Sound Insulation

[shake777]

We recently bought a new townhouse that needs good sound insulation for both the rest of the house from the HT and for the neighbors from the HT. There is currently a firewall between the two units.

Please let me know of materials that you have used that are both effective and cost effective. The room is currently bare cement walls and about 16X18. Thanks, Nic

[Groomlakearea51]

Bare CBS walls... Consider 1" wide by x 2" deep vertical strips about 12" apart and R13 or R23. I'd also look at sealing the walls before applying the insulation, and subsequently the drywall.

Since the walls are bare at the moment, now would also be a good time to consider a "splayed" wall. What I mean is that the width along the long wall where the HT primary stuff will be is somewhat shorter than the back wall. Easy day because when you apply the insulation, start the vertical strips at about 6" deep and gradually decrease the depth from 6" to 2" as you approach the back wall. Reduce it about evenly about 1/4" each foot as you go. In the front 3-4 feet you would double up on the insulation.

There have been volumes written as to the positive effects, etc. Same thing fror the ceiling. Sloped down towards the HT wall about 6" less height than the rear. I did this with the "man cave" when I was building it, and the difference between this room and other "box" rooms is readily (as in audibly) apparent, and sounds much better than any other room of similar size in which I had the speakers and equipment. What you are doing, in effect is creating a "horn" or mimicking the design of the great concert halls.

Interestingly, as long as you don't get "radical" with sloping and splaying, it's not that noticeable (except the ceiling which my wife has become accustomed to and no longer gives me the "Eye Of Sauron" look...)

The treatment and the splayed design cuts down on reflections, upper long wall corner "bass traps", and outside the room, the sound that does get out will be far less distorted, thus less annoying.

It would be some work, but would probably cut it down to an acceptable level, and would sound quite good. Not really much more expensive than conventional framing, insulation and drywall, just requires some extra insulation and additional "ripping" of some fir studs.

You can "go nuts" as discussed in the Forum section in various older threads, but it becomes a cost vs benefit issue at that point.

Just some thoughts.

[H]

[shake777]

Thanks for all the good information. As you know my main purpose is to keep my sound in my listening area and not in the rest of the house or the neighbors. I'm sure my builder will have no problem understanding what we are trying to accomplish as he seems pretty sharp. I just want to be sure he knows how to do what I need done. Thanks again, Nic

[garyeanderson]

I was working at a new house and the exterior walls were all framed like the diagram below except for the double 5/8 inch sheet rock. The idea is to keep the cold exterior surface from transferring the cold through the siding to the studs and then into the interior walls to radiate. I don't see why it would not work for sound. The double 5/8 inch sheet rock is just a good idea to dampen the sound, My friend helped sheet rock a sound studio 30 years ago and all walls were double 5/8" on both sides. Anyway the diagram is a top view looking down from above the wall, the only parts of the wall that have any contact from one side to the other are the top and bottom plates. Comments are welcome...

[shake777]

My first concern is the cost. But then again you get what you pay for and sound insulation is very important to me since we will eventually have neighbors and I have two RT12d subs. Also you mentioned that this is mainly for temperature insulation and are not sure that this will work for sound. I'm wondering if this is exactly what I want. I sure thank you for taking the time to advise me and I will let my contractor look at this and tell me what he thinks. Thaks, Nic

[garyeanderson]

Hi Nic

I think the double 5/8" sheet rock is a good idea, it's not my idea anyway. The staggered stud wall layout isn't mine either but I think that is may help stop the sound transmission between the neighbor and you. Insulation, sheet rock, and a few extra studs are relatively cheap, Labor to install may not be quite as cheap. Law enforcement at your door at 2 am may not be quite as inexpensive depending on the yes sir, no sir that you may give and the condition you are in to give it. Besides you’re not my neighbor (lucky for you)...

[WMcD]

You should read up on the concepts. One starting point is http://soundproofing101.com/

Regarding room to room transmission, you should get a good concept of how sound is transmitted.

