The Plains Theater - Page 19

Not thinking wring, but we're normally looking at insulated flex + R13. wrapped around, or as close to that as possible in the space provided.

Less insulation can be offset with longer runs

That sounds great. Please keep taking the great pics!

I am following this HVAC and soundproofing talk closely.

JPA I am sure it is somewhere in your thread but why did you go with a joist muffler instead of a soffit muffler? You mentioned that you are very concerned with keeping sound in and I am sure after talking with Ted he told you the same thing that he told me about the superiority of the soffit muffler for this purpose. With a joist muffler I am really worried about puncturing the sound envelope before the muffler has done its job and the sound going directly up into the floor above just as you stated.

Soundproofing concerns aside I am looking into doing the joist mufflers like you because of HVAC concerns. I just don't think I will have enough space to put my ducts. Is that why you are going this way as well?

One strategy I have given thought to is simply lining the entire joist with dw just as you have done and then lining it with 1-2" of OC 703 and maybe not on all sides. This would provide quite a bit of rectangular cross section for good cfm. And if you have 19' of length I would think that the sound would have enough distance to bounce into the fibers several times as long as you are making a few 90 degree turns along the way.

What do you think?

btw I might have been someone who was talking about keeping sound out for a low noise floor but in the end I know that a theater that I cannot use while the children are asleep is going to be a very frustrating experience. So I am concerned with both.

I wouldn't use unfaced 703, as the fibers may be dispersed with the airflow. FRK may be an idea worth exploring.

No problem at all. And I really do care about preventing sound getting out.

Regarding FRK. So I think that is the kraft paper faced insulation. This is commonly used as DIY sound treatments where one would desire reflection such as between the surround speakers. I plan to do this myself.

The problem I could envision is the high frequencies just bouncing around the muffler without being absorbed. I don't know exactly what frequencies pass through the kraft paper and which are reflected.

Anybody have experience with this?

Is FRK the same as Kraft paper?
Edited by jedimastergrant - 11/10/12 at 6:18pm

I wonder if one could use JM Linacoustic? I will be treating my front wall with it anyway.

This page says it is treated with a resin that should prevent the fibers from becoming airborne and is supposed to be used as duct liner in the first place. As long as the absorption characteristics are favorable it should work.

http://www.jm.com/insulation/performance_materials/products/AHS-329_linacoustic_rc.pdf

-or what about using the denim based cotton insulation?

Linacoustic was designed for lining the interior of ducts, so absolutely it could be used. However, if I am understanding the absorption coefficients correctly, 1" of 703 FRK is a better choice.

Maybe a combo of some sorts would work, but that is well beyond my understanding.. if it's a good idea at all.

Tim

How close is this in-joist duct that you are constructing to the HVAC equipment it is connecting to? And how far is the output of the supply from the exit of the room?

I think the in-joist duct silencer may not be necessary at all and in fact can be a bit detrimental, as Ted mentioned. If you have an in-joist silencer constructed of nothing but hard surfaces directly attached to the structure, you are essentially building a drywall "drum" that has the disadvantage of sound getting transferred (and possibly amplified) into the floor above . . . and all done in the name of capturing sound trying to escape the room through the HVAC.

If you are not too far along in the process, I would not construct the in-joist silencer and just run the flex line as normal, especially since you have double drywall above and a shell with clips and double 5/8" with Green Glue yet to come.

If you think of how difficult it would be for sound to enter through your HVAC supply and navigate all of the twists and turns contained within 19' of flex line to get out of the room, you can see where building a "drum" of drywall behind the shell may not be the optimal tradeoff.

Interested to hear your thoughts.

The Joist Muffler does not have decoupled surfaces, which makes this the least desirable option amongst soffit mufflers or Dead Vents. There are a lot of times when running a muffler through a joist is all you can do, however. Certainly no amplification, as the system has significant added damped mass and absorption. They work well.

That's exactly what I am talking about - it is the least desirable option. My point is there exists a tradeoff between trying to capture sound escaping the room by using an in-joist muffler and the sound leaving the room through normal sound waves.

Given the size of the supply opening, the number of twists and turns in the supply path and the overall length of the supply I really don't think there is that much cause for concern that an in-joist muffler needs to be constructed to capture sound leaving through the supply at the expense of constructing a hollow, uninsulated cubic volume that lacks decoupling immediately above the ceiling.

I would think the insulation of the flex duct would completely fill the space within the joist providing for at least two layers of insulation within the joist and its length, position and pathway essentially eliminate most sound from leaving in the first place. It just seems like a lot of effort for something that may not have any payoff at best and provide a less optimal solution at worst.

