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post #1 of 29 Old 06-21-2016, 10:55 AM - Thread Starter
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Advice needed on dedicated theater build

I'm in the early planning process for a dedicated theater build in my basement. The space is roughly 28 feet long and 14 feet wide. Once the walls are up it would likely be more like 12 by 25 feet or so. I consider this a good sized theater. I wish the space was wider, but its just a limitation of the house.


First, any thoughts on which is better, facing the long way or wide way of the room? My knee jerk reaction was to have it be a 12-13' wide theater space but with lots of depth because I felt it was more critical to have proper distance from the screen and main speakers over the distance to the surrounds. It also allows me to have a screen that nearly fills the front wall which I think will be more immersive. I feel like 12' is just not enough depth. Do you agree? If not, why not?


Ok so because I'm starting with a blank slate, the room length is not set in stone, but there is an I-beam that I want to take advantage of for the rear wall. I've read that acoustically this is better, and since this will be an isolated theater, I do want to take advantage of rigid structures like that for the walls. Beyond the typical room modeling softwares that is available, anything I should think about with regard to room dimensions and seating position to ensure the best sound. I know I want to place the listening position in the location of the flattest and best response (i.e. not a modal null) while also dimensioning the room for the least detrimental modal problems.


Construction will utilize green glue or similar on hat channel. The original plan was to save money and only do this for the ceiling and rear wall, since the other three walls are poured concrete. however, I believe that I would be creating a sound penetration that could escape the theater if those walls also aren't isolated as they still open to the floor above. Is this correct? The only other option is to extend the ceiling. I've also read and been told multiple times now that a CLD floated wall like this offers significant LF damping, so they act as bass absorbers. That seems a good reason to do more rather than less, get as much LF damping as I can. Maybe this next question is better suited to a dedicated acoustic thread, but...should I consider more LF absorption? From what I've read in journals or been told by actual scientists in this field, velocity absorbers are not as effective at low frequencies. Two people I trust quite a bit had actually told me that given my room plans, no additional bass traps are needed or suggested (Peter D'Antonio and Earl Geddes) yet I do read constantly about people have a very different experience, including Ethan Winer, who seem to prefer having more broadband absorption with good LF absorption properties. I feel a bit like I have one camp telling me avoid wasting room space and resources on these porous absorbers given my room and another group touting a fairly contradictory view. I think the nuanced view on this is that while porous absorbers are not efficient LF absorbers when placed in an area of pressure maximum and velocity minimum, they aren't literally at velocity=0 and so they still are doing something, just not as much as they could be. Increasing their efficiency means limiting their bandwidth in ways that can be undesirable. As for multiple subwoofers, that is a given. I use them now and will continue. In fact the dedicated space will involve redesigning my current subwoofers and will consist of at least 3 distinct LF source locations. Because its a dedicated build, I have some ideas that would involve even more LF source locations using a modified MLS location sequence.


While I know I can add panels later, I want the room to look like everything was built in, I want the room to basically look like a minimalist sparse room with everything hidden away, yet I want no acoustic compromises to do that. That means I need to think this out clearly and plan it now.


Ok next acoustic problem (Again, remember I want no acoustic compromises really, within reason anyway), I am worried about over-damping the room. From what I've heard from reading Floyd Toole, Peter D'Antonio, and Earl Geddes, a decent body of literature now exists that has shown through precise experimentation that a room that is too damped will have poor sound quality (which Dr. Toole defines as not sounding airy or real). I've never had the honor of talking directly to Dr. Toole about his research, but I've talked with some of his associates, Dr. Geddes, and Dr. D'Antonio and all have suggested that theaters are often over-damped and that while it is harder to get right, keeping the room more likely is beneficial.


Ok so heres the rub and where I need some advice, Everything they say is based on research done in a lab where the environment was precisely controlled using equipment and a setup that we would never recreate in our homes. The resources thrown at that research is beyond what we can achieve or would want to replicate. Peter seems to suggest that my theater should basically look like Blackbird Studio (RPG actually suggested their more modern diffusers, but you get the point). Floyd Toole doesn't have specific recommendations for how to achieve this goal, but suggests not absorbing all early reflections and including more reflective and diffusing surfaces (But I'm sure doing this haphazardly would sound terrible). Earl Suggests some things that I understand better, he often is very practical, but which contradict some of his own claims, so it leaves me a bit confused. For example, he suggests no absorption in the room at all beyond the damped walls, not diffusion (because haphazard diffusion would be worse than no diffusion), a carpeted floor and absorptive ceiling. I'd love Ethans direct comment on this, but my guess is he would suggest quite a bit of absorption. My concern is that this is in contrast to Dr. Toole's findings, which were replicated in at least two distinct studies done with real environments and numerous auralization studies. As a statistician and research expert I tend to trust numbers more than experience because our eyes and ears can deceive us so readily.


