Synyrgy Cynyma ( Pronounced: Lynyrd Skynyrd )

Discussion in 'Listening Room / Home Theater Build Projects' started by 1_sufferin_mind, Sep 25, 2018.

  1. 1_sufferin_mind

    1_sufferin_mind Active Member
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    So you thought you'd never hear from me again? Well, I'm back in full character with a vengeance! It's good to see some old faces, and good to know there are plenty of new ones around to carry the torch.

    I'm finally making good on a promise--or threat, if you prefer--to graduate from my smallish 10x13 HT to much more serviceable new construction. The need to care for an elderly parent has started the ball rolling to add a second story onto our existing home. And since I'm familiar with how useful and creative AV NIRVANA members can be, I thought I'd give those interested a shot at spending my money for me! We don't even have a floor plan yet, so my mind is an open slate. I do know that the new HT room will be upstairs and that I would like to have a separate equipment/media storage room. Also, HVAC noise control and some level of sound containment would be nice. I'll be using all my existing gear, though I may need to add a sub to help smooth-out bass response.

    I'm obviously going to have a lot of questions, as I've never done this before. And because I'm not handy with tools or construction, I think it's going to cost more than it would for most of you DIY'ers. So where do you think I should start? Room dimensions/materials planning? Consultation with a builder?

    Questions/Comments welcome!
    Thanks (as usual) for putting up with my ramblings, and thanks in advance for your enthusiastic participation!!
     
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  2. 1_sufferin_mind

    1_sufferin_mind Active Member
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    Hmmm... Maybe I'm not asking the right questions, or am not being specific enough. Sorry if I said anything offensive. It's not my avatar, is it?
     
  3. Sonnie

    Sonnie Senior Admin
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    No doubt we lack folks to drive the discussions like we had over at HTS.

    I think with what you are doing you would surely start with a contractor... but one of the biggest things that would concern me is noise traveling down to the rooms below the theater room. I would be looking at ways to isolate the sound, construction methods, sound barriers, etc. As well as considering the same for your walls.

    Of course planning out the best size is another important part... making sure you don't have too many null spots around the main listening position due to room dimensions.
     
  4. 1_sufferin_mind

    1_sufferin_mind Active Member
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    Hi Sonnie! I didn’t expect one of the big guns so soon. Thanks for your answer.

    I was afraid that disturbing downstairs neighbors would be an issue, especially for bass. I’ve read that good construction and special materials are key to successful soundproofing, so it’s necessarily expensive. But it can also introduce acoustic issues of its own when taken to extremes. Again, just paraphrasing some posts I’ve read.

    I’ve also read several build threads and was impressed with the materials and construction knowledge. It takes a lot of time to explain the minutiae of a design, so I totally understand why they’re usually omitted. Or maybe it’s just that they’ve been doing it for so long they take it for granted that we’re following along without trouble.

    How do you know when to use 3/8 vs 3/4” wallboard? How do you know when to use wallboard vs Sheetrock? Are they the same?
    Is there a case where you would not want to use green glue between layers? These are some of the questions I’ll be looking into.
     
  5. Matthew J Poes

    Matthew J Poes Staff Writer
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    I can help with the sound isolation when the time comes. I’ll just mention that some of what you’ve said is more myth than reality and comes from what I think was an oversimplified assertion by Floyd Toole then misunderstood by forum users. That is, sound isolation makes bass worse.

    It is in fact true that a solid and rigid wall of high density is more reflective to lower frequencies. What is not true is that this is so for typical sound isolation techniques used for home theaters at what we define as low frequencies. That is because we actually use walls which are articulated and damped so that they move with the low frequencies, and to damp modes produced in the walls. The walls are more massive, but when a decoupled wall system is used, it actually turns the wall into a bass absorber, not reflector. The wall will be more reflective at midbass frequencies, but at these frequencies we can use bass traps to treat the room.

    Now keep in mind, providing sound isolation of low frequencies through the floors is a major ordeal. You need to follow the “room within a room” approach to an extreme. Your floor must be highly decoupled with a large airspace from the joists. The joists should ideally be insulated. The ceiling in the room below itself should be decoupled, damped, and double or triple layer.

