currently, so I am just leaving them mostly out of my calculations. My budget is probably less than $10,000, doing most of the labor myself and with friends. I haven't gone into details about caulking, firestopping, etc. but I think I'm aware of most of those issues and there seems to be general consensus on best practices there. My biggest concern / question is: how can I construct an independent ceiling assembly around that damn beam and HVAC run, without sacrificing too much headroom? I figured I would build a soffit around the beam and HVAC, but I still haven't figured out the most elegant way to frame the independent ceiling around that area. Or do I need to do some iso hangers? I'd prefer to avoid that route, but I'll do what I gotta do… I was working in sketchup, then got stuck at this point. Maybe I need my top plates to be lower? My next question is: to Green Glue or not to Green Glue? Those double layers of gypsum look pretty beefy, but if the GG will really help add isolation, I'll bite the bullet. I've read many many posts, but I'm still unclear: is there any consensus around here on that question? Finally if there are any other ideas, concerns, suggestions, problems you see with my design, etc. please by all means let me know. I want to pour concrete in the next two weeks if possible. Best, Flaco

Hi there Flaco, and welcome! :)

If I'm lucky I'll have enough isolation to jam in there with the rhythm section of my brass band: 3 drummers and a sousaphone!

I see you like to set lofty goals, don't you!!!! :)

I will be pouring a new slab for this room, which won't touch any existing foundations.

That's a good start, but you should get that part designed professionally, by a structural engineer. Especially so, considering where you leave: earthquakes.... You are doing major structural modifications, including digging around your existing foundations, so that should be properly supervised, and with the relevant permits and inspections.

...covered on the exterior with 3/4" redwood lap siding, then there is empty airspace in the bays, then 5/8" structural plywood sheathing on the interior. The plywood has 2" holes drilled at the top and bottom of each bay, for ventilation (that is code here).

That might be an issue, for both acoustic isolation (it's a 3-leaf system, to some extent, and possibly also a tuned trap of some type), as well as ventilation: there won't be any! Since all of your leaves must be sealed air-tight, there won't actually be any air flow through there. You should probably get professional help there too, in deciding how to proceed and still meet code.

I plan on building double wall assemblies using 2x4 framing 16" OC and including double-gypsum (5/8") on the inside side of the inner wall and the outside side of the outer wall, with fiberglass insulation in the middle.

Taking into account your existing 2-leaf wall, you are talking about four leaf walls there? :shock: It's hard to see, but your diagram does seem to show large gaps around two sides of the new build, but only very small gaps on the other two sides. They might become problematic....

I MIGHT also beef up the existing ceiling by adding gypsum in between bays (possibly two layers). Certainly I hope to build a totally decoupled independently framed ceiling, with two layers of gypsum hung from that in the interior of my new room.

For the level of isolation you are talking about, I would change that "I MIGHT" to "I absolutely, unquestionably MUST...". For high levels of isolation, BOTH leaves need considerable mass, perfect seals, and a large, damped air gap between them.

I like John's inside out walls, but since I am shooting for maximum isolation, I figured I should go with Rod's designs instead, and then add my room treatments afterwards.

There is no difference at all for isolation. The ONLY difference with John's design, is that the studs go on the "other" side of the leaf itself. All other things being equal, John's design will isolate to the exact same level as a normal MSM wall. What matters for isolation is two factors only: The amount of mass on each leaf, and the distance between the leaves. If those two are the same, then the location of the studs is irrelevant: putting the studs inside the wall cavity or in the room makes no difference.

I realize that this design looks a bit like a triple or quad leaf design, and I understand the problems of that, but hear me out:the existing cripple walls don't have much mass,

You said they are 3/4" redwood siding on the outside: that's about 500 kg/m3, which works out to roughly 10 kg/m2 surface density: I'd call that pretty massive! You also so that inner-leaf is 5/8" plywood, which is about the same density but a fraction thinner, so that works out to 8 kg/m2. Also pretty substantial mass.

and the new room is going to be built far away (two feet away on one side, one foot away on the other, because I had to dig down)

That helps, and you are probably OK on the 2 foot side, but I'm not so convinced about the 1 foot side... Did you do the mat on those, to figure out your MSM resonance?

My biggest concern / question is: how can I construct an independent ceiling assembly around that damn beam and HVAC run, without sacrificing too much headroom?

That isn't your only problem: you also have those structural support posts coming down through your room, and since those are part of your OUTER leaf, you will need to soffit those in as well, by building an inner-leaf around them. They are direct flanking paths through your ceiling. Sure, there's not a lot of surface are to them, but you are talking about very high levels of isolation, so I would definitely do that. But to answer your actual question there: I see only two options: 1) drop your top plates to the height where you can span the entire room below those beams with suitable joists (what dimension joists have you calculated for there? Big question!), or 2) use isolation hangers from the existing joists, PROVIDED THAT your structural engineer does the math and tells you that it is OK to add the huge extra load of that new ceiling. My guess is that you might not be able to do that, since that crawl space does not seem to have been designed with a ceiling in mind, so the current dead load and live load might already be close to the design limit.

My next question is: to Green Glue or not to Green Glue? Those double layers of gypsum look pretty beefy, but if the GG will really help add isolation, I'll bite the bullet.

If you want high levels of isolation at low frequencies (eg, drums...) then GG is a great way of getting that. It isn't about mass: it is about constrained layer damping, which is what GG does very well.

I've read many many posts, but I'm still unclear: is there any consensus around here on that question?

That depends on what you need to accomplish, how much you are prepared to spend on accomplishing it, and physical limitations of your build. The basic question: Does it work! Yes! resoundingly. The published results form independent lab tests show that it has a very useful effect on low frequency isolation, which is the part of the spectrum that is the hardest to isolate anyway. So form that point if view, it is good stuff. However, it is not cheap. So if your budget can handle it, then it is worthwhile. If not, then you can get about the same effect from adding another layer of 5/8" drywall. However, that too has a budget impact, and also a space impact (makes your room narrower, and ceiling lower), and a structural impact (lots of extra mass). So you have to weight up the factors and reach your own conclusion relevant to YOUR room and YOUR budget and YOUR goals. What makes sense for someone else might not make sense for you. But if the question is "Does GG work as advertised, and is it useful in a studio build?", then the answer is "Yes".

Finally if there are any other ideas, concerns, suggestions, problems you see with my design, etc. please by all means let me know.

