I'm remodeling a bonus area on the 2nd floor of my home to create a room for HT use. I've ran into two different obstacles for sound isolation and was wondering what opinions others have for solutions.

1. The back wall is shared with a bedroom. Hence I plan on creating a double wall for maximum STC. However, there is a 'column' or chase for a flexible air duct for the lower floor that extends into the bedroom. All of the bedroom wall is 1/2" Sheetrock.

I'm thinking I should stuff this area with fiberglass. Then (see red area on picture) put in some blocking and put in a double 5/8" drywall section to seal it off. I'm concerned that I might be creating a triple leaf wall. The chase is about 14" wide by 24" deep. Other suggestions?

My second challenge has to do with a bathroom wall. Inside this wall (see white box in wall in pic) is a metal medicine cabinet. Do to desires by the wife, she would like to keep it so it is consistent with the other bathrooms. It is made of thin metal, and when I was first playing the speakers before work started, it seemed to almost amplify the sound on the other side. This wall will also be a double wall when complete.

So I'm thinking: I have some 1-lb MLV. I can remove the cabinet and glue the MLV to the back and sides. Basically any metal surface not seen from the bathroom side. Then reinstall the cabinet, using drywall and acoustic caulk to fill in the sides. Then put up as much 5/8" drywall on the back of the cabinet (with GG or something similar) while still maintaining a double wall configuration. I'm hoping that it will provide enough mass and dampening to keep the metal cabinet from ringing.

Other ideas?

How about covering the backside of the cabinet with Dynomat or something similar? It's used in car audio installation to tame ringing and rattling.

Besides that I'd just stuff the cavity with fiberglass and double drywall/GG all walls/ceilings.

I'm remodeling a bonus area on the 2nd floor of my home to create a room for HT use. I've ran into two different obstacles for sound isolation and was wondering what opinions others have for solutions.

1. The back wall is shared with a bedroom. Hence I plan on creating a double wall for maximum STC. However, there is a 'column' or chase for a flexible air duct for the lower floor that extends into the bedroom. All of the bedroom wall is 1/2" Sheetrock.

I'm thinking I should stuff this area with fiberglass. Then (see red area on picture) put in some blocking and put in a double 5/8" drywall section to seal it off. I'm concerned that I might be creating a triple leaf wall. The chase is about 14" wide by 24" deep. Other suggestions?

As the bedroom is right across the wall from the theater room, i would plan on double drywalling the theater side of the bedroom as well as the theater wall.

Additionally, i'd opt for a double wall or RSIC/ISOMAX clips on the other sides of the bonus room as well to cut down on flanking noise making its way to the bedroom via shared strutural elements.

Putting fiberglass by the duct is advisable, and the more mass that you put on the theater side of the double stud wall, the less trouble the duct area can wind up causing you.

let me know if that didn't make good solid sense.

dynamat or MLV attached to the cabinet is a good idea. Both will add some mass to the flimsy metal and help keep it from buzzing, etc.

And as you are again planning the double stud wall design, make sure the side of the double stud wall away from the cabinet has double drywall (double 5/8") and that the cabinet has insulation in front of it.

dynamat or MLV attached to the cabinet is a good idea. Both will add some mass to the flimsy metal and help keep it from buzzing, etc.

And as you are again planning the double stud wall design, make sure the side of the double stud wall away from the cabinet has double drywall (double 5/8") and that the cabinet has insulation in front of it.

Thanks for the feedback. Attached is a pic (hope it make sense) of what I had in mind. I'll probably use some spray foam as well. Anything to make sure all the unseen metal surfaces are securly dampened and attached to something that won't let it vibrate easily. All the walls between the HT room and the rest of the house will be double 5/8" sheetrock. Looks like this is about the only way to go :)

As the bedroom is right across the wall from the theater room, i would plan on double drywalling the theater side of the bedroom as well as the theater wall.
The theater side of the wall will be double 5/8". Not sure I'll be able to drywall INSIDE the bedroom closet or outside the duct chase (don't think the wife will appreciate expanding MY project into kids room :D ) The bedroom wall is only 1/2" sheetrock (even though the next side is a closet). Would cutting strips of 5/8" sheetrock and laying between the 2x4 studs on the inside of the wall/bedroom side be effective? See pic.

