My New Theater

[Matthew J Poes]

It's been a while since I've updated this thread with our progress. That's mostly because there hasn't been much progress

I am currently pulling speaker wire in the theater. I decided to also run conduit to all speaker locations, and for subwoofer cables and of course video cable to the projector location. Hopefully I can get the conduit installed this weekend.

I investigated the possibility of doing a minisplit HVAC system for the theater. I found some rather quiet ones (around 20 dBA). Unfortunately, the installed price of these units tops $3000. Considering that we're already over budget on this add-on, we are not too keen on spending that much more. It turns out I don't have enough room for a dead vent, without stealing non-negotiable space from the adjacent room. Long story short, the theater will share HVAC with the rest of the house. I am now looking for inline silencers for the theater supply and return trunks to minimize airborne sound transfer through the ductwork.

My primary concerns with tying the theater HVAC into the rest of the house are: 1. Sound transfer via the ductwork (airborne and breakout noise), which I think I can minimize with careful planning; 2. The potential for the theater to need to be cooled when the rest of the house needs to be heated. Since the theater will be insulated on all sides, and there will be equipment in the room and sometimes several people, it could get quite warm in there while the rest of the house is too cool. I can close the vents in the theater, but that may not be enough and will also introduce air turbulence noise when the HVAC system is running. Perhaps I will have them install a damper ahead of the theater trunk that can be separately controlled.

I suppose if it turns out to be a big problem, I could have a minisplit installed in the future when the bank account recovers.

Anyway, there's the latest for ya.

Having gone down a similar road I can give you all the information on what I did, but I'll warn you up front that silencing ducting is expensive. What I found out was that you need to look for deals and even into custom fabrication as a means to keep costs down. This will all be a balancing act, as perfect is just too expensive to be realistic.

Tidbits on Soundproof Ductwork:

1. Steels ductwork provides similar sound isolation to 1/2" drywall, but resonates significantly and at the resonance frequency allows a great deal of sound to penetrate.
2. Flex duct does not provide any significant sound isolation, nearly all sound that enters flex duct escapes, known as break out noise. Acoustic Flex duct's only advantages to steel ductwork is that sound does not travel down/through the length of the duct and provides physical isolation between the theater and main trunk. Remember that the main reasons that sound doesn't travel down the duct is not just that it absorbs, its also because most of the sound simply escapes. That is important because if you forget that, its easy to install it in a way where it defeats your soundproofing.
3. https://www.acrytech.com/product/acoust-x-sound-damping-coating-5-gallons/ this product provides good damping at a good price for steel ductwork. I used it inside and out on the ductwork near and inside my theater.
4. http://www.jm.com/en/building-materials/hvac-insulation/duct-liner/spiracoustic-plus/ this is the product I used to line my ducts. While duct silencers are good, most of them operate on a principle of absorption over distance and a velocity change via an expansion chamber. What this means is that they aren't special and can be recreated easily. You can equal a 24" long Duct for 6" ducting by simply buying a piece of 24" long duct material that is 9" to 10" in diameter and lining it with 1.5" insulation. Then using reducers on each end. This isn't cheaper if all you do is one 24" duct. The real issue is that the decibel loss is very small, so you need more than 24". Custom lets you make much larger ducts. For example, I would go with 8" instead of 6" and I would increase the size to something like 14" duct for the muffler lined with 2" material, and make it much longer, like 6 feet long if possible. An ideal scenario would have a total of ten feet of absorption or more for each supply and each return. This stuff is expensive so look around and ask for discounts. Don't go to big box stores, they won't have and if they do, the price is unlikely to be good. I got a good deal by buying a damaged roll.
5. Spiral duct is better than snap together round duct, and round duct is much better than square duct. Spiral duct is normally a higher gauge of steel which provides more absorption and its stiffer so it contains low frequencies better. This has been researched and shown to be true, so its a practice worth following. Unforutnately that means you need to use commercial duct in a non-commercial scenario, so price goes up. Again, ask for deals and scraps. I was able to mix commercial and non-commercial products in key ways to save money. Everything into the theater is commercial, everything outside of the theater (after a few feet) is domestic. I also used a acoustic lined specialty product for the long runs in addition to my mufflers, which I don't suggest. It's the same thing as I created and was pretty expensive.
6. Fancier and more effective mufflers exist, it may be worth pricing them out, but...I found they were as expensive as a split system. A muffler could be $1500 or more. They are almost always custom. It is possible someone will have created one for a customer that the customer didn't use, so you might find a deal.
7. Expansion chambers are good to reduce air noise, but should not be too close to the return and supply exits. I don't know what best practice is, might want to consult a professional. Just know that most HVAC companies do not really understand sound and acoustics, so I got mixed information. I contacted a company that specializes in HVAC for large buildings and studios.
8. Expansion chambers with offset entry and exit are better, in general reducing line of sight type scenarios are good, you want the air to have to change direction, but it also needs a surface to absorb on as much as possible.
9. 90 degree bends or any sharp change in direction is good for sound in some ways and bad for sound in others. The indirect path helps more sound to be absorbed by encouraging more reflections and thus more sound hitting the absorption material. The bad is that it causes air turbulence and increase low frequency noise. Turning vanes fix this and acoustic turning vanes are ideal. The problem is they are expensive. If you are more adventurous than I, you can buy prefabricated turning vanes and install them in a custom made expansion box on your own. You might also just ask a local fabricator what the cost is, it might not be bad. The quotes I got were very high.
10. Metal ductwork will transmit sound directly through the metal itself. It vibrates and reradiates the sound. The solution is two fold. One is the damping of the metal (which I did). The other is the inclusion of one or more flexible connections. I didn't do this because I worried it would let sound out. It turns out the flexible vibration break is too important. I should have done it.
11. Lower air velocity makes less noise. Larger ductwork reduces air velocity. Changes in the duct area to a drastically larger one also lowers velocity (so if you then reduce it again, the velocity doesn't increase as much as the velocity before the expansion).