    I can show you a few different assembly schematics and the mind of isolation they provide. Just keep in mind that none are very effective at low frequencies. The only true way to isolate at low frequencies is possibly out of your budget. Basically you install spring isolators for slabs onto a double thickness deck. You then poor specially damped sound isolation cement to roughly 2” thick or more. On top of that goes a number of layers of resilient damping products until you finally get to the floor itself. Including the air gaps you can end up with a 6” thick floor assembly on top of the decking itself.

    As you can imagine the weight is significant and easily exceeds normal joist capacity so you need it to be an engineered solution. I’ve never had the joy of a residential property request it, so I am not totally sure what is used to ensure the floor will not collapse. My guess is engineered joists and possibly more support beams. Kinetic and Maxxon makes the products I would use for this if you want to explore. They also have lesser products that may be more affordable and doable in a residential setting with sound isolation data available upon request.

    I also have some design ideas that I’ve wanted to try sometimes for improving Lf isolation between floors. Some building methods I suspect would improve Lf isolation better without quite as much weight.

    Another thing to keep in mind, the airgap effectively extends the point at which mass dominates sound isolation. Larger airgaps extend the mass controlled zone. Since stiffness dominates below this and the creation of a “stiff” structure is actually harder than it seems (think ribbed plate steel, not stud wall), this is a good thing to focus on.

    With most of the domestic options that I would consider doable in a residential space, sound isolation below 80hz is only slightly better, maybe about 3-6 dB, than traditional construction. To go from 6dB to something more like 12 or 20 or 50dB becomes exponentially more expensive.
     
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  6. Matthew J Poes

    Matthew J Poes Staff Writer
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    On the HVAC front, that too gets really expensive, but once you understand the fundamentals and avoid short cuts, it can be managed. Being totally honest, the cheapest solution for HVAC is a split system in the room. If you need heat and live in a cold environment, you might need to add radiant heat as well. The problem with this solution is that the best of them are still noisy and will set your rooms noise floor.

    Another option is to use deadvents. If you have a buffer space to push and pull air from, this can work ok. I’ve had mixed luck with this. Sometimes it works brilliantly, other times it doesn’t.

    Next cheapest is actually likely a separate system. At least around here you can have a full furnace and AC unit installed for about $5000-$6000. If it’s new construction then the only other differences are slight.

    The most expensive is the solution I did, and I took short cuts causing it to not work as intended. I attempted to isolate the system from the main system using acoustically designed expansion boxes, mufflers, acoustically lined ducts, acoustic end boxes, etc. My short cut was undersized and under-engineered mufflers and expansion boxes. It allowed sound to still travel to other rooms. It is clearly working, but if I’m getting 50dB of sound isolation and sound is 105+dB, then that is still a very audible 55+ dB. That is my problem.

    I would avoid using flex duct unless you can put it in a sound isolated space. For my space, flex duct would be in the walls or ceiling. The breakout noise of flex duct is very high and so it’s like cutting a hole in my wall or ceiling. That’s how flex duct should be treated, if cutting a hole directly in your wall or ceiling would be a problem, don’t use it.
     
  7. Sonnie

    Sonnie Senior Admin
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    My application might be similar to what Matt is saying on the bass absorption. I have a walkway/hallway between my room and our house... a back door entrance where we walk in and the theater room is on the left and the house on the right. Pics via the link in my sig might help give you a visual. For that theater wall on the left I used 6" top and bottom plates with 2x4 stagger studs... basically a 2x4 every 8" but staggered on each side of the 6" plate. The wall boards on each side are decoupled except for a few inches at the top and bottom where the 6" plates connect the two sides... so with double plates, 3" at the top and bottom (6" total). I installed 2 sheets of 5/8" firewall/drywall/sheetrock on the house side of the staggered stud wall... with caulking between the two sheets. I blew in newspaper insulation (very thick stuff) into the walls. This stuff is amazing, because 3-4 years later I had to take out the inside part of one of the outside walls where we blew it in and it was aggravating to remove... had not settled any at all... not even 1/16". To finish the interior wall, I installed 3/4" plywood, then green glue (not sure if it was needed, just did it anyway), then a 5/8" sheet of drywall. The other three walls are on the exterior of the house... which are double-walled, blown... plywood/drywall. I still had the issue of the ceiling and needed to isolate the sound from traveling thru the ceiling into the attic and into the rest of the house. I already had 1/2" drywall on the ceiling... so after adding significant bracing in the attic to keep the ceiling from falling on my noggin, I added 3/4" plywood, green glue, then 5/8" drywall... then blown insulation on top in the attic. The only real serious leak is the return air and ac vents, but it is a standalone unit for the theater room only, so the duct work does not travel into the house. The entrance is two solid-core wood doors where I have to lean up against the second door to get it to shut because it's that tight with the air being trapped between the two doors when shutting it.