My thought is that I should have a mix of absorption and diffusion. I think maybe having hard floors could actually be a good thing. What I've read a few times is that studios nearly always have hard reflective floors because it improves are perception of location. This might not translate to a theater space, but if its true that speakers sound worse to us in an anechoic condition, maybe not. I could also always add in an area rug near the speakers. Now before everyone jumps all over this as crazy, I was thinking that would include significant absorption and diffusion on the ceiling itself, where I could easily get away with 4" of porous material, far more than I can do at the first reflection point on the floor. That way I'm absorbing a far broader frequency range. Are there people who tried this and later regretted it? Wished they had put down carpet with a thick pad?


Currently I have a mix of acoustic treatments that I will transplant to my theater space. What I have includes Vicoustic Wavewood panels which are diffsorbers using modified MLS sequence. The sidewall has curved RPG Bad Panels. The Corners have Vicoustic Wavewood bass absorbers with rockwool behind them. I was also thinking I could enhance the Wavewood panels in the dedicated theater by mounting them away from the wall and fill the cavity with 2" of fiberglass or rockwool (or whatever I use). Again though, I want the room to look purpose built and clean, so I was thinking of using a stretch fabric system that I could build around the panels so it all looks flush and clean.


Ok next concern How to mount all of the speakers in the most optimal way. It seems like an acoustically transparent screen is a good idea, and it needs to be as acoustically transparent as possible. I'll worry about what material later, but I've interested in looking more into the new material from AVS, and if not, possibly a spandex screen. I'll get samples and do tests when I get closer to an actual build. More what I'm worried about is the issue of diffraction around the speaker. It seems to me like a common practice of placing a speaker into a chamber has numerous problems. One is that its a chamber, so it can impact the low frequencies if not well damped. Second, any gap around the speaker becomes a point for diffraction. If its recessed, its worse yet. Where does the insanity stop here? Is there a best practice for mounting the mains into a baffle wall that minimizes diffraction? I understand that one solution is having a fully absorptive baffle wall, but isn't it typically only about 1" thick? That limits the absorption to about 500hz on up. Is that fine for this? Which is better recessing it and then having the absorption material extend past the front baffle (which would impact the dispersion horizontally and vertically at 90 degrees, but my speakers are already fairly narrow controlled dispersion). Flush? Proud?


Ok how about surrounds? It seems like flush or very slightly proud on a wall that is surrounded by absorption is good. Paul McGowen actually mounted his speakers away from the wall and used a diffused design (Bi or Dipole I believe) which surprised me. I actually use a Tripole now but planned to switch to multiple direct radiators, possibly even CBT. Any tests on this, thoughts, good reads? I can't seem to find anything definitive, just a lot of mixed opinions.


My plans right now are to obtain blueprints for the house and work with my sister, who is an architect to plan the rooms overall design. To plan the relocation of the HVAC (That a fellow AVS friend has offered to help me move), and to plan the key locations of things like the screen, speakers, primary listening position, secondary listening positions, door into the room, etc. From there it will be easier to plan the rest of the room. As I said though, because of my desire to build everything in and keep the room as clean and uncluttered as possible, I feel like I need to worry about the acoustics now and include them in the plans. Any help is much appreciated.


-Matt
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post #2 of 29 Old 06-21-2016, 03:26 PM
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Connecting theater walls to rigid items like a steel I beam is not a good idea from a sound isolation perspective.
If you isolate the framing on the walls facing the foundation by attaching the top plate with IB3 clips you can skip the clips and channel and gain that width.
I have talked with Dr Toole and he recommends that about 25 % of the interior surfaces be covered with absorption .
If you try to reconcile all of the information available from the "Experts", Designers, Vendors and the well wishers on this forum you will never get your theater built and it will lead to the insanity you reference. Hire a qualified designer/acoustics consultant and follow their design don't try to second guess it.
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post #3 of 29 Old 06-22-2016, 08:38 AM - Thread Starter
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Thanks Jeff,