Other things to think about are what you can do inside the room. For example, acoustic flex duct is very cheap compared to the products I listed above. While it doesn't work as well, if you can have a soffit, you could create a sound isolated soffit (where the entire soffit is isolated from the rest of the house) and burry the flex duct inside of that. You could even put lots of bends inside it and then cover it with blown in insulation. This would be like a dead vent inside the room basically.

I'm looking at building additional soffits near my ducts that will cover the ducts and be lined with Ductboard. This will create and indirect entry to the duct and provide a lot of sound absorbing surface, as well as a large in room expansion box. While I said earlier expansion boxes shouldn't be close to the exit, what I found is that there are two ways these are done. One is an expansion box in the traditional sense. Because of the offset entry and exit, they can cause noisy turbulence. The other is more of a giant flare, and this kind of expansion box does the opposite, it doesn't create turbulence and actually reduce airflow sound. Here is an example:


When I get a chance, I can share drawings of my idea, which is similar to this, but creates a more indirect path for the air to travel.

Oh one last thing, pick your vent covers carefully. Vent covers can generate noise. A number of people complain about this. My solution was to reduce air velocity as much as possible. None the less, I do find the vents add a little noise. Linear vents are more aerodynamic and work best, but they are really expensive. If you find a cheap solution let me know. I don't have one myself.

 

[Tony V.]

Lots of good stuff in this thread so I will be watching it closely

 

[Todd Anderson]

Who knew there was so much to do about duct work!?? Wow!

 

[Matthew J Poes]

Hah, don't get me started on doors!

 

[bkeeler10]

Well, unfortunately the realities of modifying existing construction have come home to roost. After speaking with the HVAC guy about his plans, I realize that there's not much I'm going to be able to do to address the ductwork issues. We're already going to have ceilings come down 8" in rooms adjacent to the theater to get the required airflow. Running lining in the ducts would require another 2" (so that interior duct cross-sectional area can be maintained). There will be a new main from the furnace to feed the theater, but the same main will feed the entire addition. We don't have room for silencers just as we don't have room for larger-diameter ducts. About the only thing I'm going to be able to do is get a larger cross-sectional area just before the ducts dump into the air exchangers in the theater, to slow down velocity and reduce turbulence noise.

So tempted to bite the bullet and spend the $3k on the minisplit. But decisions like that are exactly the sorts of things that make construction take twice as long and cost twice as much as you expected it to.

