# HVAC questions on construction



## afeest (Sep 5, 2012)

Started construction on the home theater/music room. I did a lot of research and am building a room within a room design. The early research i did indicated that the best thing to do with the ductwork was to use a spray in it to reduce the sound transmission. However, after recently reading some stuff i had not seen on the soundproofing co. website (was looking to order some stuff there) - i'm thinking i have made a huge mistake on my HVAC. Wondering if should have been building a dead vent (which i don't fully understand the design quite yet) - and i may have taken my expensive home theater design and turned the HVAC system into a giant megaphone - audio supression spray or not. 

Had cold air return built out of complete ductwork - because of the double wall design - and planned on spraying it. I'm thinking my supply side though - which are a pretty short run directly from the furnace - are gonna be the real problem.... 

Any ideas or suggestions on the best way to fix this? I hate to spend 15k building a theater and have the audio traveling through the HVAC cuz i didn't do it right - and didn't want to spend a few extra bucks to fix a mistake when i could.

One pic is of the cold air return in the back of the theater, the other is the supply line coming from the furnace on the left wall of the theater. Just a straight big pipe... me thinks it will be a problem - but not sure what i SHOULD do.

suggestions?


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## NBPk402 (Feb 21, 2012)

I was looking last night for info on soundproofing and came across a video that might be of help to you...
http://www.ehow.com/video_4971322_soundproofing-ventilation.html

This guy has several but this one is on HVAC soundproofing. Hope this helps you.


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## afeest (Sep 5, 2012)

Now that i understand the principle of the dead vent - i was hoping to actually get fresh supply from the HVAC vs. the rest of the basement... 

wondering if it would help to use the principle of diameter restriction - using the same large duct i have there now, reducing it to a 6 inch duct as it nears exiting the room - and convert to a 6 inch flexible duct int the last couple feet feeding into the furnace supply. I could even route that flexible duct so it bends a few times or is longer if that might help....

edit... hmm.. That video looks interesting... wonder if a combination of what i was thinking and his trick would help...


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## NBPk402 (Feb 21, 2012)

In the link I posted... He suggests putting insulation in the tube and inserting several all the way down the tube alternating them to reduce the noise. He also suggests using the largest tube you can.


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## afeest (Sep 5, 2012)

Yes - i noticed that from the link - good idea i think - and i'm thinking it could be as simple as that - and maybe moving to flex duct on the supply closer to the furnace. There is a damper in the current rigid duct right near the furnace - so i'd have to do something there. 

Video was good- thankyou!


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## ALMFamily (Oct 19, 2011)

Would it be an option to convert the feed completely over to flex? With that long of a run, you could put a few bends in it and kill most of your sound transmission.


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## afeest (Sep 5, 2012)

So - after a bit more research - the design changes i've made...

1. Removed the cold air return completely - and will be constructing a dead vent in it's place. That will exhaust the theater air into a larger basement area. That basement area already has FOUR supply ducts and a cold air return across the room - that is only feet from the furnace.

2. Current rigid supply line has been removed - and flex duct will come in from the theater - pop up to over the floating ceiling - across the theater and drop into a new soffit on the opposite side of the theater. This will give me a longer run of flex duct - with several bends in it - and the soffit will be built according to the soffit build guide i was able to get from John at SPC. 

Looking good - now i have to figure out is the vents themselves. I did find something about a larger vent (20 inches plus?) that connects to a six inch round supply line. The idea being to increase the area of the vent - to minimize any whistling... anyone know where i can find these? they look like commercial office registers.


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