So what I had heard, and maybe this is wrong, is that the I beam is a good solid structure to mount the outer "solid" wall to, and that the inner floating wall must be decoupled from this. That using the Ibeam can make the outer wall more solid. Is that not true? The person who told me this also said that the wall had to be "hung" from the I-beam. Maybe what he meant was decoupled when he said hung. This back wall would have 4 layers of drywall in total. The outer wall would be a normal stud wall, the inner wall would then have the hat channel and 2 layer drywall with CLD. Again, maybe this is wrong, that is just what I thought would provide the greatest degree of isolation. It seems like the rear wall and ceiling are the two areas that need to be built with the greatest degree of isolation to prevent sound leaking as they are the most open.


To prevent sound from escaping the theater via other avenues, would it make sense maybe to do the ceiling before the stud walls go up so that the ceiling actually extends past the walls and is totally sealed to the upstairs. That way when the stud walls do go up and are sealed to the already installed ceiling, there are less (if any) alternative paths? I know that a room within a room is an option to totally fix this, but I would lose too much space I think if I did that. I have a nice 8 foot basement, but that isn't really that much. Add in a ceiling, floor, etc. and suddenly there is nothing left. Float the floor and ceiling and now you are talking about everyone ducking to walk into my hobbit theater.


The outer walls can't mount against the concrete unfortunately. There are drains and water mains that run along two of the outer walls. The wall with the escape windows could have it mounted against the wall. As I understand it, the CLD only offers significant LF damping if there is an airspace and some fiberglass fill. Without the fiberglass the amount of LF damping is reduced drastically, and without an airspace it is non-existent. There is also a staircase in the way on the left wall near the back so the room won't be symmetric totally. My plan is to align the space such that the listeners are in a symmetric space, but I need to figure out where the stairs get in the way and decide from there how I will align it. I'm hoping to take advantage of the higher width by keeping everything pushed forward and having the stairs be more of a bar area, but we will see, that might push things too far forward.


I don't understand how some are so lucky to have nothing in the basement that gets in the way. I have electrical lines, water pipes, drain pipes, HVAC, you name it. NOTHING can be mounted directly to the walls or joists in this basement and it is not even feasible to reroute most of this, just have to build around it.
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post #4 of 29 Old 06-22-2016, 10:12 AM
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Matt, I got your email. Yes, that's an awful of of questions.

Pretty much everything you asked in your first post is answered clearly and completely in the various articles on my two web sites:

Ethan's Articles Page
RealTraps Articles

This short article especially answers your initial questions:

How To Set Up A Room

You mentioned owning acoustic treatment products from various companies. As their customer they owe you one-on-one support and advice. Not that the advice in this forum is lacking.

Here's one more for good luck:

Acoustic Basics

--Ethan
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post #5 of 29 Old 06-22-2016, 10:54 AM - Thread Starter
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Ethan I know its a lot of questions. My only issue is that your articles often are from the perspective of general or mixing room advice, so does the same always apply to a theater space?




Maybe my biggest question for you and others now is the reflective floor with absorbing ceiling. I know your personal preference seems to be with absorption over diffusion at first reflection points and generally with absorption over diffusion. My take is you prefer a highly damped room. Others disagree with that view, but like Jeff said, if I tried to reconcile every expert I'd never finish this. For me at least, absorption is easy, diffusion is not.


I know your stance on other manufacturers products, but because I have a mixed set and because of the opposing views of these and other companies, I'm not really getting anywhere. They also won't offer free advice since they sell services to do this. My personal relationship with some of these folks not withstanding, they would prefer I higher them as consultants. The advice I get is typically restricted to just setup of their devices. What devices I need, where they should be placed, using them in ways they didn't test for, none of that is something they are willing to answer. For example, Vitacoustic won't comment on the advantages of mounting their panels on top of fiberglass. but it's likely that is a good thing for increasing the absorption lower since A) Foam doesn't typically absorb as low and B) any added depth is an advantage.