HVAC and electrical: I don't see any of that on your plans, and the are both huge, big, major, important parts of all studios. I would make sure you have those fully covered in your design, before you do any more physical work. I would also make sure that your structural engineer signs off on everything you are talking about and planning, before going any further! - Stuart -

Thanks for the response, Soundman. I am indeed hoping for great things....and with the combined knowledge of all the helpful folks out here, I think I can achieve some great results (along with my locally sourced experts, of course). So I am plunging ahead, with a perhaps imperfect plan, but I would love to get feedback on ways to improve it. I've poured a concrete slab, with rigid foam between the existing foundation on one side (and surrounding the two footings for the posts in the middle of the room), so the new concrete doesn't connect directly to the old. Don't worry - I had expert help signing off on all that work. The engineering has been evaluated. I decided not to do a stem wall after all, as you can see in the photos, but I am still doing a double wall assembly, spaced 1" apart. I might run into some quadruple-leaf issues on the one side, since it turns out to only be 6-8" away, but I'm now planning on doing triple layers of 5/8" gypsum with GG sandwiched (on the inside of the inner wall, and the outside of the outer wall), so I hope to eliminate most sound before it even gets to the third leaf. I don't know how to do the math to calculate the MAM resonance, so I suppose this is just "doing the best I can", but please tell me if I'm wrong. This way I don't have to mess with the existing house at all, so there won't be any moisture issues or seismic issues. It's only a problem with that one wall anyways -- the other one is 33" away, so there will be no extra-leaf issues there anyways. The new slab is about 10'x14', with those pesky posts in the middle. As you mentioned, I'll have to frame aroudn those and do double or triple layer gypsum with GG there too. I've decided to move the HVAC duct out of the area completely, so there's just that beam in the middle to contend with, no other funny business. I'm indeed giong to have to beef up the existing ceiling, even though I have a really beefy ceiling already. You can see in the photo of the HVAC cut-out how thick the ceilng is -- It's 2" dimensional planks of doug fir, with 3/4" slats atop, then 3/4" tongue in groove flooring. That's a lot of beef already, but it's not SEALED, so I'll add one layer of 5/8" with GG directly to the ceiling using drywall screws, and then use backer rod and acoustic caulk on edges to get that tight seal. As far as inside out walls, all I meant is that usually they are built with a smaller airspace, which is less effective for low freq TL. They don't NEED to be built that way, but that is often cited as an advantage - they take up less space. Since I dug down far enough, I'm going to err on the side of better isolation, with a bigger airspace. Yes? As far as electrical and HVAC, it's true I haven't included them in the drawings, but I certainly have been thinking about them. I've just ordered two Panasonic Whisperline 340 CFM inline fans, and I'm planning on building two dead vents on the outside of the outer wall, as diagrammed by Ted White on the Green Glue website. The fans will be controlled by a single dimmer switch, one pulling air in, one pushing air out. As far as electrical, I'd like to do some wall mounted sconces, not in the corners so as not to interfere with traps, and some surface mounted boxes, so I can avoid those giant holes in the drywall. The remaining issue is still the one I am mulling over:

My biggest concern / question is: how can I construct an independent ceiling assembly around that damn beam and HVAC run, without sacrificing too much headroom? But to answer your actual question there: I see only two options: 1) drop your top plates to the height where you can span the entire room below those beams with suitable joists (what dimension joists have you calculated for there? Big question!), or 2) use isolation hangers from the existing joists, PROVIDED THAT your structural engineer does the math and tells you that it is OK to add the huge extra load of that new ceiling. My guess is that you might not be able to do that, since that crawl space does not seem to have been designed with a ceiling in mind, so the current dead load and live load might already be close to the design limit.

I don't want to use isolation hangers, since I have the ceiling height and I want true isolation. I also don't want to span joists completely underneath the beam, because that would put my final ceiling height at 7'4 or so, instead of the 7'11" I could get with the following plan... Right now the plan is to run the joists lengthwise, 14' or so, even though this means they will be perpendicular to existing joists (and so they can't "nestle" in). Calculations indicate 2x6 spaced 16" OC will work with this load and length. By running the joists this way, I am running parallel to that giant beam, which makes everything much much easier. I will just have to frame out a little extra soffit for the beam, only an inch or two lower than the rest of the ceiling. The other option would be to run the joists parallel to existing, so I could nestle them up high, but then I would have to create another beam on EACH side of the existing beam to carry the load of the joists. That sounds like a nightmare. So I think I am going with the new joists running perpendicular. However, I am a little confused by an issue that probably has an obvious answer: how do I create a tight seal for the OUTER wall, where it meets the existing ceiling joists? I am looking through Rod's book, probably staring right at the answer, but I can't seem to get it. The top plates of my outer wall are going to be just 1/4" lower than the existing house joists, perpendicular, then attached to those joists with Simpson Strong-Tie Truss Clips (as shown in Sharward's build thread) - so the outer walls don't become truly load-bearing walls. So how do I fill the big gaps left in the joist bays above? Obviously they will have "beef" in the area directly above the room, and they will have insulation -- but that will stop at the perimeter. Do I need double (or triple) drywall going all the way up into each joist bay, fireblocking (and soundblocking) each one?

I'm now planning on doing triple layers of 5/8" gypsum with GG sandwiched (on the inside of the inner wall, and the outside of the outer wall), so I hope to eliminate most sound before it even gets to the third leaf. I don't know how to do the math to calculate the MAM resonance, so I suppose this is just "doing the best I can", but please tell me if I'm wrong.

That's the crazy thing about acoustics: what seems logical and intuitive often isn't correct. It turns out that, for a three leaf wall, it is most effective when the air gaps are the same size, and most of the mass is on the middle leaf. The optimum point is where the middle leaf has as much mass as the other two COMBINED. That also makes the calculations easier... :) I'm not so sure about 4-leaf, though: There isn't a lot of research out there on 4-leaf walls, since they aren't very common. The only thing I can tell you about 4-leaf walls is that the isolate even worse than 3-leaf at low frequencies, and isolate much better at high frequencies (24dB/octave for 4-leaf, vs. 18 dB/octave for three leaf, 12dB/octave for 2 leaf, and 4 to 5 dB/octave for single leaf. Those are empirical real-world numbers, a bit lower than theoretical prediction.

As you mentioned, I'll have to frame aroudn those and do double or triple layer gypsum with GG there too.

The framing cannot touch the posts, of course, so that will be a pain. And you might not need GG, since they drywall won't be very wide, and will therefore be pretty rigidly held in place by closely spaced framing. Of course, GG certainly won't do any harm there! So go for it if you have the budget.

I've decided to move the HVAC duct out of the area completely, so there's just that beam in the middle to contend with, no other funny business.

Great! But you still need to put your own HVAC ducting somewhere...

As far as inside out walls, all I meant is that usually they are built with a smaller airspace, which is less effective for low freq TL. They don't NEED to be built that way, but that is often cited as an advantage - they take up less space. Since I dug down far enough, I'm going to err on the side of better isolation, with a bigger airspace. Yes?

Ahhh! Ok, that makes sense. Yes: bigger air space = better isolation, and more insulation in the air space also = better isolation.

The fans will be controlled by a single dimmer switch, one pulling air in, one pushing air out.

It would be better to buy a proper speed controller for your fans. Are you sure you need 340 CFM? Seems like a lot... how did you arrive at that number? What size ducts are you using? What is the volume of the room?