    So... what do I get for this? If I play Cloverfield at deafening levels in the theater room (back when I had eight (8) x 18" subs powered with about 8,000 watts... it sounded like faint thunder off in the distance when in the house. However, in most instances, you can't ever hear a thing inside the house... at regular listening levels, which when watching a good action movie with a lot of bass, can get pretty loud. I achieved my goal with what I did. I have no idea if I could have gotten away with less... possibly... but we'll likely never know.

    I don't have any issues inside the room... and we've done all kinds of testing in here. We've used this room for 4-5 speaker evaluation events and several reviews... and literally tested the daylights out of it for reflections, etc. It's far superior to most anything else I've heard anywhere thus far... and I've heard quite a few systems in a vast variety of room setups. And yes... I am bragging about it, because it truly is what it is. :bigsmile:
     
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  8. Matthew J Poes

    Matthew J Poes Staff Writer
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    Sonnie, I’ve long suspected that your particular setup uniquely allows much higher than normal isolation to the main house. Which is great for you. That corridor between the theater and main house is a huge buffer.

    When a space more directly adjoins a livable space I think it’s much harder to achieve that same level of isolation. Of course, you also did an exceptional design isolating it.

    As for green glue, I think it’s worth it. It doesn’t offer a ton of extra sound isolation at the peaks of the TL curve, but it does reduce the effect of the coincidence dip. That makes a pretty big difference. Without the damping, the resonant dip transmits sound as if there is no barrier at all. It also adds damping with the walls which had acoustic benefit. I think it’s been under-appreciated for this.

    I also think you used a building technique which I believe can slightly impact sound isolation in a way that benefited your particular setup, but otherwise might not have been ideal. Typically sound isolation in the mass controlled region is negatively effected by high wall stiffness. A floppy well damped wall is generally better. However, both above and below the mass controlled region is a stiffness controlled region. Plywood and OSB is much stiffer and more poorly damped than drywall. Normally it’s preferable to avoid using a layer of this if designing a room to maximize transmission loss in the mass controlled region. However, it has a big advantage in that stiffness controlled region. If you can damp it well (which GG does) then it increases LF TL a decent amount.

    It’s one of my design “tricks” for designing a room for maximum LF TL. I make the inner shell floppy and well damped, on springs. I make the outer shell stiff and rigid but well damped. I also use a higher density insulation in the walls. This is pretty similar to what you did.

    The method I’ve been wanting to try uses MLV as well. Fastened to the studs but behind the hat channel is a layer of 2lb density MLV on both receiver and source side. Similar approach with the floor.
     
  9. 1_sufferin_mind

    1_sufferin_mind Active Member
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    No doubt you can help, especially considering the expertise you've communicated so far! I believe I'll need to temper the complexity and cost, so will necessarily wind up with less than optimal results. Perhaps far less than optimal, but at least some isolation will be in play. I suspect I'll need to adjust my late-night listening/viewing habits. Maybe I can use this as an excuse to tread the waters of the headphone scene!!

    Thank you for the clarification. My traps are ready, but will probably need more for the bigger room.
     
    #9 1_sufferin_mind, Nov 8, 2018 at 10:19 AM
    Last edited: Nov 8, 2018 at 10:25 AM
  10. 1_sufferin_mind

    1_sufferin_mind Active Member
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    Yup, I was afraid of that. I was initially concerned about HVAC noise getting into the room, but you raise an excellent point regarding sound leakage, too.