 

[bkeeler10]

Lots of good stuff in this thread so I will be watching it closely

Agreed, and Matt has been extremely generous spending his time conveying information from his studying and experience, which I greatly appreciate.

 

[Matthew J Poes]

Well, unfortunately the realities of modifying existing construction have come home to roost. After speaking with the HVAC guy about his plans, I realize that there's not much I'm going to be able to do to address the ductwork issues. We're already going to have ceilings come down 8" in rooms adjacent to the theater to get the required airflow. Running lining in the ducts would require another 2" (so that interior duct cross-sectional area can be maintained). There will be a new main from the furnace to feed the theater, but the same main will feed the entire addition. We don't have room for silencers just as we don't have room for larger-diameter ducts. About the only thing I'm going to be able to do is get a larger cross-sectional area just before the ducts dump into the air exchangers in the theater, to slow down velocity and reduce turbulence noise.

So tempted to bite the bullet and spend the $3k on the minisplit. But decisions like that are exactly the sorts of things that make construction take twice as long and cost twice as much as you expected it to.

https://www.homedepot.com/p/Master-...ister-Box-Side-Outlet-R4-TIRB10X6X6/204164414
Could this be an option? It's like a mini expansion box and would provide some sound insulation. It comes in different formats.

Can you put a duct muffler in your HVAC room? If you can get any acoustically lined duct between your theater and the rest of the house, that should be beneficial.

Can you damp the metal duct at least? That won't add any thickness really and still helps reduce the sound from escaping the duct at the resonant frequency by damping its resonance.

a flex connector might also be good. I haven't done exhaustive studies of this myself, but....My system has a measurable low frequency rumble in the ambient room noise that I believe is HVAC related. A friend of mine installed a few flexible connectors to isolate his HVAC system from the house and his theater, my measurement of his room didn't have as loud of a LF rumble. He has two HVAC systems and his theater is a similar distance to his equipment room in his basement. I think that is a sign of the effectiveness of these flex connectors. If nothing else it just makes sense that this would be true.

I forgot to mention this before, wrapping a duct in a fiberglass insulation jacket isn't helpful and can actually create a low frequency conduit for sound. A lot of folks do that because its easy. It does insulate the duct against heat or cold loss, but it doesn't provide an acoustic advantage and was found in one study to provide an acoustic disadvantage.

I'll also mention that I have a VERY soundproof theater room, the noise floor is much lower than any other room. It isolates to a very high degree and in many ways I went all out. I can still hear people walking above my theater, I can still hear some house noises in my theater, and my wife says that while she can't really hear the music or movie much, she says the entire floor above the theater shakes when I watch a loud movie or listen to music with a loud bass line. She also says its audible, maybe not loud, but loud enough to be bothersome if she is relaxing quietly. It just seems that it is not possible to get perfect sound isolation without going for heroic measures. I believe some of the sounds I hear and that my wife hears is coming through the ducts. We plan to replace the carpet with hardwood floors this year and I plan to install a second layer of subfloor with green glue and put down something like whispermat underlayment to see if that helps. I'll let everyone know if that makes a difference.

I spent a lot more than I expected to because of all these issues. If I had it to do all over, I would have planned a little better and found ways to be more financially efficient in achieving my goals. I'm glad you at least find this all helpful.

 

[bkeeler10]

Thanks Matt. I think that the expansion box might be worth a look, as compared to what they plan to use. I also think a resilient connection from the furnace to the ductwork will likely help keep vibration-induced noise out of the theater, and shouldn't be too expensive money-wise or space-wise. I will look into whether a muffler/silencer on the new feed at the furnace room will fit. It would have to be in the furnace closet - that's the only place that might have room for something that big. It looks like those can be had for around $100.

At this point, given the constraints, I'm going to focus on doing whatever I can to keep the noise floor in the theater as low as possible. The good news is that there are no bedrooms immediately adjacent to the theater. The room above is a great room/kitchen, and the room to the side is a family room. So the rooms that must be quiet will have a buffer zone between them and the theater. Hopefully this will mean they are still okay.

 

[AudiocRaver]

Hey, Brian, good to see your progress. I'm dealing with a lot of the same issues in designing my room, primarily soundproofing.