Right now the plan is to run the joists lengthwise, 14' or so, even though this means they will be perpendicular to existing joists (and so they can't "nestle" in). Calculations indicate 2x6 spaced 16" OC will work with this load and length. By running the joists this way, I am running parallel to that giant beam, which makes everything much much easier. I will just have to frame out a little extra soffit for the beam, only an inch or two lower than the rest of the ceiling.

That sounds like it should work, but it would be good to see a diagram.

I am looking through Rod's book, probably staring right at the answer, but I can't seem to get it. The top plates of my outer wall are going to be just 1/4" lower than the existing house joists, perpendicular, then attached to those joists with Simpson Strong-Tie Truss Clips

:?: Your outer wall actually MUST be attached to the rest of the outer leaf. No separation of isolation hangers needed. The top plates can tie in directly to the existing structure, even though those walls will not be load-bearing. It's just like any other non-loadbearing wall in your house. Use blocking between joists to complete the framing, and take the drywall all the way up, even if you have to cut "zig-zag" shapes to make it fit. Backer rod, caulk, etc. However, there may well be fire-code restrictions on doing that, so check with your inspector first, to make sure it is allowed. - Stuart -

Thanks again for the feedback, Stuart. Regarding the last thing, first: I've attached a sketchup file and some screenshots to show the area in question, highlighted lavender: this blocking between existing ceiling joists should be built with triple-5/8" gypsum, on top of the wood blocking? I think I understand from your mention of zig-zag gypsum that you mean I should run the outer layers of gypsum (all of them!) all the way up between those joists if possible, in that lavender area. Yes? In that sketchup file the white areas are fireblocking (a 2x4 running on one side, a section of 5/8" gypsum on the other) which will close the gap at the top plates to between 1/2"-1/4". Then I will spray fireblocking foam in between to complete the fireblock without acoustically connecting the two walls. On the triple/quad leaf question, I guess I'll just beef it up and live with the results. Thanks for explaining it a bit more. On the center columns, I agree -- framing won't touch existing post or beam above, which will be a pain. And I'll forgo the GG there -- what you said about rigidity there makes sense. I wasn't planning on running any HVAC inside the room -- just an intake and a return grille on the walls, as shown on Ted White's diagrams. The fans may be oversized -- I'll be running 6" ducts, which will need to make a run of at least 20' after leaving the dead vent. I could do the 20' run in rigid ducting with as few turns as possible, if it makes sense, since the dead vent (which uses flex duct) should take care of most of the sound issues. That would help keep airflow happy. I admit that the HVAC plan is a very rough estimation -- I prefer to have it oversized, but would love to keep it as quiet as possible too. I may have as many as 8 musicians in there at one time (brass band! yes it will be ridiculously cramped, but we've done it before!) - so we need plenty of airflow. Here in SF we don't need AC, and if we occasionally need heat I can use a small space heater. It's great to have your feedback -- thanks a million. - Flaco

I think I understand from your mention of zig-zag gypsum that you mean I should run the outer layers of gypsum (all of them!) all the way up between those joists if possible, in that lavender area. Yes?

Right!

Then I will spray fireblocking foam in between

I would prefer to use fire-rated acoustic sealant, rather than foam. Most types of foam don't have enough mass to be useful, acoustically.

I wasn't planning on running any HVAC inside the room -- just an intake and a inside the room or outside, to keep both the temperature and humidity under control. That room s going to be double-sealed, absolutely air-tight, and wrapped with multiple layers of very effective thermal insulation. Heat builds up really fast in there, and so does humidity.

The fans may be oversized -- I'll be running 6" ducts,

:shock: 340 CFM through a 6" duct implies air velocity of over 1700 fps!!!! That's about TEN TIMES faster than it should be for a studio, ideally: your registers are going to sing and whistle, loudly. Very loudly. Something like 50 dB, just from the air movement itself, without considering the large amount of extra noise from the registers... The general recommendation is that air flow speed should be no more than 300 fps at the register, and ideally under 150 fps. So yes, your fans are way, major, big-time oversized for 6" duct! You can't guess with HVAC: You need to do the math. First, figure out what is the MINIMUM legal flow rate you need in your rooms, which is set by your local building code requirements for habitable spaces. then check that against ASHRAE recommendations for the type of room, the volume, and the occupancy. Size your fan according to that... BUT with caveats: you will need to adjust for the static pressure load. With the fan sized correctly for the room, determine the duct size that will keep the speed under 300 fps. Based on that diameter duct, and the type and length of the duct, you can then figure out the predicted static pressure of the HVAC system, and based on that adjust your selection of fan so you get the right flow rate for your static pressure. With all that in place, you can then design your silencer boxes accordingly.

I've just ordered two Panasonic Whisperline 340 CFM inline fans, and

If you check the specs, those are actually rated at 372 CFM, so the air velocity will be even higher...

I could do the 20' run in rigid ducting with as few turns as possible,

Actually, you need as MANY turns as possible! Each turn helps with isolation, as sound tends to want to continue in straight lines, rather than going around the corners. So each 90° bend attenuates any sound that might have gotten into the duct.

since the dead vent (which uses flex duct) should take care of most of the sound issues.

That dead vent design is not appropriate for what you are trying to do. It will not accomplish what you are hoping, since it is not meant for that, and was never designed to do that. It is designed for one thing only: to silence fan noise. So the noise made by the fan itself is muted a bit. That is vastly different from what a proper HVAC silencer box does. Not the same at all. If you go with that dead vent design, then you will NOT be silencing your HVAC system. All you will be doing, is quieting the noise of the fan motor.

I prefer to have it oversized,

With HVAC, you cannot be either oversize or undersized. You have to be "right sized". If your flow speeds or flow volumes are too high, then you crate air noise and the movement of air through the room will be noticeable: you will feel the wind blowing through the room. If the flow rate is too low, then you will have stuffy, unpleasant conditions in the room. If you don't remove enough humidity, then you run the risk of mold and fungus forming in your room and HVAC system. If you remove too much, then the air becomes unpleasantly dry. Either way, your musical instruments and some types o microphone suffer, as they are sensitive to humidity. If the temperature is too high, it is unpleasant to work in the room, and you run the risk of damaging your electronic equipment, as well as your instruments, and affecting your mics. If the temperature is too low, that is also unpleasant, and can also cause issues with instruments, gear and mic. HVAC needs to be sized right, not guessed.

I may have as many as 8 musicians in there at one time (brass band! yes it will be ridiculously cramped, but we've done it before!) - so we need plenty of airflow.

:shock: Yes, you certainly do. In fact, you need a variable system with a controller, since there will be major differences when you have just one person on the room sitting quietly as compared to having all 8 going full-bore with a great jamming session. There's a major difference in human heat and humidity output for sitting quietly and strenuous exercise. A factor of about ten, in fact. So comparing the "one guy sitting quietly" to the "eight guys jamming heatedly", there's a difference of about EIGHTY TIMES the heat load in that room, just from the human bodies, without even considering the heat load of the equipment. That's a major difference. You need an intelligent controller with a thermostat at the very minimum, and ideally also with a humidity sensor, and perhaps even CO2 sensor. And you need an air conditioner capable of dealing with the heat and humidity load of eight people doing strenuous exercise, but that can also be slowed down to not be underloaded when there is only one person on there.

