After spending a lot of time and $$ installing channel, extra rock, insulation everywhere, and skipping recessed lights for sconces - I have a big acoustic weak spot in my basement theater.

The vent!!

The square metal duct runs on the bottom of my joists and I have a vent coming off the end which funnels down into the room.

Sounds just go right through the vent. I even have insulation wrapped around the outside of the vent and it doesn't appear to have made any difference whatsoever.

Higher frequency sounds seem to work their way right up the run to the first floor family room even though there are at least 2 90 degree turns.

Anyone have any ideas?

So far the only thing I can think of is putting some 3M furnace filter paper wrapped just under the vent and I'm not holding out much hope. I suppose it is against code to put accoustical foam on the inside of the vent.

After the grief the wife gave me on not putting in recessed lights (for sound), boy is it going to get poured on. . .

Do you have sheet metal ducts or is it a ductboard. If it is sheet metal, like I suspect, just shove some 1" linacoustic in on both sides as far as you can reach (I am assuming it is all covered up now). I believe there might be some code requirement that says the leading or exposed edge of the liner needs to have some duct butter applied to minimize transmission of the fibers to the airstream but you can buy sprays and pastes that do this.

I would shove some linacoustic in on both sides first to see if that helps any. Just remove the grill in the HT and start lining with it and then do the same in the living room or where ever else the noise is traveling to. You might notice some airflow loss to the rooms since you are creating a higher pressure drop through the ductwork now but I would think it is minimal, you be the judge.

As far as what frequencies it absorbs...I am not the expert here. Someone might even chime in with a better idea!

Ditto the Duct liner, You could have done the whole thing when it was exposed a lot easier.

http://www.jmairhandling.com/pdf/AHS-329.pdf

Also I'm not sure of your layout but if possible seal up that vent and do a take off some where else ad then use an Acoustical flex duct (not just your HD flex duct) give it some bends and bring back to feed the HT. Hindsight is a great thing. You could have sealed it up before you put up the ceiling, cut a take off on the top, ran a length of acoustic flex duct to the other side of the room between a couple of joists and then into theater. It probably would have solved this problem. It might not be too late to do some surgery on the ceiling and do a retro fit. Here is the kind of duct I'm talking about:

http://www.jplflex.com/products/products.asp?CategoryID=1

They do make acoustical louvers but I've never heard of any reports on their use.

http://www.kineticsnoise.com/vibronproducts/louvers.html

Yup, it's the square metal kind.

I think I'll try the linacoustic first. For some reason, when I researched this before I had the impression it could not go on the inside of the vent. I will obviously be limited by my arm's length. Do any of the big boxes carry it or is the a recommended place on-line?

The flexible ducting is actually a good possibility as the last four feet of my soffit is empty and I could potentially extend the run with that ducting by four feet without a ton of effort (comparatively, then ripping out the existing metal). Best part now that I think about it is that I do have some limited access from the backside above the TV built-in to work with.

Thanks a lot for the help and links-

John

Where are you located??

Just try this website...http://www.jm.com/locator/mqlocator.exe?link=find

click on HVAC and then type in your zipcode. Simple. I actually need to get some myself.

My AC guy says that Linacoustic or similar products blow the black fibers into rooms. I want to line my ducts but am concerned having two kids in the house and having fiberglass blowing around. He says it does this even with a proper install.

Anybody hear similar things?

By the way, he ended up buying the 1/2" linacoustic. I hope it works as good or as close as th 1". Not positive I will be going with it though based on what he said.

Obviously, if you were to have a separate system for the basement, I guess you wouldn't need it at all. My concern is having noise from the basement traveling upstairs to the first floor thru the vents.

http://www.jmairhandling.com/pdf/AHS-390.pdf

Let's assume he bought the coated kind and will install it according to MFGrs guidelines of treating any cut edges with a coating. He should have got the 1 inch. a 4 x100 ft roll is $125

I could go out and buy the 1" kind today if you think it would make a big difference. He didnt' really know which one to get as doesn't usually use it because of what he said about the black stuff coming thru the ducts.