 

[Talley]

Run ENT for the conduit. Super easy to bend and it will be continous. I'm a master electrician and reading this thread I was like OOOoooo run conduit run conduit...

Glad you decided to do that. Just in case you need to pull another speaker cable or replace etc... Run 1" for the HDMI. 3/4" for the rest.

 

[bkeeler10]

Hey, Brian, good to see your progress. I'm dealing with a lot of the same issues in designing my room, primarily soundproofing.

It's a pain, isn't it? And it's particularly frustrating to have to make compromises, whether because of budget, or other practical concerns. I have to keep telling myself that it's going to be quite a bit better than what I have had previously, regardless of what happens.

 

[bkeeler10]

Run ENT for the conduit. Super easy to bend and it will be continous. I'm a master electrician and reading this thread I was like OOOoooo run conduit run conduit...

Glad you decided to do that. Just in case you need to pull another speaker cable or replace etc... Run 1" for the HDMI. 3/4" for the rest.

Thanks. I had been planning on smurf tube. But I will look into ENT. What are its advantages? Is it less expensive?

Also, I had be planning on 1.25" or 1.5" for HDMI, and 0.5" for speaker and subwoofer cables (unterminated). I think I will still go to 1.25" for HDMI. Do you think I need 0.75" for the others?

 

[Talley]

I ran 3/4" for the speakers. 1" should fit the HDMI but bigger is always better.

Also... Smurf Tube is street slang for ENT. We are talking the same language

 

[bkeeler10]

Perfect, thanks Talley. Does the stated diameter refer to interior or exterior diameter?

Edit: Also, if I'm running it in the space between walls (as opposed to going through studs or joists), what should I use to secure it to the side of a 2x4, and how far apart can those supports be?

 

[bkeeler10]

Wow, it's been almost a month since I've updated the thread on progress. We had problems with a couple of subs (HVAC and plumbing), which caused big delays. But that's all done now. And the electrical is nearly done too. We have our four-way inspection tomorrow, which we will hopefully pass and be able to move on.

In the theater, I have finished wiring for 15 speakers (9.1.6 Atmos system, but of course I'll be starting with 7.1.4). I have also pulled 1.25" ENT to the back of the room (for projector) and to the front of the room (possible future TV). I have 3/4" ENT to four subwoofer locations, and to the LCR and side surround locations. I have some constraints that make it difficult to get ENT to the back of the room for back surrounds and rear overhead, but I intend to get conduit to front and middle overhead locations and possibly to the floor-level "wide" speaker locations too.

Here's a question for anyone, but particularly for Matt if he's willing: I intend to terminate all my speaker cable runs into electrical boxes. I haven't been able to figure a way to do this on the ceiling though. As a reminder, my ceiling will be two layers of 5/8" sheetrock mounted on clips. The joists are so far away from the finished surface of the ceiling that I don't think I can mount an electrical box far enough away from the joist to get close to where the finished ceiling will be. I suppose I could forgo the boxes and just punch a hole in the ceiling, pull the cable through and seal it up, but what would I do if I had conduit going to ceiling locations?

 

[Tony V.]

You should be able to use a box like this that will just clamp to the drywall its self
https://www.lowes.com/pd/CARLON-1-G...ard-Switch-Outlet-Wall-Electrical-Box/1098523

 

[Todd Anderson]

I can't wait to see pics of this bad boy when it's done!

 

[Matthew J Poes]

Wow, it's been almost a month since I've updated the thread on progress. We had problems with a couple of subs (HVAC and plumbing), which caused big delays. But that's all done now. And the electrical is nearly done too. We have our four-way inspection tomorrow, which we will hopefully pass and be able to move on.

In the theater, I have finished wiring for 15 speakers (9.1.6 Atmos system, but of course I'll be starting with 7.1.4). I have also pulled 1.25" ENT to the back of the room (for projector) and to the front of the room (possible future TV). I have 3/4" ENT to four subwoofer locations, and to the LCR and side surround locations. I have some constraints that make it difficult to get ENT to the back of the room for back surrounds and rear overhead, but I intend to get conduit to front and middle overhead locations and possibly to the floor-level "wide" speaker locations too.