    The house currently uses flex duct in the attic, because it's on a slab. That's not to say the upper floor couldn't be configured differently.
     
  11. Matthew J Poes

    Matthew J Poes Staff Writer
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    Flex duct isn’t the end of the world if it is completely in an insulated attic. I’m this case the sound does escape into the attic space but the insulation absorbs a lot of it. It probably doesn’t work as well for low frequencies. I’m personally not a fan, but I’ll admit many have done this and been happy. You would just want to use acoustic flex duct to help absorb some of the sound that transmits through the duct.
     
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  12. Matthew J Poes

    Matthew J Poes Staff Writer
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    Well there may be tricks and cheaper solutions that you could try. The use of resilient channel or better yet, clips and hat channel makes a big difference in sound isolation. Among the biggest improvement in fact. Two layers of drywall adds mass and that is goood. Green glue is good, I think it’s needed, but it cost is a concern, it’s the first thing I would dump. I’ve been looking for a cheaper alternative, but unfortunately there isn’t one. There are some special damping adhesives made for the industrial market that I had hoped would be cheaper, but even in massive bulk they cost as much or more than GreenGlue.

    Getting massive amounts of isolation is expensive. However, you can make great strides and achieve a room that’s really good for not a lot of money. You just have t understand where to put that money.

    I recently read about a home theater that had such good sound isolation that the noise floor not only fell below the measurement limits of an ultra-low noise mic, but was at or below the audibility threshold of a human. I can tell you that to replicate that level of quiet takes serious engineering. I wouldn’t even take on a job with that requirement, the liability is too high that I would fail. I could only imagine that it would cost upwards of a million dollars to achieve that in a single room. I say that to give scale to what it takes to achieve a room so soundproof that a reference level movie is not heard or felt in other rooms at all. The cheaper solution would be to either do what Sonnie did and convert a garage so it’s detached, or build a man cave in the backyard.
     
  13. bkeeler10

    bkeeler10 Active Member

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    I just saw this thread today. I am at the tail end of construction on my dedicated theater, and can offer some insight. I will say that this soundproofing business is expensive. Also, one thing I had not anticipated was the compromises I had to make. My theater is part of an add-on to my existing house. Thus, there were limitations beyond my control within any sort of reasonable financial limits. Some examples:

    1. The HVAC supply lines for the space above the theater had to go in the ceiling cavity of the theater.
    2. I was unable to use lined duct for the HVAC supply and return lines to the theater due to space constraints in the ceiling along the pathway they had to travel.
    4. While most of the theater has double sheetrock, there are a couple of small areas where it could not be done because of space constraints related to doors and doorways.
    3. The theater sheetrock was installed in such a way as to make it difficult to seal it up around the perimeter.

    These were all unexpected and unpreventable without spending a fortune to change things. There were others that were oversights on my part that could have been better if I were paying attention and/or had more experience. To do this right in an add-on is more difficult and more prone to unexpected circumstances. It would be much easier with new construction, but even then, experience and close attention to detail in the design phase is important in order to avoid pitfalls that will compromise your solution.

    When I get a minute, I could put together a list of things that might help in the process. I also have access to modeling software for sound isolation. Combined with Matt's expertise and experience, maybe we can get you to the best affordable solution.
     
  14. 1_sufferin_mind

    1_sufferin_mind Active Member
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    Thank you both for your detailed thoughts. Rather than sling vague ones back at you, I feel the need to research a bit more. I believe that approach will help produce an intelligent exchange. :)
     
  15. 1_sufferin_mind

    1_sufferin_mind Active Member
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    Agreed, considering my implementation will be funded by a "working man's" budget, lol. I intend to keep my solution in the realm of sound reduction, rather than true sound proofing. Whatever the term used, I found out that controlling sound leakage either into or out of the theater is generally facilitated using the four-stage process shown below. After some research, I'm still unclear regarding the differences between resilient channels and hat channels, but know that the latter are recommended for demanding applications such as Home Theater isolation.
    1. Decouple
      Soundproof 01.JPG

    2. Absorb
      Use sound-absorptive materials such as cellulose, mineral wool, and recycled cotton (R13 in walls; R19 in ceiling/floor). The key is to keep the density low. Don’t compress or pack the insulation. There is no data that supports that any other insulation (including the “acoustic” labeled, and recycled cotton) works better. Also, foam (open or closed cell) is superior for thermal but distinctly worse for acoustic. Use the cheapest fiberglass you can find.