I guess I can always complete the HT first and see how it sounds before moving construction onto another part of the house. (no loud bass heads live here)
Additionally, i'd opt for a double wall or RSIC/ISOMAX clips on the other sides of the bonus room as well to cut down on flanking noise making its way to the bedroom via shared structural elements.
Flanking noise is a bit of a concern here... or not. ?? The bonus room is entirely over a 2 car garage. And the ceiling is in a roof gable that extends into the main house roof (sans tile). The opposite two sides of the HT are exterior walls. The space between the bathroom and bedroom will be a new wall that is staggered studded (for space reasons). HT Ceiling joist run parallel to the new wall (perpendicular to bedroom) and are separate from the ceiling joists on the bedroom side. I could quite easily seal the attic space above the HT room with a couple sheets of sheetrock (with an access plug of course) to isolate the HT attic space from the rest of the house (?).

The biggest flanking that I see would be the edge of the inside 'false roof' resting on the bedroom load bearing wall and the perpendicular floor joists under the new wall going into the house (about 3 feet worth) and the part where the double wall ties into one of the exterior walls (not much I think I can do about that). Building a room within a room would take up to much space and I would have a walk-in closet HT :p

Note: the floor between the HT and bedroom wall is 3/4" board. Will this really transmit that much sound to the bedroom side after passing under the first layer of the double wall?
Putting fiberglass by the duct is advisable, and the more mass that you put on the theater side of the double stud wall, the less trouble the duct area can wind up causing you.
So would blocking off the duct space creating a triple leaf?

Brian, thanks for looking/reading my rather lengthy description. Hopefully someday AVS will allow mpegs to be posted, with audio, to make explaining things a lot easier :) I hope MY descriptions were understandable. :)

Thanks again for all the feedback you've provided (this thread and many others).

tiggers,

your medicine cabinet idea looks great. I'd strive to get the drywall/gg/heavy stuff in contact with the medicine cabinet to avoid a tiny air space and associated resonance. In other words, something touching the medicine cabinet would be preferable to an 1/8" air space.

The theater side of the wall will be double 5/8". Not sure I'll be able to drywall INSIDE the bedroom closet or outside the duct chase (don't think the wife will appreciate expanding MY project into kids room :D ) The bedroom wall is only 1/2" sheetrock (even though the next side is a closet). Would cutting strips of 5/8" sheetrock and laying between the 2x4 studs on the inside of the wall/bedroom side be effective? See pic.

I guess I can always complete the HT first and see how it sounds before moving construction onto another part of the house. (no loud bass heads live here)

i would - before doing the theater side and losing the chance - do exactly that. add some mass to the bedroom side of that double stud wall. the 5/8" should be affixed to the existing 1/2" with a bead of glue to make sure you don't have small air cavities, etc. But adding mass to that lightweight side is pretty cheap, and pretty painless relative to going back and doing it inside the bedroom later.

Its always quite a luxury to be able to do X, and Y, and then listen/experiment and determine if you need to do Z. But in this case, i'd opt for the few bucks of drywall as you mentioned up front as the possible after-the-fact modifications are much more annoying.

Flanking noise is a bit of a concern here... or not. ?? The bonus room is entirely over a 2 car garage. And the ceiling is in a roof gable that extends into the main house roof (sans tile). The opposite two sides of the HT are exterior walls. The space between the bathroom and bedroom will be a new wall that is staggered studded (for space reasons). HT Ceiling joist run parallel to the new wall (perpendicular to bedroom) and are separate from the ceiling joists on the bedroom side. I could quite easily seal the attic space above the HT room with a couple sheets of sheetrock (with an access plug of course) to isolate the HT attic space from the rest of the house (?).

The biggest flanking that I see would be the edge of the inside 'false roof' resting on the bedroom load bearing wall and the perpendicular floor joists under the new wall going into the house (about 3 feet worth) and the part where the double wall ties into one of the exterior walls (not much I think I can do about that). Building a room within a room would take up to much space and I would have a walk-in closet HT :p

Note: the floor between the HT and bedroom wall is 3/4" board. Will this really transmit that much sound to the bedroom side after passing under the first layer of the double wall?

Brian, thanks for looking/reading my rather lengthy description. Hopefully someday AVS will allow mpegs to be posted, with audio, to make explaining things a lot easier :) I hope MY descriptions were understandable. :)

Thanks again for all the feedback you've provided (this thread and many others).

Hey, you are sure welcome.

It is certainly possible that structural flanking noise via the floor/joists to the rest of the home or the walls of the bonus room to the rest of the home will be troublesome. The Canadian gov't did a massive study on this kind of flanking and the results were informative and wildly technobabblish :D ).

But, perhaps this is something you could do staged work with, as you described above? Put the double stud wall and door in place, then do some noise making/listening to see where you are at?