Axiom Home Page Forums General Discussion Home Theater advice on HVAC silencing

I am building a home theater area in my basement, and am considering the following prior to framing and drywall for sound proofing. Any advice/comments would be appreciated:

1. Small heating ducts leading to heat registers in basement and to other areas of the house upstairs - replace straight metal 6" heating pipe with flexible aluminum 5" pipe and create an S-like pattern within the joist space in the basement ceiling.
2. Taking R-9 insulation and using adhesive to stick it to two sides (upper and one side) of hot and cold air returns to dampen the sound (I've heard doing it on the inside is better, but I'm not about to take them apart).
3. Roxul Safe&Sound 3" insulation thoroughout basement ceilng joist spaces and in any gaps in ceiling).
4. Installing resilient channel (sound bar) to joists above home theater area so that ceiling drywall can be attached to it (creating 1/2 inch gap between drywall and bottom of joists).

Thanks,

Take everything below with a large grain of salt; here I'm going from distant memories, party conversations and things I read on the Internet, not hard experience :

I'm iffy on #1 -- going to a flexible duct normally means more noise being generated by the air flowing through the duct, since the inner surface is not as smooth as the plain duct.

There are two different noise sources at work here -- you want bends in the pipe to reduce noise from the HVAC equipment itself being conducted through the pipe to your vents, but you want smooth, slow airflow (big ducts) to minimize noise being generated in the ducts by the airflow. What is the primary source of HVAC noise right now ?

re #2 -- just curious why top and side rather than bottom and side, since your HT will be in the basement. Unless you are using something heavy and solid, aren't you primarily going to get sound reduction by interposing the insulation between duct and HT area ?

re #4 -- sounds good although I haven't actually seen anyone use isolating bars on the ceiling, just the walls. Is the intent here to control sound from the HT leaking up into the rest of the house ?

I used regular paper backed sound reduction fluffy insolation from menards and stuffed it in between all the ceiling raftors. As long as you drywall/finish the basement, I'm nut sure wrapping something around the duct work is going to help much, sound will still travel through the vents a little to the upstairs, unless you cover the vents.

Primary concern is sound isolation in the basement. Ideally I don't want any sound travelling through the rest of the house.

Putting on the upper and side and not the lower is purely to allow more ceiling height, as the drywall would not be able to sit as close up to the returns.

I've heard the purpose of putting it on the returns is just to have something heavy on the returns so they don't have as much of that tin noise (i.e. when I just tap the return now you can hear it right up through the vents, but by putting something dampening like that on them it will deaden the sound through them).

Noise from airflow should be an issue as I'm stuffing safe&sound in the ceiling joists and around the s-shaped pipes. Could be a concern for heat flow though to the rest of the house.

Reduction of mids and highs will be greatly reduced,not much will do anything for sub LFE.

You could get a wussy sub

1st get the sub you want you dont have to turn it up all the way. i think if you use the isolation bar to float the ceiling on the studs and maybe a second layer of sheetrock you may tame the LFEs by a decent amt. but you have to remember your side walls are connected to the house as well so if they are not "floated" lfe will vibrate through them as well.**warning i am not an expert by any stretch this is based on things ive read while researching my ht.**
Jake

I was not at all serious about the wussy sub. It would totally change the sound. The sub output will be less affected by your soundproofing than the higher frequencies (you need thicker insulation to absorb lower frequencies) but if only the sub noise is getting out then you will find it is not as annoying in the rest of the house as you might expect since it's harder to notice without the rest of the frequencies.