I have an account with the supplier. It's a little over $200.00 though. I don't really care about the money. The AC guy is going to line the first 10 feet of the supply and return coming out of the air handler. There will be insulated flex supplying the basement but straight pipe supplying the first floor. The entire basement will be open for theater, music room, etc.

Do you have any comments BIGmouthinDC on any other things that could be done to help with AC isolation. He will be installing canvas connectors on the supply and return of the unit and vibration isolators on the unit.

I ended up buying the 1 inch stuff today at a cost of $194.00. Could you post a link to the manufacturers guidelines for installation? I couldn't seem to find on JM's website.

BigmouthinDC you found 1" linacoustic for $125! Lucky!

You can get some mastic such as this...Foster Weatherite Mastic (http://www.fosterproducts.com/default.aspx?PageID=details&pid=125)

Just seal the leading edge where you cut it and you shouldn't get any more fibers in the air than with normal fiberglass insulation in your home.

You have to remember that this insulation's main purpose is for installation inside ductwork to kill sound!

From the Linacoustic RC Product sheet


Installation
Linacoustic RC installation must be performed in accordance
with the requirements of the NAIMA Fibrous Glass Duct Liner
Standard, or SMACNA HVAC Duct Construction Standard. All
transverse edges, or any edges exposed to airflow, must be
coated with an approved duct liner coating material, such as
Johns Manville SuperSeal® products.

http://www.naima.org/pages/resources/library/pdf/AH124.PDF

That's exactly what I was looking for. Thank you so much. I hope this ac guy will do the job right. He's seems very competent. I guess I'll have to watch him closely, though. Installation of this product seems to be very important.

That's exactly what I was looking for. Thank you so much. I hope this ac guy will do the job right. He's seems very competent. I guess I'll have to watch him closely, though. Installation of this product seems to be very important.

In the commercial industry, air quality has been an increasing concern. There was a time when a poorer grade of lined fiberglass was used in ductwork. The fear of glass fibers in the air stream was great and justified. Manufacturers increased the quality of the membranes used to cover the fiberglass which was difficult.

The problem was how to create a membrane that allowed the characteristics of fiberglass to reduce the noise transmission in plenums (which were essentially echo chambers) and prevent the release of fibers which were deemed a significant health risk. Also the membrane had to withstand turbulent airflows and high duct velocities without breaking down over time.

Some manufacturers went with a closed cell foam liner instead of fiberglass which was perfect for air quality but had poorer acoustic properties. It was a compromise. Another concern was methods of fastening the fiberglass liners to the ductwork. The typical fasteners were large washer-like pins that punctured the membrane and got welded to the duct. One issue brought up was that air could still cause fibers to be entrained into the airstream via the punctures so a new fastener that also utilized glue was developed. The glue would melt during the weld process and seal the puncture and provide a better hold of the liner to the duct. I believe the problem only occured when duct velocties were too high.

The point here is that proper application and the use of good quality materials will yield excellent results. Some contractors take short cuts and you should make sure that any contractor used to install a product is familiar and experienced with the installation of that particular product that you are having installed. Some products are more specific with their installation requirements than others.

Also keep in mind that if dealing with a return plenum, this air will pass though a filter (hopefully pleated) which should capture all fibers in the return air stream (assuming that the filter box is constructed well). Supply air plenums are the real concern.

Well it looks like he did a nice job. Everything lined with 1" linacoustic RC. My only concern is that he didn't use mechanical fasteners. He spray glued liner and used the sticky pins to hold liner in duct. A little concerned that the adhesive pin fasteners used to hold liner in place might lose there ability to hold liner in place over time. We'll see.

How does it sound?

They're not done yet and I won't be using any AC this time of year in NY but I should be able to get a decent idea when I get to play some music down there. Will let you know. Also the basement needs to be finished, framed, sheetrocked, etc.

Sorry to bring this thread back...

My soffit and ceiling is still framed and exposed, so this is the time to ask ;)

My whole HT room will be DW+GG+DW. The weakest posint in my opinion is going to be the 2 air vents that run to the whole house furnace. I believe the sound wil get through the vents and end up in every single room in the house!