One way is that sound hitting a wall in room A will be the wall in room B if there are studs connecting the walls. It is a mechanical link. That is why so many people suggest that there be staggered studs. But I'm not sure what fire codes say about this. We don't want a chimney for a fire within the wall, The hoizontal pieces in wall construction are to prevent this.

The other point is to stop the wall from moving in response to the sound pressure upon it. That is mostly a matter of mass. Newton's F=MA tells the story. More mass, less A. If you have a fire wall, it may be concrete or brick and that is very good because of mass. Doubling up on wallboard is a step in the same direction. Really, your firewall may the sufficient in the transmission via wall movement.

The A part of the equation is important too. High frequency sounds are essentially high changes or much A. Therefore it is difficult to move a heavy wall with or at high frequencies (same thing) but more easy to move the mass at low frequencies. This is why you hear throbbing bass from the music nut next door. Or in this case, why the neighboor hears throbbing bass from your sub -- you being the nut next door. Smile.

It is also true that sound gets into the next room simply through holes. That is why people suggest sealing off electrical outlets which otherwise allow a path, and putting air tight seals on doors.

We're used to thinking that bats of fiberglass are barriers to sound. Not quite. Looking at the physics, it takes very great thickness of fiberglass to absorb low freqs. Measured in feet, not inches.

The other issue regarding the folks next door is windows. When open, of course they are just open holes for transmission of sound. When closed we are relying on the same concepts as with walls. Double pane glass works better because one pane is not mechanically linked to the second.

The above may give you some realistic ideas. I do think that in the firewall, you may already have a good solution to that part of the problem.

Wm McD

[DrWho]

I was working at a new house and the exterior walls were all framed like the diagram below except for the double 5/8 inch sheet rock. The idea is to keep the cold exterior surface from transferring the cold through the siding to the studs and then into the interior walls to radiate. I don't see why it would not work for sound.

This is actually one of the best methods for acoustic isolation. Ideally there would be no mechanical connection between the inside and outside, but that's obviously not very practical. You just gotta make sure that any time the inside and outside walls are mechanically connected, that the joint is extremely rigid and ideally is load bearing, which adds a lot of mass/intertia to minimize vibration transmission.

Keeping the trapped airspace in the middle as airtight as possible is actually far more important that having insulation...I believe that's also true for thermal conduction too. Anyways, this means you need to seal your electrical outlets and pipes and everything running through the walls.

[shake777]

I have to first say thank you to the responses. I'm realizing as I noted earlier that the essentials of insulation are over my head. I'm going to need help from someone on site to interpret what you all have stated and seem to be in general agreement is the best way to go. I really don't want to deal with angry neighbors, or much worse, my wife when she's bent out of shape. Thank you again for giving me what looks like a great solution to my problem.

[Colin]

With staggered studs, you can put Acoustiblok in the walls.

http://www.acoustiblok.com/theater.php

[shake777]

Thank you for your suggestion. This kind of thing is very much outside my realm and I will be considering each suggestion carefully with a trusted contractor.

[shake777]

Thanks again. The acoustibloc looks very promising.

[Colin]

Most soundproofing techniques don’t attenuate the low
frequencies. Yet it is the deep bass that transmits and penetrates through
walls.

The highest STC rating ever achieved for sound deadening
construction by the independent Architectural Testing laboratory is STC 85!
This was accomplished by using two layers of 16-ounce, black Acoustiblok sound
proofing sheeting, two layers of CertainTeed’s Thermafiber Sound Attenuation
Fire Blankets and two layers of drywall, secured with two sets of steel studs
on both sides of a concrete block wall. In other words, double layers of sound
proofing enclosing the blocks inside. This configuration stops more than 99% of
sound! It dramatically blocks low, middle and high frequencies. Sixteen ounce
Acoustiblok is only 1/8” thick, the same width of two quarters.