    3. Add Mass
      Use dense/heavy materials such as Drywall, Plywood, OSB, and Cement Board. For sound to conduct through a wall, it has to actually move the wall ever so slightly . A heavy wall is harder to move than a lighter wall, but it will still vibrate (i.e. it will still let some sound through). It is best to use two layers of 5/8″ drywall, but simply adding mass does not help block much bass.

      [​IMG]

    4. Dampen
      Reducing the drywall from vibrating in the first place would make the jobs of the mass, insulation and decoupling easier. This is where Green Glue sandwiched between layers of drywall helps to keep it from vibrating excessively.

      [​IMG]


      [​IMG]
     
    #15 1_sufferin_mind, Nov 12, 2018 at 8:48 AM
    Last edited: Nov 12, 2018 at 9:23 AM
  16. 1_sufferin_mind

    1_sufferin_mind Active Member
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    The following discussion assumes I'm able to afford the chosen construction techniques and materials. It's entirely possible I may change them after reviewing cost quotes. I currently have only a vague budget of $125k in mind for construction of the entire upstairs. My gut feeling is that will fall dismally short of what I'd like to accomplish with the new theater. I believe I'll spend more on its acoustic performance than on its aesthetics.

    Requirements for the upstairs floor plan are limited only by a master bedroom, walk-in closets and master bath. Other than a possible guest bedroom or den, the remaining floor space (~1600 sq. ft.) is available for the theater room. So my current plan for the new upstairs construction is to locate the room as far away from the downstairs bedrooms as possible. Luckily, both of those will be on the same side of the house. That may not help much as far as bass is concerned, but the inverse square law for sound intensity works hand-in-hand with soundproofing techniques for mid-to-high frequencies. I also intend to treat all four walls - rather than target just the main leakage pathways - using double-studded and insulated, green-glue walls with a sufficient air gap. The upstairs floor / downstairs ceiling will have its own issues (as discussed here). I'm unsure which flooring system (floating joist vs clip/hat) would be better for my situation.

    [​IMG] [​IMG]

    [​IMG]

    Soundproofing techniques obviously need to be considered before construction begins. Actual size and usable size differ because of room-within-a-room and double-wall construction. I would think that particulars of screen size, viewing distance, and seating arrangements should be specified first. Once the functional floor space has been defined, it will need to be expanded to accommodate decoupled/damped walls. My research shows that more mass is only effective up to a point. Adding dead airspace can be even more beneficial, but necessarily consumes real-estate. The triple-leaf effect described here concludes larger air gaps between studded walls improve low-frequency isolation by lowering the wall's resonance. How much dead-air space is realistic before the outer shell becomes exceedingly large?

    I think the last soundproofing technique I'll need to employ is known as "flanking." This resource shows how to improve sound isolation even further by paying attention to leakage through doors, windows, HVAC vents, fixtures, etc. Addressing such issues seems beneficial to my circumstances, but I don't believe incorporating a floating ceiling will significantly help sound isolation between the theater room and first floor rooms. Thoughts?
     
  17. 1_sufferin_mind

    1_sufferin_mind Active Member
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    Your insights are a welcome addition to my growing arsenal of HT construction tips! It's becoming obvious to me that I'll need to make compromises to reach a final solution. I may not be able to implement a particular construction technique because of expense/difficulty of execution.

    What were the pros/cons of being forced to run the HVAC lines above the theater (attic?) versus being able to run them in the floor.

    The learning curve does not seem intimidating so far. You must have experienced some frustration when seeing your research and planning so frequently uprooted! It sounds like you still have unresolved sound leakage issues (i.e. flanking), some of which are caused by existing construction limitations. I gather from your own theater build that you have yet to install/audition audio equipment. I'm interested to find out how you'll approach identifying and resolving flanking noise.
     