So back to the floor and ceiling. Is this a nutty idea? There is no way a floor can ever be made to absorb as well as a 2" or 4" panel can, right? If I can put that on a ceiling and not on a floor, isn't that better? If Floyd Toole's findings are right and the reflection off the floor and the sidewalls is actually an important part of how we perceive the sound image, then keeping it is important? If absorbing on the ceiling raises the perceived height of the ceiling, that also seems good. I know I can do both, carpet on the floor and absorption on the ceiling, but like I said, I am worried about making the room too damped.
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post #6 of 29 Old 06-22-2016, 11:14 AM
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Originally Posted by Mpoes12 View Post
To prevent sound from escaping the theater via other avenues, would it make sense maybe to do the ceiling before the stud walls go up so that the ceiling actually extends past the walls and is totally sealed to the upstairs. That way when the stud walls do go up and are sealed to the already installed ceiling, there are less (if any) alternative path
This came up a few days ago, from a sound isolation perspective there is some merit. However, in the unlikely event that the ceiling needs to be replaced due to water damage from above you will regret that decision.
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post #7 of 29 Old 06-22-2016, 11:24 AM
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So what I had heard, and maybe this is wrong, is that the I beam is a good solid structure to mount the outer "solid" wall to, and that the inner floating wall must be decoupled from this.
You didn't mention using double wall construction earlier. I really don't care if you attach the outer wall to I beam but I can't see any benefit to attaching either wall to structural elements, that just increases the vibration pathways to the rest of the house. I'm not aware of any science that says attaching one edge of a wall to something like a steel I beam improves it's STC rating.
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post #8 of 29 Old 06-22-2016, 11:46 AM - Thread Starter
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You didn't mention using double wall construction earlier. I really don't care if you attach the outer wall to I beam but I can't see any benefit to attaching either wall to structural elements, that just increases the vibration pathways to the rest of the house. I'm not aware of any science that says attaching one edge of a wall to something like a steel I beam improves it's STC rating.

That's what I meant when I referenced the CLD floated wall and green glue, sorry I wasn't more clear. Yes it will have many layers of drywall. It was my understanding that to get the right level of STC that I'm looking for, and to have the advantage of LF damping I'm looking for, there needs to be a solid wall behind the floating wall, and that one layer of drywall on the back side of the stud wall is not really sufficient. I just assumed this was standard practice.


Basically I want to be able to listen at reference levels without waking anyone up or even bothering people in the rest of the house. I like to listen very loud and my wife does not nor does she support this hobby. best I can say is she tolerates it, but she isn't into movies, she could care less how her music sounds, and everything I do or want is complete insanity. I convinced her that soundproofing the theater is a good use of money, she now agrees, but I think doing so requires that I don't try to save $1000 here or there on a subpar job. For the sake of argument, lets pretend like the drywall is $10 a sheet, this 13' by 8' wall would take either 8 sheets done cheaply or 16-32 sheets done the right way, in the grand scheme, will I really care if that one wall cost $80 vs $450 to construct given that we are talking about more than triple the STC rating of the wall. Of course my door situation could totally screw this up.


I'll have more posts about this later but because of the above requirement, I need to be sure that the HVAC is isolated as well and again, want to do it as cheaply as possible.
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post #9 of 29 Old 06-22-2016, 11:50 AM - Thread Starter
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This came up a few days ago, from a sound isolation perspective there is some merit. However, in the unlikely event that the ceiling needs to be replaced due to water damage from above you will regret that decision.

fair point. This area of the basement has no bathrooms or kitchen above it or even near it. The living and dining room are over it. The water main does run up the wall near it however, so I probably should avoid that.


Gosh! I didn't even think this through yet. This one wall has the primary drain access and water main. I need access to those, how do I keep the STC rating high for this wall? It's a cement wall, so its not as critical as some, the problem is the ceiling. making sure the sound doesn't radiate through the wall and up into the ceiling in the space behind the wall (where these pipes are located) while also giving access to them. Would a CLD panel with gaskets be my best bet. Something that can be unscrewed if need be? This will be behind the screen, speakers, etc. so it doesn't need to look finished.
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post #10 of 29 Old 06-22-2016, 12:08 PM
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CLD is constrained layer dampening and can be done on a single stud wall, staggered stud wall or double stud wall. I would not attach a single or staggered stud wall to the I beam as it will transfer vibration, If you want to attach the outer frame wall in a double wall construction to it I have less objection. CLD drywall assemblies can be mounted directly on studs or isolated with a clip and channel system. The latter is preferred.
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post #11 of 29 Old 06-22-2016, 12:17 PM - Thread Starter
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I'll be doing Clip and Channel. It's needed to gain the LF damping. While the dissertation project that supports the LF damping of floating CLD walls never tested the other option, still have to follow what the science found effective. And the bonus is the higher STC rating.