Here in SF we don't need AC,

Ummmm.... sorry, but yes you d:o. In that room, for the conditions you have described, you have no choice. This is not a luxury, not even a "nice to have". It is a basic necessity. Without it, that room will become very unpleasant, very fast. Without it, your instruments, mics and friends will all suffer. Without it, the room very likely wont even be legal. Overall, I get the impression that you are greatly underestimating the importance of HVAC in a home studio. I would seriously, seriously suggest that you need to do more research on this aspect of your studio, or hire an HVAC consultant with studio experience to do it for you. Not just any HVAC guy, but one who understands the specifics of studios. Sorry if I'm coming across a little harsh on this, but it real does seem that you aren't taking HVAC anywhere nearly seriously enough. I'm hoping that my "harshness" will nudge you in the right direction: HVAC is a major issue for home studios, and is frequently overlooked, but it's a serious issue, and is quite literally "life or death". Putting 8 people in a hermetically sealed container can indeed lead to health issues... - Stuart -

Hi again. Thanks for the reply. I'll respond in order here, then give a general update after. re: Foam: I was thinking mineral wool, but since Rod Gervais gave his blessing on fire-blocking foam on spaces less than 1/2", I thought that sounded a lot easier. See this thread here http://www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=14452&hilit=fire+block&start=15 . I'm not too attached to that idea though. re: HVAC: I appreciate the direct advice. I much prefer any "harshness"! However, I have to respectfully disagree with some of it, and take other parts of it into consideration. Regarding AC in San Francisco, perhaps you're not familiar with the climate here: in my northern-facing basement studio, the temp has never risen above 75 degrees. Humidity is pretty manageable too. I've been playing music here for many years and never in a single space that has AC... I'm not going to have a room full of sensitive recording equipment either; this is mostly a rehearsal room. Since my room is generally not going to be used as a recording studio, I'm not as concerned about some slight noise from the ducts pushing through a lot of air. Of course, it's probably better to design things with bigger ducts to avoid that, so maybe I'll reconsider. I suppose it's possible that the "whisperline" 372 CFM fans are not exactly "whispering" through the 6" ducts... though I've had great success with their other "whisperline" fans -- much quieter than comparable fantech fans. My whole idea was to get a fan system that was a little oversized, because, as you say, I want a variable controller to accomodate different situations -- one person vs. 8 people jamming is VERY different. I think the dead vent design I'm looking at is actually much better at silencing lower frequencies than the typical "silencer boxes" folks are using, with the "muffler" style maze pathway. Low frequencies just plow right through those little maze barriers. Those seem good for screening out high frequencies, but without the larger mass of the dead vent, I don't think they will do what I want to do. I've read several threads on the merits of various designs, and Ted White's dead vent design seems pretty solid to me -- at least in theory. But I could be talked out of it, if I was pointed to some logical reasoning showing that. The idea of the dead vent is that you use a small section of flex duct inside a giant heavily-drywalled box (outside the studio) filled with insulation, and the variable path of the flex duct sends the low and high frequencies into the insulation and double-drywall layers of the surrounding box. Then you do the rest of your duct run with rigid duct. Read more here: http://www.avsforum.com/t/1256990/post-your-dead-vent-and-hvac-pics/90 As far as the duct run outside the studio, I was thinking of only including one or two turns, because I want to keep static pressure down. I'd prefer to attenuate most of the sound BEFORE it gets to the outside duct run, because that's in an un-soundproofed area. (I know people hate the term "soundproof", but you get my meaning). Anyways, I'd love to follow your advice about doing the math to calculate the fan & duct size perfectly, but the truth is that I really don't understand it well enough myself to do that. And it's not important enough to me to have a totally quiet system (inside the rehearsal room, that is) for me to pay a lot to a professional HVAC person. All I really want is a variable system that can do a LOT of airflow, which keeps the noise inside the rehearsal room. A quiet system would be preferable, but honestly I'm not sure if I can afford it or learn how to calculate for it. Any help on more specifics would be great, but if not, I am confident this will work (since I have been reading about several others who have used similar systems). I hope I don't sound dismissive here; I really appreciate you taking the time to respond. Clearly you know more about this than me, but for my purposes I'm not sure if I can afford / understand how to follow your lead. Does that make sense?

Just read your recent thread on dead vent vs. silencer boxes, and it was interesting: http://www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=17603&start=60 The main takeaway for me was that the silencer boxes create an impedance change based on the diameter of airflow area -- which the dead vent doesn't do. However, the dead vent does disperse the sound through the thin membrane of the flex duct, so I'm still considering which might be most effective for the amount of time required to build it.... I think my fans will still work (others are using Fantech FG6, which is similar CFM). We shall see!

Some photos of progress. I wish I could upload higher resolution photos, but the limit seems to be 150k? True? 1. You'll see that we moved the ducts all out of the space where the room will be. 2. We beefed up the area between joists with one layer of 5/8" quietrock (found on super-discount, used, for $7 a sheet) -- greenglued to the wood above, and sealed around the perimter with backer rod and OSI-175. 3, 4, 5. To build the wall that had only 6 inches of clearance from another wall (yes, I know -- triple leaf), we had to frame it, then take off the plate bolt nuts and tilt it over, then put the plywood and two layers of 5/8" drywall (with GG sandwiched). It went back up without a hitch. Next we have to build a little mini wall above it, to finish the connection all the way up to the ceiling. There are some annoying duct runs and water pipes that have to be built around a little bit up there, but it's mostly pretty clean.

Regarding AC in San Francisco, perhaps you're not familiar with the climate here:

I am, actually. I've been there several times, at various times of year, so I've got a reasonable handle on that: typical moderate seaboard climate, generally cool and humid, no real extremes. But that isn't even the issue. You seem to be assuming that the place where you live is the key factor in designing your HVAC system, when in reality it isn't. It's only one factor among many, and not a huge one anyway. The point that you seem to be missing is that your ROOM and its OCCUPANCY are the issues, not the geographical location where it exists. Your room will basically be not one but TWO totally air-tight shells around you, and each of those is a perfect hermetic barrier: it does not allow air in or out. (If it did, then you would have no isolation: Where air goes, sound goes.). So you have two massive, sealed, airtight barriers around you, ISOLATING you from the outside world (which happens to be called "San Francisco" in your case, but could just as well be called "Miami" or "Anchorage" or "Sahara"). Then, to complicate things even more, each of those perfect and massive air barriers is lined with a huge, thick, very effective amount of thermal insulation, many inches thick. A nice snugly, warm, blanket. So you firstly have two layers of sealed dense thermal mass around you, then you have two layers of thick thermal insulation around you... Guess what: You are isolated from San Francisco! It isn't there. You could put that same room in the middle of the Amazon jungle, the Atacama desert, or the South Pole, and there wouldn't be a huge amount of difference to the HVAC requirements for the room. The issue is the room, not the surroundings. Sure, the finished room with nothing in it and the doors wide open will take on the climatic conditions of outside, but as soon as you close the doors and put people and equipment inside, that changes pretty fast, since the room is now absolutely isolated from the external environment. With the doors closed, you are totally sealed off from the outside world. So you have your isolated room. And you have people in it. And equipment. You say you aren't inclined to do the math, but the math is critical to understanding this, so I'll do some of it for you, and hopefully show you where you are going wrong, so that you an do the rest. For argument's sake, lets say you first have just yourself in your room, sitting very still doing nothing, then you have have your 8-man band in there, playing hard. The human body at rest puts out roughly 80 to 100 watts of heat. About the same as an old fashiined hundred watt incandescent light bulb. And in terms of heat energy, that's about 350 BTU per hour. Let's say you have a couple of lights turned on in there as well, so you can see, and a computer with a screen on it, and a small practice amp hooked up to your electric guitar. That's another 200 watts or so (conservatively), for a total of 300 watts, which is about 1000 BTU/hr. So just with you sitting there DOING NOTHING AT ALL, and a very minimal set of equipment, you are already producing 1000 btu/hr of heat energy, and it has no place to go! There are only three ways that heat can get out: radiation, convection, and conduction. Your room is totally isolated, so there is zero conduction going on. There are two perfect air barriers around the room, to there is no convective mixing going on. And the room is lined with major thick layers of thermal insulation, so there is no radiation going out either. All of that heat stays inside the room, and soon it starts getting warm. You could handle that with a very small air conditioner, say about 5,000 btu/hr capacity, and it would run on a duty cycle of about 20% on, 80% off. No problem. Set the thermostat for, say 70°, and as soon as the temperature inside the room hits that point, the A/C would run for about 12 minutes every hour, on and off. But now your seven buddies arrive, with their gear. Let's say that it includes a couple of electric guitars with decent amps (say a nice Mashall stack, and a Fener stack), some effects pedals, two keyboards, each with its own amp, a drum kit, a bass guitar with its own amp, a couple more computers, some mics, a small console, and some floor wedges. Maybe a couple of cell phone chargers, and an iPad charger too, to complete the picture. And maybe you turn on a couple more lights, perhaps on dimmers, to get the mood nice, and so the singers can read their lyrics, and the musicians can read their sheet music. Call it a total of maybe 2,000 watts of power consumption (very conservatively). So now you guys start playing, and get into a fantastic jamming session. The human body doing strenuous exercise does not put out 80 watts: it puts 1,600 watts! But lets be conservative, and say that you guys are only jamming at less than full capacity, and we'll say that each of you is only putting out a thousand watts of body heat So now we have eight thousand watts of body heat, plus 2,500 watts of equipment and lights. Total power output: TEN THOUSAND FIVE HUNDRED WATTS. That's toughly equivalent to half a dozen space heaters! Are you getting the picture now? 10,500 watts is 35,000 BTU per hour of heat energy being generated inside the room, AND IT HAS NO PLACE TO GO! It stays inside the room. It cannot leave the room, for the same reasons outlined above. Your small A/C unit that did just fine at 20% capacity with you alone sitting till, won't even make any real difference at all now, even running at 100% capacity: it's just a small 5,000 BTU/HR unit, remember? So even when it is going full bore, 100% duty cycle, there's still another 30,000 BTU/HR left over to deal with! Ouch! Are you starting to see why it doesn't matter where your room is located? It's not the heat OUTSIDE that is the problem. It is the heat INSIDE that is the problem. It does not matter if the temperature outside is -20°F or +120°F. All that changes with that is the initial conditions inside the room, before you shut the doors. After the doors are closed, your room is disconnected from the outside world, and becomes a world of its own. And that "world" has half a dozen heavy duty space heaters inside it, going full bore, which means it gets pretty hot in there, pretty fast. That's the issue that you are missing. If you do not believe me, go to the ASHRAE web site, check the numbers, and check the math. I might have made a mistake, but I don't think so. With 8 musicians, a reasonable set of equipment, and some lights, you'll be pumping out enough heat to keep a three ton HVAC system fully occupied... (One ton of HVAC capacity is 12,000 btu/hr). I'm sure you had no idea things were that serious. Now do you see the reason why HVAC is not a luxury, but a basic necessity? You never had this problem in your old basement before, because you never had it soundproofed and isolated to the level we are taking about before. But you sure will have exactly this problem, with your new room, no matter what part of the planet you build it in. SO, putting in the ventilation system will take out SOME of that heat, but not all of it. Not by any means. To illustrate: Turn on your car heater full blast, and open one of the windows: does the car still get hot inside, even though it is well ventilated? You bet! Very hot, very fast. Even with the ventilation system in your studio running, you STILL need a pretty hefty A/C unit to deal with the rest of the heat, and keep things bearable. Without doing the rest of the math, I would guess that something like a 18,000 btu/hr unit would do the job, or about 1.5 tons. But that leads to another problem: If you put in a single 18,000 BTU/HR unit, then when you are alone in there, making music by yourself, that thing will be on a duty cycle of maybe 4%! It will click on, freeze the room in a few seconds, then click off again for many minutes while the room heats up.... That's bad for you, and bad for the HVAC system as well. It would be better to have two smaller units, say one of 6,000 btu/hr and the other of 12,000 btu/hour, so you can turn the big one off when you are by yourself, and only use it when needed. So that's the problem with heat. Now for humidity. The human body expels about 2 to 4 cups of water per day, just through breathing, plus about twice that through sweating when doing moderate exercise (and even more if it is hot around you.... :) ) So lets be conservative, and say 10 cups per day, or 5 pints. There are eight of you in that room, meaning that there is 40 pints of water per day coming out of you guys, into the air. That's between 1 and 2 pints PER HOUR spraying out into the air in the room. And it has NO PLACE TO GO: Remember? The rooms are sealed with double impermeable barriers.... You HAVE to do something about getting rid of that moisture. The A/C system does that for you: the excess moisture condenses on the radiator fins inside the indoor unit, drips into a collecting pan, and is conducted outside through the drain hose. That's what gets the humidity under control. Without HVAC, you'll have water condensing on all the surfaces of the room, and end up with mold and fungus problems as well. Once again, if you don't want to believe me, check the facts for yourself. I'm not making this stuff up! You can easily find it by Googling it, or just by checking out the ASHRAE website directly. Maybe you think I'm just shooting off my mouth (or keyboard! :) ), and that none of this is important to you, because your room is somehow different from all others, not subject to the laws of physics, but I sure hope that's not the case. Since you don't seem to trust my advice much, I'd suggest that you DON'T listen to me, and rather go out and hire an HVAC expert to look at your situation, and recommended the right solution. That's probably the best advice I can give you on this point anyway: Hire an HVAC consultant to do the math for you, but do make sure that you explain to him that this is a double-insulated, hermetically sealed, soundproof room, not just any old garage or basement.