  18. 1_sufferin_mind

    1_sufferin_mind Active Member
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    I'm starting to see why soundproofing quickly escalates up the cost scale. But even if budgetary constraints were relaxed, would it be worth pricing the house out of the neighborhood with an expensive HT room? More and more I get the feeling that the compromises I'll need to make with soundproofing will involve a change in viewing habits that include lower volumes during late-night sessions.
     
  19. Matthew J Poes

    Matthew J Poes Staff Writer
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    If this helps, my experience (which is still relatively narrow in terms of number of total quotes I've seen for different jobs, and restricted to the Chicago Burbs) is that you should expect to pay about $20,000 to $40,000 extra to soundproof a theater. It could be less if you used lesser methods, had a contractor that gave you better pricing, or reduced material costs.

    I haven't looked in over a year, but as I recall, extra costs for mine were something like this:
    • ~$3000 extra in drywall (one layer 1/2" vs two layers 5/8"
    • $500 for 3/4" drywall used in a few locations, custom ordered
    • $600 for 300xDirect Mount Furring Clips
    • $500 for 100xresilient Mount furring Clip
    • $2250 on 50xSpring Isolator Clips (used to decouple the ceiling and headers from the rest, can be replaced with cheaper resilient mount clips)
    • $500 in extra 2x4 lumber
    • $1250 for 5 buckets (5 gallons) of Green Glue
    • $350 for 40 tubes of acoustic Caulk
    • $600 for 2 solid core doors, specially ordered with slightly higher STC ratings than normal (30's for one and 40's for the other I think, can't recall)
    • $300 for door gasketing for two doors
    • $1000 for Acoustic floor underlay
    • $2000 for Mineral wool insulation (I used pretty standard stuff, the higher density stuff was used in select locations, but had I used AFB everywhere, it would have been more than 2 times that price in just insulation)
    • $1000 for 2x HVAC Mufflers
    • $500 for 2x custom expansion boxes
    • $1600 for Acoustic Duct Liner and Duct Damping treatment spray
    • $250 in Hat Channel roughly
    • Extra labor costs, not sure what it came to, but it added days of extra work that I had to pay for, I am sure it was $1000's of dollars
    I bought everything with commercial business accounts and got discounts across the board. Those are rounded numbers and some may be off, I don't have my speadsheet on this laptop to check anymore. I know my Wife is quite insistent that we spent an extra $20,000 on soundproofing.

    In any case, many things I did above you don't need to do to get really good soundproofing. What I did above is also seriously compromised over what you would do in an ideal setup. Those spring isolators are $30-$50 each and you need a lot of them. I also didn't do a sprung isolated floor, too costly ($5000 or so). My system should have used a lot more spring isolators to really get better LF decoupling, but it was just too expensive for a small overall gain. You can really see why this can cost so much though. It all adds up quick. Those $3 clips get expensive when you need 200-300 of them. Those $40 clips get expensive when you need 50 of them.

    I probably used twice as much acoustic caulk as was needed, I had a bucket and a half of green glue left over (though its being used in related projects), some insulation, etc. I also put a lot of money into the HVAC that I personally think was a waste. It didn't work as it was expected to, and while I knew I was engineering with great compromises, I now thing the compromises were so great that cheap options would have given me the same results. In fact, I now think that having heating/cooling was not needed in my own setup, and that active dead vents would have been better (Admittedly code wouldn't have allowed me to do this).
     
  20. 1_sufferin_mind

    1_sufferin_mind Active Member
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    I am impressed with your thorough itemization! While I may not be able to afford a theater theme or even an upscale aesthetic this first time around, I should be able to swing the soundproofing basics using most of what you've outlined and listed so far. My son is a carpenter, which helps save on labor. But I may still have to abandon adding the room-within-a-room for better isolation. Do you see anything besides a financial benefit in trying to control sound transmission ONLY through the floor and interior walls? If I install a floating floor as described in Post #16, would transmitted sound be attenuated downstairs, or would it remain roughly the same because of leakage through the walls?
     

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