I'm trying to hide a post holding up the I-beam in the wall. I hadn't realized that creating a solid wall and then floating CLD drywall onto that solid wall was a problem, as I said, what I was told was that it was a benefit. Since the cost of having two walls is minor and the STC only goes up, I can do that.


I debated having a hallway into the theater so the hallway could be decorated in some cool way, maybe this is a solution as well. It also would allow me to offset two doors and fix the door soundproofing problem mentioned earlier. Each door would still be a solid core door with gasketing, but then I don't need two in a row which I think will look strange and annoy guests.
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post #12 of 29 Old 06-22-2016, 05:03 PM
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Big is right. You are asking all the right questions, but you are at a point where there is more conflict than resolution. While it appears you are trying to understand all the ins and outs via a scientific perspective, keep in mind there is a huge "art" part to this subject. If you need help understanding how to sort through all of it, let me know.
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Big is right. You are asking all the right questions, but you are at a point where there is more conflict than resolution. While it appears you are trying to understand all the ins and outs via a scientific perspective, keep in mind there is a huge "art" part to this subject. If you need help understanding how to sort through all of it, let me know.


Thanks for the offer and I will surely keep that in mind.


I plan to work with my sister on some sketchup models based on the blueprints. We will figure out what needs to go where (generally) and make plans for where to move the HVAC. I'll work with my friend locally on doing that if he is still willing, but if its too crazy, we may just build the ceiling around it. I'll do some different room sizes modeling to figure out the best placement of the seats and where to place my hard walls. As I said, three are fixed, but one isn't, so if shortening the room a little helps, why not. I have some very rough ideas in my head of where I want things but not how to do it or what it will look like.
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Why would you shorten the room? Also, make sure your sister understands 20 dB noise floor, flow rates necessary for a theater, turbulence, sound isolation for ducting that works both ways, and placement of vents and returns for a theater.
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post #15 of 29 Old 06-24-2016, 08:21 AM
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your articles often are from the perspective of general or mixing room advice, so does the same always apply to a theater space?
Yes! I check mixes (and also mix) in my living room home theater all the time. Also, I made a separate "hi-fi and home theater" version of my Basics article a few months ago:

Acoustic Basics

Quote:
I know your stance on other manufacturers products, but because I have a mixed set and because of the opposing views of these and other companies, I'm not really getting anywhere. They also won't offer free advice since they sell services to do this. My personal relationship with some of these folks not withstanding, they would prefer I higher them as consultants. The advice I get is typically restricted to just setup of their devices.
Oh geez, that's so lame. Had you just bought even one or two pieces from RealTraps I'd gladly spend an hour on the phone with you answering all your questions about all of your products for free.

Quote:
So back to the floor and ceiling. Is this a nutty idea? There is no way a floor can ever be made to absorb as well as a 2" or 4" panel can, right? If I can put that on a ceiling and not on a floor, isn't that better?
Well, you could put thick panels on the floor, but it would look silly and it isn't really needed. So put the absorption on the ceiling, and have plush carpet or at least a thick throw rug on the floor at the reflection points.

Quote:
If Floyd Toole's findings are right and the reflection off the floor and the sidewalls is actually an important part of how we perceive the sound image, then keeping it is important? If absorbing on the ceiling raises the perceived height of the ceiling, that also seems good. I know I can do both, carpet on the floor and absorption on the ceiling, but like I said, I am worried about making the room too damped.
LOL, you need to pick one expert and follow their advice.

Seriously, the notion that a room can be too dead sounding is mostly misguided. I have 44 acoustic panels in my living room and it's not at all too dead sounding. Have you seen my article about this? It's very detailed:

Early Reflections

The video version is equally enlightening:

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Why would you shorten the room? Also, make sure your sister understands 20 dB noise floor, flow rates necessary for a theater, turbulence, sound isolation for ducting that works both ways, and placement of vents and returns for a theater.

Yeah she has been pretty clear to me that she doesn't really know this stuff well. She went to Syracuse U. and only studied acoustics a little, in her current job, they mostly do engineering work and none of it is with acoustics as I understand it. I'll have to help her best I can from what knowledge I can pick up from books, the web, forums, etc.


I did have a supposed expert come take a look at the HVAC and the general plan and his suggestions were just tooooo expensive. I'm trying to do this on a pretty tight budget. I want to say his bid included $5000 in custom plenum and such.