The next best wall configuration still blocks 99% of
sound. Using just one layer of Acoustiblok, Thermafiber, drywall and steel
studs on one side of a block wall accomplishes an incredibly high STC of 71.
See http://www.acoustiblok.com/uses.php

[shake777]

Its amazing to get that kind of reduction. I'm waiting for a quote on the accoustiblok materials.

However, as noted above, my best hope is in the firewall. I took a visit to my neighbors yesterday with my system turned up a little. You could have knocked me over with a feather as there was no, none, zip, noise from my place. That's with the subs at moderate volume. I'm totally relieved although I do plan on spending a goodly amount so I can crank it up when I want.

Thanks again for the help. Nic

[Pete H]

Hi Nick, You have gotten some wonderful information and hopefully this will add to your choices and give you some additional information. I'm using the green glue and some of the clips in different applications and have another contractor friend that has used these materials with very good results.

http://www.greengluecompany.com/

[bigrfish]

I had the problem of disturbing my neighbors through a common wall.
After much research I applied a second layer of 5/8" of sheetrock with a
liberal coating of the Green Glue acoustic treatment and surprisingly it took about 6
quarts of their acoustic sealant, which is a different product, to stop up the holes that were there.
After I removed the baseboards, I first piped the sealant material underneath
the lower edge of the existing sheetrock wall until it squirted out
somewhere, much the same way as one would lubricate a car via grease
fittings (remember those?). I took off the electricity and cable TV
outlet covers, and pumped the sealant into the boxes and filled them
totally full of the acoustic sealant (which, when dry, does not conduct
electricity...checked it with a multimeter and it is definitely not
conductive of electricity...also wrapped the terminals on the AC outlets
with plastic electrical tape before the sealant was installed). The
sealant is a little wet and it certainly is heavy, and it has the
tendency to slump and fall out or slowly flow out of a hole like an AC
outlet, so it was necessary to poke it back into the hole when it got a
little dry, kind of repositioning it before the next round of
hole-squirting. It took three rounds of caulking to get those holes
completely filled up where the sealant was not drooping out of the void.
I got extra long screws to float the outlets out to where they would be
flush with the new wall. Next, after the new wallboard was installed, I
went over all four edges with the sealant and formed and shaped the
corners with my fingers and the sealant became my finished interior
corners between the new and existing walls, ceiling and floor. I was
surprised at the amount of sealant it took to do the job. The next step
was to use an industrial-grade acoustic barrier paint, two coats, on the
interior surface of the sheetrock. This paint uses ceramic microspheres
in a viscoelastic vehicle, similar to the design/formulation concept of the Green Glue. See http://www.hytechsales.com/prodsc.html
for more information.

I have not yet checked with the neighbors to see how all this worked, but, Bless God, I have done what I can do to get things to where I can enjoy my stereo without worrying so much about disturbing them. Now that I have shown this good faith effort they may be less likely to complain if they do hear something. One interesting side note is that after I put up the sheetrock with Green Glue my fancy dual-range stud finder would not work on that wall any more, which bodes well for the project. I did this because turning down the stereo and/or walking on eggshells was not an option, at least initially.

Good luck with your project, Chuck

PS I have 6 quarts of the sealant left over which you are welcomed to for the price per tube I paid for it, plus Fedex shipping. It is a half-case of the material. You will need an elephant-sized caulking gun apparatus to apply it.

[shake777]

Thanks Chuck for your detailed response. I noted a common theme between you and I and that's the fact that you are sincerely concerned about your neighbors being able to enjoy the peaceful sanctity of their home. I respect you for that and it certainly seems like you've taken pain to see that you will be able to enjoy your avocation without guilt. I hope this does the job.

I turned my HT up to what I thought was a pretty loud and potentially intrusive sound level. I then knocked on the door of my neighbor and told hem of my concerns. Much to my surprise, I couldn't hear anything from my system leaking into their home. What an incredible relief. It seems that firewall between our units also serves to insulate us from sound transmission as well. The laughable thing was they (a sweet couple about 70 or so) were concerned that their old CRT TV would be annoying me. They do play it loud but, as well, I can't hear a thing.

