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.

But is it worth doing the whole s-shape in the heating pipes and lining the outside of the returns, or should I just put safe&sound everywhere and leave it at that?

I was in the PHVAC business for 27 years, so I can tell you that you need to be very careful about making changes to your duct system.
HVAC ducts are sized to deliver proper airflow so you get even, efficient heating and cooling. The whole system is sized and designed based on heat loss (winter) and heat gain (summer).
I'd strongly suggest that you get a good contractor to look at your system and evaluate what you can and can't do.
Jack

Typhoon,

The things you are considering will be good for sound isolation.

Modifying your ducting for an "S" shape is recommended by alot of theatre enthusiasts and seems to work well. The more curves sound has to travel through, the less it will persist through the curves. 4 Products from Owens Corning should be sufficient for duct silencing.

Concerning your resilient channeling. There is a better method that has spread like wildfire on the DIY theatre called green glue.

It is more effective blocking LFE than resilient channeling.

If I had known about this product prior to putting up my drywall, I would have used it. When I started my basement 3 months ago, I didn't know anything about sound proofing. I just started the drywalling and THEN i started researching. Should have done it the other way!

In any case, go here for a comparison of green glue vs resilient channeling. It yeilds better STCs and cost benefit is very high. Go down about half way for the GG vs RC discussion.

Double 1/2" drywall on each side of the wall with resilient channel on one side with insulation will yield 45 STC.

Single 5/8" on one side and double 5/8" with GG on the other side with insulation will yield an STC of 52. And its much easier to use I think. Just regular drywalling with a double layer of drywall with GG sandwhiched in between on the sound side.

Check out that website for all the info you needs, its really quite an amazing product.

Below is a chart of the 2 comparisons.



"A comparison of resilient channel and Green Glue assemblies with 3 total layers of 5/8” drywall, taken in the same lab.

The RC was verified by the lab to be 25 gauge (which is appropriate), and it was properly installed.

Note that while the RC, like GG, yields a very good STC, its low frequency performance is far worse. Remember that, in theory, doubling the mass of the wall would cause a 6dB low frequency performance increase, all other things equal.

If the channel was not properly installed, this difference is likely to be even larger"

cool stuff. where do i buy the owens corning material?

also, between these 2 choices (ceiling installation only as all walls are exterior walls)
1. double layer roxul safe & sound insulation (as opposed to single layer only), or;
2. single layer only with insulation, but double layer drywall and use the green glue in between

which would be better to reduce sound from travelling upstairs?

lastly, i was thinking of putting roxul s&s around my air returns, but heard if i wrap them in tinfoil or that reflective tape instead i will get good results at reflecting sound. my problem is i have low clearance under my returns and didnt want to reduce it further with the thickness of the insulation.

It's late and I'm tired so I'm not sure if anyone already posted about staggering the studs... at any rate here's a quick link for you Staggered Studs

>>cool stuff. where do i buy the owens corning material?

No clue, find a local insulation distributor. Or look on the Owens Corning webiste.

>>also, between these 2 choices (ceiling installation only as all walls are exterior walls)
1. double layer roxul safe & sound insulation (as opposed to single layer only), or;
2. single layer only with insulation, but double layer drywall and use the green glue in between


Insulation really has a minimal effect on sound transmission than the drywall or GG.

I wouldn'y spend any more on insulation for sound blocking purposes unless you want more for heat transfer purposes.

I think insulation adds about 3 STC to the total STC of a wall. You don't need to double up on that.

A single layer of insulation with double drywall and GG would yield you excellent results.

Keep in mind that just because your walls are all exterior walls against concrete sound can still transmit through the studs up into the joists.

The poeple at GG recommend doing the whole room with double drywall and GG. Although if this isn't in your budget, doing just the ceiling would give you great results. You can email GG, they are very helpfull.

Staggered studs are also amazing. Like the previous poster said.