I should maybe open a new post on this, but I do need to plan how to handle the HVAC. From what I gather, it would be cheaper to install a second HVAC just for the basement than have someone reroute the current HVAC with custom made parts and then add in significant sound isolation. From what I've read and been told simply lining the ducts with acoustic material will do very little to stop sound transmission from going from the theater to other rooms. As it stands there is fairly little sound that travels through the HVAC between spaces, but its certainly not nothing.


One suggestion from Earl Geddes is simply to create a "U" shaped bend in both the supply and return lines and then line them with acoustic material. He suggested that this alone is enough add significant sound reduction. He also suggested an S is better yet but that you want to make sure you don't create flow problems.


Do those little HVAC mufflers do anything? I can't imagine how they would help much at all.
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post #17 of 29 Old 06-24-2016, 08:44 AM - Thread Starter
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Well, you could put thick panels on the floor, but it would look silly and it isn't really needed. So put the absorption on the ceiling, and have plush carpet or at least a thick throw rug on the floor at the reflection points.

LOL, you need to pick one expert and follow their advice.

Seriously, the notion that a room can be too dead sounding is mostly misguided. I have 44 acoustic panels in my living room and it's not at all too dead sounding. Have you seen my article about this? It's very detailed:

Well Ethan, it would be nice if all the experts just agreed!


As to your other comment, I understand your feeling. I should maybe do some listening tests myself, its not hard to test this. You can place plywood on the floor, add and remove wall panels, etc. I actually am in the process of building some panels right now to test some ideas out. I have a TON of scrap 1x4 and plywood so I'm going to build some sound absorbers and see what I think.


I actually did some of the statistical analysis for a slightly less rigorous room acoustics study which used headphones and aurilization. The test was ABX in nature and the music was a digital recording that then had the room acoustics added back in using the aurilization technique. The statistics I used for this group were pretty sophisticated so I'd like to think the findings aren't totally misguided. At the same time, they are just statistics, meaning this was the preference on average, and the variance of the sample was HUGE. While we had a statistically significant finding and it was consistent with Toole's past research, it was a tiny effect size. The three samples were live room, dead room, and no room. People frequently couldn't tell the difference between dead and no room and there was no significant difference between those samples overall. A subset of what we coined goldenears could reliably hear the difference, two has 100% accuracy. We also did a test on image specificity and the live room was "preferred" but actually the specificity was worse, which if I recall, is in contrast to what Toole had found.


I didn't actually participate in this study at all and never heard the samples, I only received a data file to analyze so I can't speak to anything else. I had nothing to do with the study itself. Just making the point that to call it misguided seems to imply the science behind it isn't sound. Nothing I've seen says that lively rooms are better and I believe only Harman and Toole have actually studied specific room differences directly in highly rigorous ABX scenarios. I know Toole suggested their study says they are better, but I think a fair interpretation is that there was a preference for them. Better here is highly subjective. I also think that the studies I've seen done with lively rooms had atypical rooms. You are not the first to suggest a deader room is better when on the small size, and my understanding of the size of the labs used for the past studies is that they are not only built to a totally different standard from a home, but also somewhat larger than even a modest sized theater.



Thanks again though, this is all helpful in narrowing in on a plan.
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post #18 of 29 Old 06-24-2016, 09:27 AM
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From what I've read and been told simply lining the ducts with acoustic material will do very little to stop sound transmission from going from the theater to other rooms.
will it stop 100% no.
will it greatly reduce YES

obviously disconnecting the theater from the rest of the house with a separate system is the best solution, If you can't afford that strategy you need to do everything you can to mitigate the situation, Connecting the theater with sound attenuating duct work is one item you should not forgo, you are talking to the wrong people. You can also use pressurized plenums lined with acoustically absorbent material inside soffits built inside your theater shell to cut the sound entering and leaving the theater space, properly designed the plenums will slow down the air flow to eliminate any air movement sound coming from the duct work. Design the system so that the air speed at the face of any supply and retuen vent is less than 250 ft per minute. You can actually use the soffit carcass as part of the plenum. Avoid metal ductwork. Use insulated flex duct.