I want a variable controller to accomodate different situations -- one person vs. 8 people jamming is VERY different.

:shot: :!: :) Yep! See above. As different as 350 BTU is from 36,000 BTU.... :) Or as much as 2 cups of water is different from 40 pints of water...

I think the dead vent design I'm looking at is actually much better at silencing lower frequencies than the typical "silencer boxes" folks are using, with the "muffler" style maze pathway.

:?: :shock: :lol: Well, sorry, but if that's what you think, then you just haven't grasped the principle of operation of silencer boxes that I was trying to get across. I guess maybe I haven't explained it well enough.

Low frequencies just plow right through those little maze barriers.

Ummmm.... no they do not. There are several principles of physics at work inside a silencer, and you are theorizing and speculating without actually understanding those. I have to ask: have you ever built one of these silencers, and listened at the other end: Have you ever spoken to someone who has? If not, then please do: You'll find that in reality they work spectacularly well: far, far better than your theory allows for. To start with, the "maze" is not exactly tiny, and neither are the barriers! Each baffle is a piece of 5/8" or 3/4" plywood, OSB or MDF. That alone, according to Mass Law, is enough to get you about 10 to 20 dB of isolation, per baffle. In fact, this is what mass law says: TL(dB)= 20log(W) + 20log(f) -47.2, where TL is the Transmission Loss across the barrier, W is the surface density of the panel, and f is the frequency. So you can do the math yourself. The empirical overall equation, independent of frequency, for the entire spectrum, is TL = 14.5 log (Ms * 0.205) + 23 dB (where: Ms = Surface Mass in kg/m2 ). So that's the first part. Then, you are assuming that it is the baffles that are stopping the sound: it isn't They do part of the work, sure, but not all of it. There is also the huge impedance mismatch at each end of the box, where cross sectional area changes drastically in a very short distance, plus slight mismatches as the air follows the twisted path inside the box. That can gain you another 5 to 10 dB of TL, just from the air passing from the duct into the box, then back out again, even with no baffles at all! Then there is the issue of attenuation just from the path length. Sound loses intensity due just traveling though air in a straight line (air is viscous), so by creating a long path through the silencer, you can easily knock of another 4 or 5 dB. But then there's the wonderful thing about those baffles; they force the air (and the sound) to NOT go in straight lines, but rather to take multiple twisty turns through the box, and at each turn there are rather large losses in sound. Chalk up another half dozen dB of TL. Finally, there's the issue of damping: The entire inner surface of the silencer is lined with a layer of sound absorbent material, called Duct Liner, which is specially designed to damp resonance within the cavities, and absorb sound along the entire surface area of the duct. So score another few dB of TL from that. (I've been using the term TL, but in reality for an HVAC silencer it should be DIL (Dynamic Insertion Loss). I'm just using TL for clarity.) A good silencer can easily get you 35 to 40 dB of TL (DIL), and a well designed one can achieve over 50 dB. That's better than most studio walls can hope to achieve, and certainly much better than your door is going to get you...

Those seem good for screening out high frequencies,

Ummm.... maybe you should take a look at the DIL tables for good silencers, as published by reputable labs that test these things for manufacturers.... You might be surprised at how well they handle lows.

but without the larger mass of the dead vent, I don't think they will do what I want to do.

I'm not sure where you get the idea that a dead vent has more mass than a comparably size silencer box! In reality, it has LESS mass... Also, you seem to be confused about mass law and isolation: Mass Law is not your friend. Mass alone is pretty lousy at isolating sound, which is why nobody in their right mind builds a studio as a single leaf. As soon as you let go of the idea that mass law is helpful, you'll start understanding that there are better ways of attenuating sound than just simple mass. You need mass, yes, but you need "mass plus something else", not "mass plus mass". If you take a close look at the mass law equation I gave you above, you'll see that in reality if you DOUBLE the mass of a silencer box, it will only get you about 5 to 6 dB of extra DIL, but if you add more baffles to it (without changing the mass), and duct liner, and do the math to figure the impedance losses, you'll find that you can easily get a 12 to 18 dB increase in attenuation, for the SAME mass, simply by doing a more intelligent design, and using the laws of physics in your favor. You might not be aware of this, but the muffler in your car exhaust pipe is a silencer box, based on the above principles. It is not a dead vent. If you want to see just how effective this type of design can be, take out the muffler from your car, and start the engine.... :) (Just make sure you wear ear protection when you do that: it is LOUD!)

I've read several threads on the merits of various designs, and Ted White's dead vent design seems pretty solid to me -- at least in theory.

What DIL does he claim for that design? Take that, and compare it against the numbers for conventional silencer boxes.

the idea of the dead vent is that you use a small section of flex duct inside a giant heavily-drywalled box (outside the studio) filled with insulation,

And the idea of a silencer box is that you use a large cross section of duct inside a giant heavily-drywalled box. Large cross section means much lower air velocity, which means much greater attenuation due to impedance mismatching, and much lower self-noise. There is no impedance mismatch in a dead vent: the duct is all the same diameter.... So there is no change in velocity. The laws of physics dictate that it therefore CANNOT be as effective as a silencer box of the same size and mass, since it is NOT using one of the key principles that silencer boxes use to achieve very high levels of attenuation.

and the variable path of the flex duct sends the low and high frequencies into the insulation and double-drywall layers of the surrounding box.

The path isn't variable: it is fixed! It would only be variable if there were something that changed the path over time, to make it longer or shorter, or adjust the curvature. It is a fixed path that happens to be slightly curved. Very slightly. On the other hand, the path through a silencer box is massively curved: there are multiple 90° bends along the way. Are you trying to say that driving through a mild left-then-right curve robs MORE power from your car, than steering it through half a dozen very tight hair-pin bends? :) I don't think so...

the flex duct sends the low and high frequencies into the insulation and double-drywall layers of the surrounding box.

I'd be really keen on seeing the theory of how thin metalized plastic foil is able to accomplish that better that the massive, thick pieces of plywood inside a silencer box! :) On the one hand you are claiming that the thin foil walls of flex duct somehow magically have more of an effect on low frequency sound waves than 3/4" planks of plywood, with an inch of duct liner on each side.... And you are also trying to say that the light fluffy insulation around the duct somehow manages to magically attenuate sound that is passing along the duct? Add that this effect is greater than the effect of masses of plywood and inches of duct liner?

I'd prefer to attenuate most of the sound BEFORE it gets to the outside duct run, because that's in an un-soundproofed area.

Right. Then put the silencer inside the room, or inside the wall cavity, where it can act on the sound as it passes through the leaf, which is the best place to do that.

(I know people hate the term "soundproof", but you get my meaning).