Now my concern is focused on my wife being disturbed in our bedroom where she enjoys TV. The problem there is the heating registers (forced hot air). I haven't the slightest idea how to stop noise from comming through those vents. Any help here would be appreciated. Best to you, Nic

[bigrfish]

Nic,

Thank you for your very kind and sensitive comments. Let me confess that I did this for some selfish reasons, too, just not wanting to be bothered with the hassles that happen when one disturbs ones' neighbors.

It is kind of extreme, but the acoustic paint may help. It is about the same thickness as mayonnaise, and is not easy to work onto the walls with a roller, but with diligence it can be done. It coats several times thicker than regular paint, and my 15 X 8 wall took exactly a gallon to cover with one coat using a short-nap roller. After the first coat, my curiosity got the better of me and when it dried I did this little test, simply putting my ear against the painted wall and then tapping on the wall out in front of me about a foot and a half with the end of my finger. I tried the same test on the adjacent untreated wall and the loudness of the tap AND the resonance from that stimulus were reduced by about a half to as much as 75% I would say, subjectively not measured. The second coat made it even quieter, so the paint, even though pretty thin, does add something to the mix. It's a little here, little there kind of game, which is "won" at the margins.

Somewhere in your structure there is a course for the HVAC ducts, maybe a soffit-type design. It might, and probably would, help to paint over the area where the ducts run to limit transmission of sound, and actually painting the ducts themselves might help, but the most logical place to start is the first solid structural plane the music, and especially the low frequencies, interact with and treat that surface to reduce what actually gets into the ductwork and then piped all over the house. Heavy bass is the hardest to contain.

The 5/8 sheetrock and Green Glue solution is the best for treating existing construction. The stuff has to really be applied heavy for absolutely best results, but it also works better or at least not-less-well if there are some places that are not covered totally by the product as the wallboard is screwed up into place. (Here's a hint...instead of using phillips head drywall screws, use star-drive head deck screws to put up the sheetrock if you go that route.) About a quart and a half per 4 X 8 sheet is the right level of coating, and you just squirt it on relatively uniformly yet randomly and let it set a little bit so it won't slump and run off as you erect the piece of work.

The paint may provide just enough damping to help, and on the floor above, if it becomes necessary, interposing between the carpet and the subfloor a layer of Green Glue under a layer of MDF or OSB, maybe to a lesser extent a layer of plywood, would be the treatment of choice.

The paint, after being applied, dries with a relatively rough surface, but should not be sanded or smoothed, as the micro peaks and valleys serve to further the goal of sound damping. I'm guessing this paint should be the first thing to do to keep from disturbing your domestic tranquility.

Another trick is to decouple the subs from the floor. Harbor Freight Tools sells some interlocking foam rubber sheets that are typically used to make a resilient walking and standing surface on the floor. A package of those under the subs, or some other resilient material, would help the situation. LF is hard to control and contain.

Women respond to things like flowers, cards, chocolates, and whispered "sweet nothings" better than they respond to technology, so you have your secret weapons to call upon in time of need, just like Popeye and his spinach. Then there is prayer....

Blessings, my friend, as you slay this dragon. You will have excellent results if you don't give up!

Best regards, Chuck

[shake777]

My biggest problem is keeping the sound from traveling through the duct work into the master br and bath. Any solutions? Thanks

[Gilbert]

We recently bought a new townhouse that needs good sound insulation for both the rest of the house from the HT and for the neighbors from the HT. There is currently a firewall between the two units. Please let me know of materials that you have used that are both effective and cost effective. The room is currently bare cement walls and about 16X18. Thanks, Nic

You have cement walls, as in cast-in-place walls? How thick?

Concrete walls are about as sound proof as it gets, no ifs ands or buts about it.