A couple of thoughts on this subject, as in my last house, I spent great efforts, money and time building as neutral a room as possible. The aim was soundproofing, as well as being dead - my version of a chamber.

Anyway, on the studs - this is for a non load bearing wall - especially if you follow the link and use 2x2 studs. I did not see that mentioned in the article, but may have missed it.

The essence of all of these treatments is to eliminate sound waves penetrating, or going through the materials. All materials also have a resonance, or frequency at which they will resonate or vibrate. By building with multiple types of materials, the sound waves will not make the traverse completely through a wall/celing/floor, as something in the composition will stop the wave at the frequency.

While it is difficult to tame this, it is not entirely impossible. I used a combination of most of these methods, and as painstaking as it was, the rest of the house rarely had to endure anything noisy.

I would be careful with the load balancing of the HVAC, as it was correctly mentioned that it is a tuned system - or should be to operate efficiently.

Great advice guys.

My real budget I'm working with for soundproofing is going to be about $1700+tax for a 1000sqft open area basement. My main area for the sound is about 15x15, but I realize the actual soundproofing area is much larger than that.

This budget includes any Roxul safe & sound insulating. I know it's not a huge budget, but most of my $$$ is being spent on getting the basement finished and my audio/video equipment.

I plan to only work at sound proofing for noise travelling up through the first floor to the rest of the house, and not so much for deadening the sound in the basement. Also, I have a cold and hot air returns pretty much running over a quarter of the listening area (i.e. speakers right below), with returns leading to the basement ceiling right over the listening area.

Given my budget, these are my scenarios:

Scenario 1: No Safe and sound anywhere; double drywall and green glue in between layers in 75% of basement ceiling, including around HVAC units

Scenario 2: No Safe & sound anywhere; double drywall and green glue in between layers in listening area only; use Owens Corning material to insulate HVAC unit.

Scenario 3: Safe & sound everywhere; no double drywall or green glue; use Owens Corning material to insulate HVAC unit

Scenario 4: Safe & sound over listening area only; double drywall and green glue in between layers in listening area only; single layer no safe & sound over all other areas in the basement

More advice please would be very helpful.

any ideas or advice?

If there is really no way for sound to travel upstairs through the walls of your theatre then due to your budget you shouldn't double drywall the walls of your theatre.

I am not sure of all your options. If you are planning to only cover 75% of your ceiling with GG, it will be not be effective. Look at sound like a fish tank, once there is a leak in the tank all the water starts draining at that leak, the water doesn't care about the remaining areas that don't have a leak.

With that said, you don't really need Safe N' Sound insulation, normal 1ft fluffy pink stuff will work just as well, the safe n' sound stuff is just a way to get more money. It won't really add that more STC to your ceiling.

STC is obtained by adding mass and sound absorbing materials. GG absorbs the vibrations so they don't pass through the next drywall sheet and into the studs.

If you can do it, double drywall & GG the ceiling of your theatre room (especially around the HVAC area) and use regular 1ft insulation in the ceiling joists.

You need to make sure when doing double drywall that you mud the cracks of the first layer and let it dry to ensure a flat surface for GG coverage on your next layer.

goto avsforum.com and search "Green Glue" you will find a main thread with questions and answeres from GG makers.

I recently saw an episode of Holmes on Holmes and he was dealing with sound transfers between Semi-detached houses and the results he had using a system like this, or this system, were very good, dropped the sound levels to below audible levels.

I saw this as well, he really pushed the staggered studs.

The drywall he used was along the same principal but a specific brand that cost 10X the price of regular drywall. It basically was 2 pieces of drywall laminated together with the green glue/caulking stuff.

An interesting thing he mentioned a few times was when nailing in to it to not take the nails out but rather push them in to keep the seal.

Holmes on Holmes Episode

Drywall Installer Used & Product Link

Is it just me, or does that sound like Victorian murder mystery porn?

I just stumbled across the following link, haven't had a chance to read it or anything yet...

http://quietsolution.com