Your goal should be a room that achieves a acoustic noise criterial standard of NC20. As a simple test if you can hear the air coming into the room through the supplies it will not meet the standard If sitting in your seat and with no other source of theater sound and you can hear the AC cycle on and off it will not meet the standard. . You often have to hold a piece of paper up to the vent to make sure air is coming in the room because it is so quiet.

more on that subject: http://www.engineeringtoolbox.com/nc...ion-d_725.html

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post #19 of 29 Old 06-24-2016, 10:25 AM
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As Big mentioned, you're talking with the wrong people. Well known acousticians are not designers, nor do they care to be. You need to talk with a good, whole room, designer. You are trying to take tidbits from tons of people, and trying to formulate a complete thought. Won't happen. You'll just confuse yourself more. I believe that's what Big was trying to elude to. There are several from which to choose. Names that come to mind are Anthony Grimani, Keith Yates, Dennis Erskine, Nyal Mellor, Shawn Byrne (SierraMikeBravo), etc. just to name a few. They are well versed in construction and acoustic integration. Make sure they understand the ins and outs of isolation and how it pertains to HVAC requirements. Etc. There is s thread out there with a list of questions to ask a designer. That's my ten cents.
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post #20 of 29 Old 06-24-2016, 11:18 AM - Thread Starter
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The guy that told me not to rely on just duct liner alone was actually an architect who specializes in isolated meeting spaces in high rise buildings. Earl Geddes actually did suggest duct liner, he just said I need to add intentional hard bends to improve the sound reduction and that this was common practice. This other guy was a little more hard line, saying they custom design baffled ducts with many hard bends and perforated metal lined with foam or fiberglass. He had felt that this is what I need to achieve my goals and that I might be better off with a second HVAC system instead.


Are you both suggesting that Earl's idea of the sharp bends lined with duct liner is not needed, that simply using duct liner alone with soft insulated lines hidden behind the acoustically isolated walls or soffits is adequate? I mean, if that is true, I think it would save me a ton of time and money.


I need to reroute the return line anyway, it currently runs along the left portion of the ceiling, maybe 25% of the way toward the center. To regain that ceiling space we were going to rerun it closer to the wall and put that into a soffit. It would create two very sharp 90 degree bends to wrap around the staircase and I figured that might actually work for the return line as the hard bends. I'm going to have these hard bends no matter what, so is this good?
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post #21 of 29 Old 06-24-2016, 11:49 AM
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Bends are good from a sound management perspective, not from a AC efficiency perspective so there is a slight price to pay. I like serpentine pathways. You are asking us to comment on a design that only exists in your mind. I would like to see the entire route, where it enters/exits the theater shell and how it is channeled inside the theater to the final vent faces.
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post #22 of 29 Old 06-24-2016, 11:52 AM - Thread Starter
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Yeah sorry, you make a fair point. At this point it would be premature to show you anything. I could take a picture of the nearly empty space and the current position of the HVAC return line, but that doesn't help. Once I get a copy of the blueprints and can start making sketchups, I can share pictures and plans. We just aren't there yet.
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post #23 of 29 Old 06-24-2016, 12:40 PM
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Then you are chasing your tail. You seem to be asking a lot of hypothetical questions. You need to ask the right questions for your particular circumstances, which you won't know until the time comes.
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post #24 of 29 Old 06-24-2016, 01:06 PM - Thread Starter
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Well maybe for the specifics of the hvac and other details, but for the overall design, seems like the best thing to do is start planning early.


I know I want a sound isolated theater that will transfer a minimum of its sound to the upstairs or outside the theater in general. That means big isolated high mass walls regardless of what it looks like. It means isolated HVAC. Etc. Etc. I want the theater to have a clean very modern minimalist look. My concern is from past efforts I will end up with a cluttered mess if I don't think through all the details now. If I don't want the acoustics to look slapped on, then I can't slap them on after I build the room. Since I have almost no defined space either, I want to build the room to dimensions that maximize the acoustics of the room and give myself places to hide all the speakers and equipment in acoustically benign ways. That's really what I'm trying to work out now.


I'm a little behind on the designs right now because my builder and the city are arguing over who should give me blueprints. I don't even care who gives them to me, I'll happily pay a small fee for them, but I want them. When the house was built I asked for them and was told that is not possible, that I had to pay the city. Now the city says they don't supply them and to ask the builder. Great!
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Matt what ever hvac plan you come up with or I can come up with a plan for you. I'm game for helping you out as I said before. The duct that runs down your room really needs to move to the side along with the return. All the duct work can be hidden in a soffit.
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post #26 of 29 Old 06-25-2016, 12:40 PM - Thread Starter
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Hey mike let's maybe start planning this so we can get a materials list and some sketches of what we will do. I have three or four ideas but you know a lot more about hvac install than I do, having actually done that for a living before. Maybe we can take pics and drawings and post them for advice. Sounds like we need to add duct liner to these runs and isolate them. I can't fully take the advice here and avoid metal because the lines we are moving are the trunk lines (I don't know if that is the right name) for the living room and dining room.