So, if Linacoustics is the solution (is it?) do I apply it INSIDE the duct, or is this something that gets lined outside the duct? It wasn't clear to me whether the inside lining was a last recourse for those that had already finished/dw the ceiling.

Thanks a lot.

Sound traps which go inside the ducts will eliminate the problem permanently.

The only way to effectively eliminate sound travel through the ductwork.

P.M. me and I will show how to make them and even test the end result. We use them in our sound room and for our projection test room. ;)

The mufflers or "traps" described above work; however, if you're using lined ducts and have at least 4 90 degree turns in the ducts between the room and the air handler (with NO other trunks), it should work just as well.

Now, while we're on the topic, have the HVAC contractor properly figure the load for the room (both sensible and latent heat) ... you'll be surprised at numbers reaching a ton to a ton and a half ... , oversize the ducts and diffusors (supply and return). The contractor should calculate the CFM and then size the diffusors so the velocity at the diffusor is not more than 250 FPM. The room must have both supplies and returns.

Sound traps which go inside the ducts will eliminate the problem permanently.

The only way to effectively eliminate sound travel through the ductwork.

P.M. me and I will show how to make them and even test the end result. We use them in our sound room and for our projection test room. ;)

So, does this go also in the 'opening' of the duct, hence effectively acting as a barrier for sound not to get in through the vent? Or does it only line the ducts and not the opening? If it is the later, then how far down do you line the duct?

I just can't understand... if the sound can get in through the vent, then surely it can continue travelling through the same path as the air, and all the way to the other vents... Sorry, Im not being a skeptic, Im just trying to understand the theory behind this so I can apply it properly if I decide to go with it.

So, does this go also in the 'opening' of the duct, hence effectively acting as a barrier for sound not to get in through the vent? Or does it only line the ducts and not the opening? If it is the later, then how far down do you line the duct?

I just can't understand... if the sound can get in through the vent, then surely it can continue travelling through the same path as the air, and all the way to the other vents... Sorry, Im not being a skeptic, Im just trying to understand the theory behind this so I can apply it properly if I decide to go with it.

Don't think of sound waves as air. They will bounce around in the ductwork because they travel in lines. Unless you have a straight line from the source to another room through ductwork the sound waves will have to bounce around in the ductwork to get to the next room.

The idea with the Linacoustic is to line the duct with a sound absorbing media to kill the bounced sound waves.

Definitely don't cover the supply register with Linacoustic or you will not get any airflow to the space. Line the supply ductwork completely if you can, or at least as much as you can reach. You will have to do some testing to see where it stops helping you in your situation.

Greg,

Thanks, that makes a lot of sense. So, how on earth do people line the interior of the duct? Mine is already 'in place'. Sheetrock goes up in a few days... probably don't have time to react and get this done :( I can't even find Linacoustics locally. Oh well!

Where are you located??

Just try this website...http://www.jm.com/locator/mqlocator.exe?link=find

click on HVAC and then type in your zipcode. Simple. I actually need to get some myself.

Try the link above to find a local distributor. Should be anywhere from $125 - $175 for a 100' roll of 1" thick Linacoustic.

Usually they would nail the liner to the ductwork but if you don't have access to the ductwork I would think you could use some 3M adhesive to spray the liner and then slide it in and press down.

Greg: I imagine that if you just try to slide it in through the vent opening,. you won't get that much in there... an arm's reach, and that's it. Enough?

You would be amazed at how far a little bit goes to help with sound reduction. Do it for all the vents in the rooms that you are concerned with as well.

It obviously won't be as good as having lined ductwork throughout but it will be better!

OK, will give it a try. I clearly won't need 100 feet of this stuff though! :(

Put your location in your profile so people will know. Most people who buy 100' don't need it all and end up storing it for awhile or just tossing it out.

Maybe someone is close enough to you to let you pick it up.

Not a bad idea... updated with my location! Let's see if I get lucky :)