:thu:

Anyways, I'd love to follow your advice about doing the math to calculate the fan & duct size perfectly, but the truth is that I really don't understand it well enough myself to do that. And it's not important enough to me to have a totally quiet system

The math I was talking about isn't related to keeping things quiet: it is related to keeping you alive inside the room, and keeping the conditions inside liveable. I was talking more about the heat, humidity, oxygen, CO2, and ventilation levels. Those are the things that you can't afford to NOT calculate, regardless of whether or not you want a screaming hurricane or a silent whisper as the air comes out the register.

And it's not important enough to me to have a totally quiet system (inside the rehearsal room, that is) for me to pay a lot to a professional HVAC person.

How important is it to you to stay alive in there? :) A normal person inhales and exhales about 11,000 liters of air per day. About 20% of that is oxygen when it goes in to your lungs, and only 15% as it comes out: meaning you use up about 550 liters of oxygen per day, or about 23 liters per hour. So you need a dozen very large coke bottles full of oxygen for each person, each hour. Eight people in the room means that you need to supply a hundred large coke bottles of oxygen per hour to keep you guys alive in there.... And you also need to remove another hundred large coke bottles of CO2, every hour.... But your room is surrounded by two impenetrable air-tight barriers.... So getting the ventilation right suddenly seems like it might be a "life or death" sort of thing (very literally!), and maybe worth spending some money on! :)

All I really want is a variable system that can do a LOT of airflow,

Once again, that's a bad idea. It must never be capable of doing substantially more air flow than is needed at maximum occupancy. Since ventilation is the ONLY thing that connects the inside of your room with the outside word, it can directly affect the climate that you are trying to establish inside the room. And it also means that the outside conditions now ARE relevant for the inside of the room, to a certain extent. That data I just looked up for SFO tells me that relative humidity can ranges from around 50% to 90%, averaging around 75%, year round (proximity to the ocean). Ideally, you want about 45% inside your studio. So if you suddenly start pumping in massive amounts of outside air with 95% humidity, you greatly overload the ability of the A/C system to remove that humidity from the air, and once again end up with water running down the walls. But now you just added another problem with your oversize fan: latent heat. Since most of the capacity of the A/C system is now just simply removing water from the air, there is not any left over to cool the air, so once again, it starts getting hot in there, even though you are pumping in cool moist air! Bet you never expected that.... Ain't HVAC a bitch? In other words, by pumping too MUCH cool moist air into the room, you can actually make it hotter inside, since the HVAC cannot remove the latent heat of condensation fast enough and also cope with the plain temperature issue. So you'd need a larger HVAC system, which costs more to buy, and costs more to run.... So you do NOT want a ventilation system that can do a lot of air flow: you want one that can do just the right amount of air flow, no more and no less. Also, if you have an oversize fan motor that you are always running at minimum speed, you are wasting a lot of energy: neither the motor nor the blades are moving at the most efficient speeds that they were designed for. So you are wasting power, and your electricity bills will be higher than they need to be. I though living in California was all about being green and efficient, saving energy, etc? :)

but honestly I'm not sure if I can afford it or learn how to calculate for it.

After reading all the above (assuming that you did!), can you afford to NOT calculate it? Rod explains the basics fairly simply in his book. Or an HVAC contractor can do all the figuring for you.

I am confident this will work

I'm not! :) I'd only be confident if you did the math and showed me where I went wrong above...

I hope I don't sound dismissive here;

Not at all! I get it: you don't really know how to do the math, because you haven't looked into it much, since you don't see the need for it. That's OK, and when I first approached this subject I though the exact same way you do. I didn't see the need for fancy HVAC systems in a simple home studio. Until I looked into it, and started learning just how gravely important it is. Hopefully, I have helped to change your mind on that issue. :)

but for my purposes I'm not sure if I can afford / understand how to follow your lead. Does that make sense?

Well, it makes sense from the grammatical and linguistic and economic points of view, but not so much from the logical and acoustic and "staying alive inside my room" points of view. :)

The main takeaway for me was that the silencer boxes create an impedance change based on the diameter of airflow area -- which the dead vent doesn't do.

Yup! :) Among several other things that the dead-vent doesn't do.

However, the dead vent does disperse the sound through the thin membrane of the flex duct,

And why would that be a GOOD thing? :shock: Low frequency sound that gets through the membrane then goes straight through the fluffy insulation, and hits the wall of the box.... How is that a good thing? How is that better than what a silencer does, by placing sold, massive, damped barriers directly in the path of the sound, to PREVENT the waves from reaching the wall of the box?

We beefed up the area between joists with one layer of 5/8" quietrock (found on super-discount, used, for $7 a sheet) -- greenglued to the wood above,

I sure hip you nailed it too, or used cleats, not just the Green Glue! :shock: Green Glue is NOT an adhesive, and cannot be used to "glue" anything to anything. Even if it were glue, you still need to hold the drywall in place, mechanically. Gluing one layer to another is illegal: it will not pass code or inspection. I'm looking at that photo with a very scary feeling, since I don't see any cleats, and I don't see any nail heads. Was that inspected? I find it hard to believe, that an inspector would sign off on that?

we had to frame it, then take off the plate bolt nuts and tilt it over, then put the plywood and two layers of 5/8" drywall (with GG sandwiched). It went back up without a hitch

Why not just built it the normal way? Build it flat on the floor, framing, plywood, drywall and all, then tilt it up? Why did you need to build it standing up, then lay it down, then lift it up again? Seems like wasted time and effort to me. I also don't see any insulation in that cavity.... How are you going to get the insulation in there afterwards? 6" isn't enough to do that. Are you planning to lay the walls down again, put in the insulation, then stand them up again? Also, I don't know if the outer leaf visible in those photos is the outside wall of the building, but if it is then I'm wondering where the vapor barrier is. Big issue.

Next we have to build a little mini wall above it, to finish the connection all the way up to the ceiling.

:shock: :!: Whooaaa! What "connection to the ceiling"??? There cannot be any "connection to the ceiling"!! The inner leaf CANNOT under any circumstances, touch ANY part of the outer leaf. Not even a single nail. The two levees must be totally independent, no connections at all. Any connection is a flanking path, which destroys your isolation. The inner leaf, when completed, is a self-supporting structure, just like the outer leaf. The two cannot touch: that is the entire point of building a two-leaf system for isolation: the leaves are fully decoupled, no contact. If there is any contact at all between them, then you might as well have not bothered, since you lose all the benefit. So that "little mini wall " has to come out, and you need to check your entire plan to figure out what went wrong! It might just be the lighting, but to me it looks like there is only one top plate on that wall segment: there should be two top plates. One alone is not enough to support the weight of the ceiling properly.

There are some annoying duct runs and water pipes that have to be built around a little bit up there, but it's mostly pretty clean.

