Furnace Returns Duct Work

[ChickenSchmidt]

I have been working on the basement getting it ready for paint. I have an armstrong suspended ceiling and the air returns and duct work are in between the floors. All the walls have 2x4 studs with drywall and insulation in between. What can be used to deaden the sound going to the upstairs through the ceiling? I want to do this before I paint and get all the wiring done.

Also at the one end of the room the wall is drywalled but not finished on the other side, the furnace side. All the other walls have concrete and insulation behind the drywall. Probably should insulate that wall but what do I use?? The room is 32 x 15 with an 18 x 11 offset room witch makes it an L shaped room.

I got sidetracked with the equipment end of this project and didn,t take the acoustics into consideration. I went upstairs yesterday for a break and was sitting in the kitchen and could here the music coming up through the floor.

 

[TLS Guy]

I have been working on the basement getting it ready for paint. I have an armstrong suspended ceiling and the air returns and duct work are in between the floors. All the walls have 2x4 studs with drywall and insulation in between. What can be used to deaden the sound going to the upstairs through the ceiling? I want to do this before I paint and get all the wiring done.

Also at the one end of the room the wall is drywalled but not finished on the other side, the furnace side. All the other walls have concrete and insulation behind the drywall. Probably should insulate that wall but what do I use?? The room is 32 x 15 with an 18 x 11 offset room witch makes it an L shaped room.

I got sidetracked with the equipment end of this project and didn,t take the acoustics into consideration. I went upstairs yesterday for a break and was sitting in the kitchen and could here the music coming up through the floor.

Apart from fiber glass insulation, there is not much you can do about it. A good deal of the sound, most of it in fact, will be transmitted by the duct work, that acts as a huge megaphone. To isolate sound you have to go to the trouble of building a room within a room and not using a ducted HVAC.

 

[ChickenSchmidt]

Thanks for the reply. Lots of infomation to take in. I realize I will need room treatments. Just don,t want to have to take anything apart after it gets put together.

 

[highfigh]

You can install a flexible coupler in the ductwork before it gets to the plenum, preferable far from the furnace so the mechanical transmission can attenuate as much as possible. You can also use ducting that is lined with absorptive material or if the ducting from the theater room can't be replaced, a baffle can be installed near the furnace. This is basically a box made of internally insulated duct material, placed at a 45 degree angle to the return and supply air ducts, and with an absorptive baffle in the middle of the box. That way, the sound is attenuated somewhat before it gets to the de-coupler, sound deadening box and baffles. HVAC people hate things like this because they like laminar air flow but this is a good time for a compromise.

If necessary, using a separate blower to maintain the temperature in the theater for fresh air will help and it would reduce the need for attenuation in the supply runs, although the flexible coupler will be needed anyway.

Isolation of the theater room from the rest of the structure is best. The diffusers shouldn't be directly open to the theater room- a flat panel with absorptive material on the backside helps, especially if it's a lot larger than the size of the duct- the sound can bounce off of the ceiling and be attenuated by the material on the backside of the panel, allowing less to enter the duct itself.

 

[bpape]

One thing you can do in addition to insulation is to beef up the hangers holding the track system and cut drywall sheets the same size as your tiles and lay them on top of the tiles. That won't stop everything but the additional mass will help a reasonable amount.

If the ductwork is tin, replace with flex duct where you can and make sure to damp the rest of it so it doesn't ring and in some cases almost amplify mid and high frequency transmission through the system.

Bryan

 

[ChickenSchmidt]

Bpape thanks two very good ideas. May just rap the ducts with insulation.

 

[bpape]

Even if you can only do a small section in flex or duct board, it's hopefully enough to break the amplification chain in the tin.

One other thing you can do up in the ceiling is to use a layer of drywall with Green Glue on the underside of the floor above to help a little more with additional mass and a little isolation.

Bryan