Here's a question for anyone, but particularly for Matt if he's willing: I intend to terminate all my speaker cable runs into electrical boxes. I haven't been able to figure a way to do this on the ceiling though. As a reminder, my ceiling will be two layers of 5/8" sheetrock mounted on clips. The joists are so far away from the finished surface of the ceiling that I don't think I can mount an electrical box far enough away from the joist to get close to where the finished ceiling will be. I suppose I could forgo the boxes and just punch a hole in the ceiling, pull the cable through and seal it up, but what would I do if I had conduit going to ceiling locations?

I might look into using the acoustic isolation mounts to move the box out (and further isolate it from the studs) and then use a box extender. In my ceiling I just have a whole that I sealed with caulk. The ENT is connected to PVC and the PVC is secured to the drywall with acoustic caulk. For all of my outlets I used a dual to single gang reducer raised in the middle (and dual gang boxes). I then caulked the box to the wall. It created about a half inch lip that the drywall adhered to. I think you could do the same thing in the ceiling.

They also make extenders for boxes and you could combine an extender if you still needed more distance.

Something to consider, the ENT and conduit between electrical boxes create acoustic pathways. To resolve that I plugged mine with some grey putty, the same kind used to seal electrical connections that are run outside, such as to AC units. One thing I learned, make sure you have run all your wires and don't plan to change anything before you plug the holes. I ended up having to unplug all the holes once I was done because I had to run more wires. In fact, they are still unplugged because I still need to run more wires. I still think plugging the holes is a good idea, I just should have waited.

I would consider doing this at every box, but probably wait until after any inspections. I don't know if it would pass code.

 

[Matthew J Poes]

You should be able to use a box like this that will just clamp to the drywall its self
https://www.lowes.com/pd/CARLON-1-G...ard-Switch-Outlet-Wall-Electrical-Box/1098523

The main problem with these plastic retro boxes is that they aren't acoustically sealed at all and its very difficult to seal them before installing them. You would have to apply the acoustic sealant to the inside , which likely wouldn't pass code (and would be hard to do). I prefer to always use metal boxes (even for low voltage) because it has a higher sound transmission loss, and then wrapping it with putty pads. This is done before the drywall goes up, and then you use extenders to reach the drywall surface.

Otherwise its a good thought and if sound isolation isn't a concern, is a much simpler solution to my approach.

 

[Todd Anderson]

The main problem with these plastic retro boxes is that they aren't acoustically sealed at all and its very difficult to seal them before installing them. You would have to apply the acoustic sealant to the inside , which likely wouldn't pass code (and would be hard to do). I prefer to always use metal boxes (even for low voltage) because it has a higher sound transmission loss, and then wrapping it with putty pads. This is done before the drywall goes up, and then you use extenders to reach the drywall surface.

Otherwise its a good thought and if sound isolation isn't a concern, is a much simpler solution to my approach.

Matt, the build of your room must be INSANE!

 

[Matthew J Poes]

Matt, the build of your room must be INSANE!

The rooms Transmission loss is pretty high. I planned the room from a conceptual standpoint. I wanted at least 50dbs of transmission loss on average across the board. To do that you have to design the entire room to achieve that. Once you exceed 30-40dbs of transmission loss you quickly realize that everything in the room is a potential sound leak. The doors, windows, outlets, etc. even the solid cement foundation is an acoustic sound path! Once you learn that and how to address it, the kinds of details you pay attention to become nuts.

I made a lot of mistakes in my room though and I learned from them. It’s hard for me to tell my exact transmission loss values but best I can tell a good amount of sound at low frequencies leaks out into the living room over my theater. The leak is primarily in one corner and I still am not sure why. I plan to add more sound isolation between floors when I install hardwood floors to resolve this. I should have done the ceiling differently.

 

[bkeeler10]

I've updated post 2 (or is it 3?) with a couple new pictures of the theater's progress. Those were taken maybe a week ago. The wiring is now completely done, the conduit is installed, and the insulation is in (I'll try to take pictures of that, but it is really dark in there now

I spent a couple of hours today rearranging the fiberglass in the ceiling. It had been compressed and stuffed into the corners and around the ductwork -- not good. I was surprised after I was done at how much insulation I removed. I told them to not compress it, but apparently their definition of compressed is different than mine.