"...the opening in the theater." That's my concern. That initial opening(s) for supply and return. I always ask when a sound wave exits those openings, what framing structure will the vibration enter?

So in this case it is entering into a hollow drywall volume (lined with ductliner) that is directly coupled to the structure of the room above (albeit one side of this volume has two layers of drywall with Green Glue). The other case has a volume filled with a thick flex duct and the same two layers of drywall with Green Glue.

Aside from supplying at the front (or front-ish) of the room, you should be returning at the rear of the room. Without going through all the pages of this thread again, if I recall correctly it was not possible to return from the rear - is this correct? Having the return and the one supply so close will create its own little "microclimate" as the conditioned air from that supply will be drawn straight to the return without the opportunity to mix with other air in its room.

Regarding the short soundproofing discussion from this morning - were you intending to put the in-joist dead vent where the 90 degree elbows are before the supplies go into the room? I can see using a dead vent for your shorter supply run in the adjacent room, but I don't think you would get much value for your time and effort if you tried to put one in for your longer supply run IMHO.

One word of advice - the Illuminati of this forum recommend rigid sleeves for any shell penetration and flex duct for the rest. My room is very similar to yours....I simply cut the inner flex short and then left enough of the insulation cover so that once I attached the inner line to the elbow I had enough of the insulation sleeve from the flex line to cover the entire length of the elbow and straight rigid piece. You will have to cut the length of the insulated sleeve so ONLY the rigid passes through the shell, leaving only enough gap to run a healthy supply of acoustic caulk around the rigid penetration.

Well, if you have seen my comments in other threads in this forum you will know I am not a fan of dead vents when a fully-optimized forced-air solution is available to be designed and installed. The exception would be if the position of any duct is very short to the outside of the room or the HVAC system - then I am fully on board with using one as a muffler to isolate the sound either escaping the room from the audio system or entering the room from the HVAC system.

Having the ERV is an interesting option...but wouldn't that simply connect directly to your HVAC system's main return air supply line to introduce the fresh air?

Can you box out a small area of the bedroom or game room and put a small dedicated AHU in there? It seems like your design is getting complicated.

Is the duct on the left side of the picture in post 558 the return?

I feel your pain.. I planned and planned and planned.. and when I went to fit the pieces together.. well.. it did not go as planned.

As long as you can get a good dead vent in that closet, I think you have a workable solution. I would use a short piece of flex to connect the diffuser to the pipe coming through the wall.. but I'm sure you already knew that.

Tim

Why would you cap the first 8" line instead of just running it all the way across to the other side of the room, especially since you are CFM deficient? I think that is an easy choice to keep for the room's cooling.

I also think you are spot-on for using the dead vent, but I think it should be shuffled to immediately inside the room or immediately outside the room instead of having several feet of duct before it reaches the dead vent.

I didn't realize your are CFM deficient on the system to the point of not being able to support the two 8" ducts you would typically need for a room that size loaded with people.

My original point was if you run the 8" across the room in between the joists that a joist muffler would not be necessary because of the elbows, the length of the duct and the seclusion of the duct behind a thick, acoustically soundproofed ceiling. My opinion was that it is better to have a full 8" insulated flex duct fill the void of the joist cavity. This way you don't have to mess around with a joist muffler and you have plenty of fiberglass insulation to not only isolate your duct (and deliver conditioned air, of course), but the insulation will also absorb sound. The drywall box of the joist muffler you were constructing seems to have no use or advantage in this situation.

Running the first 8" supply across the room also obviates the need for a separate dead vent in the mechanical room ceiling.

I think this solves all of your issues with the supply, with the exception of the ERV (which I don't where this is connected to your system. Hopefully this is clearer than in my last post.

Wouldn't the 8" hole in your ceiling be dropping into a soffit? Normally the soffits have their own DD+GG+insulation which would help shield room noise from getting into the soffit and up through the 8" hole.

Regarding ERV... I read surprise/complaints about the Trane FreshEffects ERV that it's basically a stand alone system that doesn't talk to the main HVAC blower. The 2 Broans I have are the same way. So you can hook it into your main return if you want, but then you either need to be running your main blower 24x7 (which I don't like because it picks up water off the coils) -or- accept that effective ventilation will be hit & miss. Another option is to connect ERV as a separate loop to ventilate 1 room and let the asynchronously running HVAC system redistribute that air through normal operation. There are other variations. It has a blower in the unit, so you could probably also use it as a booster fan like you have planned for the Panny.