I just don't want to kill my overall budget on just moving hvac. I'd rather leave it where it is and build around it than blow the budget on moving it. Right now my wife and I are not totally on the same page on the budget for this, so I may need to delay some of the final construction and focus on moving hvac, overall planning, and framing for the first year, and then slowly eat away at the rest over the following year.


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Hey mike let's maybe start planning this so we can get a materials list and some sketches of what we will do. I have three or four ideas but you know a lot more about hvac install than I do, having actually done that for a living before. Maybe we can take pics and drawings and post them for advice. Sounds like we need to add duct liner to these runs and isolate them. I can't fully take the advice here and avoid metal because the lines we are moving are the trunk lines (I don't know if that is the right name) for the living room and dining room.

I just don't want to kill my overall budget on just moving hvac. I'd rather leave it where it is and build around it than blow the budget on moving it. Right now my wife and I are not totally on the same page on the budget for this, so I may need to delay some of the final construction and focus on moving hvac, overall planning, and framing for the first year, and then slowly eat away at the rest over the following year.


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Suggest you start by setting reasonable targets for the room's ventilation rate (AC/H, air changes per hour) and noise floor with the HVAC system operating normally, and work backwards from there. If you have high standards in those metrics you will benefit from engaging a mechanical PE with at least a few years' experience modeling HVAC for recording studios, radio stations, Foley stages, auditoria, etc. At the end you will want a mechanical T&B guy to drop by to test & adjust the flow rates, % outside air, etc., and a noise & vibration guy with a mic with self-noise floor below 15dB(A) to confirm that you got what you paid for. You can take it further than this, of course, but unless you've nailed the basic ventilation rate and noise floor, you're spending money to spin your wheels.
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post #28 of 29 Old 07-20-2016, 06:19 AM - Thread Starter
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Suggest you start by setting reasonable targets for the room's ventilation rate (AC/H, air changes per hour) and noise floor with the HVAC system operating normally, and work backwards from there. If you have high standards in those metrics you will benefit from engaging a mechanical PE with at least a few years' experience modeling HVAC for recording studios, radio stations, Foley stages, auditoria, etc. At the end you will want a mechanical T&B guy to drop by to test & adjust the flow rates, % outside air, etc., and a noise & vibration guy with a mic with self-noise floor below 15dB(A) to confirm that you got what you paid for. You can take it further than this, of course, but unless you've nailed the basic ventilation rate and noise floor, you're spending money to spin your wheels.
Thanks Keith I appreciate your thoughts on this. I don't know how much of this I will be able to do, given my budget. My sister has put me in touch with a colleague of hers who does modeling of HVAC for quiet office spaces in NYC buildings, like lawyers offices and such. He has offered to run some models once I get him dimensions and specs, then make recommendations or possibly even test out some of my ideas to see how they would model. I planned on doing the measurements of the noise floor myself, but the self-noise floor is an issue. It was brought up on a post where I attempted to make a measurement at night in my current temporary theater space and while the curve roughly conformed to NC20, further investigation into my mic setup and the room suggests I was lucky to have even achieved that result, if it was even accurate. I certainly don't have a noise foor that is as low as 15db(a). My mic was a DIY measurement mic based on the well regarded Panasonic element, but one problem with that element is that its self noise is actually quite high. I have a modified version with a hand selected element, meaning I bought a ton of them and tested all of them to find the best ones, then modified it to be slightly quieter, but from what I've read online, even what I did was lucky to put my noise floor at 20-30 db(a), meaning my room measurement earlier was probably a mic self-noise measurement as much as anything.


I initially had some big dreams, but as I work out everything, including cost, I'm finding I need to make compromises in some of the most costly areas and they tend to also be the areas that impact things like how quiet the room will be with regard to the HVAC or isolated from the rest of the house.
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post #29 of 29 Old 07-25-2016, 12:23 PM
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What is you goal for noise floor ?

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