I have in hand my IB-1 clips, green glue and putty pads. I started laying out where the clips need to be installed today. I will be working on installing them and the putty pads over the next week. Sheetrock was supposed to be started next week, but it got delayed and it's a good thing too -- it will take longer to get ready than I thought. Just like everything else in this whole add-on project . . .

 

[bkeeler10]

Quick update: Perhaps 1/3 of my ceiling clips are installed. However, I've been told that sheetrock is coming tomorrow. Looks like it's gonna be a late night for me . . .

Quick question for anyone who is following along. I plan on having a projector hush box installed. It won't be fully closed in though - instead it will open into the room behind the theater. It will probably be a little over 2' wide, about 2' deep and maybe 2' or so down from the ceiling. So the opening into the room behind will probably be around 2' x 2'. Two questions regarding that:

1. Will passive cooling be enough to keep the projector cool? I'm hoping that with such a large opening, the projector's fans will move enough air that there won't be a problem. But this is especially concerning since the elevation where I live is about 4600' above seal level. Meaning I will have to turn on the high altitude option and run the fan faster anyway. Perhaps I will need another fan in there somewhere.
2. Does anyone have a recommendation for a glass piece that the projector's light would pass through?

Thanks.

 

[bkeeler10]

Still don't have sheetrock. Clips are mostly up now though, which will be finished before the end of the week.

I've been looking at sound-rated doors, and they are simply out of reach price-wise for now. The best value I could find was the IsoDoor HD at isostore.com. STC 49 (or STC 45 but with better low-frequency performance), and that's still $2500. And I need two (one for the entrance to the theater, and one for the back of the equipment closet). Even buying one is a stretch, but two is simply out of the question.

I wonder if I can obtain similar performance with two standard solid-core communicating door slabs with seals and door bottoms. Selling the communicating doors to the wife will be difficult. But selling $5k worth of doors is even harder. I can't even sell myself on it at this point! It's a shame - that wall is double stud and should perform very well, so it is disappointing to have to compromise on the doors.

This soundproofing stuff is expensive!!

 

[Matthew J Poes]

Still don't have sheetrock. Clips are mostly up now though, which will be finished before the end of the week.

I've been looking at sound-rated doors, and they are simply out of reach price-wise for now. The best value I could find was the IsoDoor HD at isostore.com. STC 49 (or STC 45 but with better low-frequency performance), and that's still $2500. And I need two (one for the entrance to the theater, and one for the back of the equipment closet). Even buying one is a stretch, but two is simply out of the question.

I wonder if I can obtain similar performance with two standard solid-core communicating door slabs with seals and door bottoms. Selling the communicating doors to the wife will be difficult. But selling $5k worth of doors is even harder. I can't even sell myself on it at this point! It's a shame - that wall is double stud and should perform very well, so it is disappointing to have to compromise on the doors.

This soundproofing stuff is expensive!!

It is so expensive.

I wrote an extensive article on this for AVS.

The short answer is yes communicating doors can give similar performance. In fact at low frequencies they will largely give better performance. What you want is two solid core doors that have the highest individual arc ratings. While many people suggest exterior doors, my research found those doors are no better than interior with gaskets.

I found some doors from companies like Mohawk with premium mineral cores that had STc ratings up into the low 40’s or even higher. Two of those with a 6” gap and good gaskets will have an stc rating in the low 40’s or low 50’s. Increase that gap and you are into the mid 50’s. Add an acoustic panel to one of the doors and you can add even more stc points. I think you get the point. Communicating doors are great, far better than a single door at blocking sound.

I forget the exact doors I bought but one had an STC rating in the mid 30’s and the other was like high 30’s or low 40’s. It’s a 1.75” mineral core door. Often these are fire rated doors.

At the time that I wrote the article I was convinced that solid core was essential (because that’s what I had been told). Actually! There isn’t a lot of difference between a solid and hollow core door in sound transmission loss and in fact commercial doors are not really solid core. They are a complex composite and often contain insulation or an air gap. With communicating doors I still think they make sense since they are already a composite.

Some people like to adhere with greenglue a layer of mdf to the door to make it more soundproof. I have data on this. It adds about 3-5 STC points at best, in a number of tests it added only 1-2. Still that’s better than nothing and fairly cheap. With communicating doors I suspect that would be a more effective strategy but it is untested.