It looks like there is enough space to interleave the new ceiling joists between the existing ones: That's good! You don't have to lose so much ceiling height like that. --- I sure hope I haven't totally bummed you out, and put you off studio building forever! This is all meant to be constructive advice, trying to help you do it right. As you might have guessed, diplomacy is not one of mys strong points.... I tend to just call it like I see it, and blurt it right out, no beating around the bush.... I guess that's why I never did get appointed as ambassador to another country.... :) - Stuart -

Thanks again for the reply. I'm not looking for diplomacy, I'm looking for good info, so I appreciate your taking the time to spell it out. I think I get it now about the silencer boxes; I thought they had a good M-A-M system, but upon looking closer it looks like it's more just A-MM -- which is not what we want, I realize. So I'm convinced. On A/C I'm still not convinced, you'll have to forgive me. I'm not trying to be stubborn or difficult, but I just know my experience in this area: I have never ever used A/C in a car, or in a house. You said "open the windows in a car and it's still hot" -- not here. The reason why living in SF DOES matter is that if you move enough outside air indoors, you circulate out any heat. Simple. Yes, humidity is still a bit of a problem, but most old houses around here are so drafty that the inside humidity is about the same as the outside -- and they don't seem to have any problems. You mentioned the lack of vapor barrier -- yep, it's a house built in 1904, so there's no vapor barrier. No problems, either. If I was housing a lot of expensive recording equipment, I would do A/C -- that stuff is too valuable to mess with possible humidity problems. But as long as I have enough air circulation, going inside and out, I think I don't need A/C. Don't mean to :horse: too much... On the other points: don't worry, I'm not really "green gluing" anything -- I'm quite aware it's not a glue. All drywall is screwed in properly. And the reason the wall was constructed at that angle is because there is a giant post holding up the house, which prevents the wall from laying down flat on the ground. By the way, that tilt-up wall is an OUTER leaf -- and yes, I know that means I will have triple leaf. I'm aware, and willing to risk it. With three 5/8" layers on both inner and outer walls, I'm hoping to attenuate most sound before it gets near that outer leaf (which is indeed the house walls). The reason there is no top plate is that it isn't actually the top of the wall -- the mini-wall above is going to meet it. It is an outer wall, therefore it needs to go all the way up to the ceiling. I'm actually not going to interleave the new ceiling joists, because the beam going through the middle of the room makes that direction too difficult for joist runs. I'm running joists perpendicular to the existing joists. But I will still have just under 8' of ceiling height. Thanks again for the feedback. I'm happy to have switched to a silencer box design, though it looks like it will take a lot of work. But the math of calculating static load, including calculations for the silencer box, duct liner, duct size, run lengths, turn angles --- it just sounds like too much for an amateur like me to handle. You wrote earlier: "If your flow speeds or flow volumes are too high, then you crate air noise and the movement of air through the room will be noticeable: you will feel the wind blowing through the room." -- that sounds great to me, I'm a drummer!!! - Flaco

Hi. Quick question about screwing in hinges for the super door. So I have Rod's book, I know I need 5/4 pine jambs and serious ball-bearing hinges. And I know I am supposed to screw in those hinges with 3" or 4" screws, so they go all the way through the jamb to the framing, right? But look at the attached picture, where the yellow is the hinge, and the red is teh screw -- it's going to go right into drywall, not into framing, because the 2 or 3 layers of drywall eat up 1-1.5" of space on the outside of the framing. What am I missing here? - Flaco

New updates. A lot has gotten done in the past two weeks. Framing is finished and 2 layers of drywall with GG are on the outside shell. Basic wiring is run. Pix show the progress. Next steps: after finishing the fire stops with mineral wool packed to 30-40% and fire caulk, and then putting in insulation and making sure all the acoustic caulking is finished nicely, we'll put up OSB on all the interior walls (caulking all perimeters when we add it), then add double drywall with GG, caulking all perimeters according to Rod's suggestions. We also need to frame out the columns that will get double-drywall around the two big posts in the middle of the room. Obviously that framing will be hanging from the new joists, not touching any of the original house members. As far as electric, I'm going to go with surface-mounted electric boxes so I can have very small penetrations just for the romex. I still have a question regarding drilling in the hinges -- see my previous post. If it's fine to just go into the 5/4 stock and nothing else, then I'll leave it at that. But since everyone seems to say hinges need to be drilled in with 3 or 4 screws, and I just don't understand: drilled into WHAT? Anyways, I've decided to do 12" lined ducts, thanks to soundman and others for helping educate me and push me in this direction. I've still got those possibly-oversized fans (three hundred something CFM each), which are sized at 6", but my reading up on the topic has shown me that I can transition to 12" duct immediately on both sides of the fans, and still have very effective low-sound airflow in my situation. I don't have any plans for AC. One question about the silencer boxes: are there any drawings out there for showing how to cut through the wall to do the silencer box on the OUTSIDE of my studio room? I realize that penetrating the double wall is dangerous business, so I want to check to see if this is possible. I have lots of space outside of the room, and I'd prefer not to give up any space inside the room if I can avoid it. Can I build a double-drywall passageway in between the two walls, careful not to directly connect the walls to each other (leave a little space for caulking so I don't create flanking issues), and then build my silencer box outside my isolation room? I have Rod's drawings for making the silencer box, but they appear to be designed for INSIDE the noisy room. Also: how many turns are good for my duct runs? I could do straight runs (the distance is about 25'), but if it's better for sound attenuation I can put in some jogs or turns. Thoughts? Or any comments about what you see in the photos? As you can see I didn't do the conventional "tuck the joists up in between existing joists" method, because of that pesky beam running down the middle of the room. But this way I don't have to build weird framing around the beam, or a soffit for it, and I still will have 7'10" of height or so when the room is finished. - Flaco

I've found a good local supplier of 1" sheets of Johns Manville super duct. It looks a little tricky to do DIY, but I looked at the Manville specs for installation, and I think I could handle it. Also, I'm considering doing part of it galvanized. Actually the main reason to do galvanized for part is that I have a section of duct that is going to be under an overhanging roof, but semi-exposed the temperate climate here. It won't get any actual rain, but here in San Francisco the fog can be so thick that it coats everything, so I am figuring I need to keep the duct board out of that area. In the basement the humidity is totally under control, so I'm thinking I will use duct board until I penetrate the side of the house, then galvanized for the rest. Seems like I have answered my own question here, but I'm open to suggestions. I like the fact that I could avoid possibly toxic duct liner by using the duct board for part of the run. And at $8 a linear foot of 12" square duct using duct board, it may be competitively priced with 12" galvanized. Thoughts? - Flaco

and I think I could handle it. Also, I'm considering doing part of it galvanized.

Great! But even galvanized ducts need to be lined inside, for best sound reduction and also for thermal isolation....

like the fact that I could avoid possibly toxic duct liner

Why do you want ot use "toxic duct liner"? :shock: :?: :!: Just use normal duct liner that is specifically designed for use inside HVAC ducts, and is not toxic at all! What type were you planning to use that is toxic? The type of duct insulation that wrap around the OUTSIDE of HVAC ducts is not the right stuff to use INSIDE the duct. for many reasons. Whatever you put inside your ducts must be proper "duct liner", meant specifically for that purpose. - Stuart -