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post #1 of 27 Old 05-28-2003, 03:49 PM - Thread Starter
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I remember hearing from several sources that drywall seams should be caulked, including floor and ceiling, with an acoustical caulk. I can't find a source of any caulking product that specifically states it is for acoustic treatment.

Do you think any siliconized acrylic caulk will do just as well?
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post #2 of 27 Old 05-28-2003, 04:01 PM
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As a newbie myself, I did read about it. Any silicon caulking will work because the basic idea is to stop airflow hence to stop sound "leak".
Best regards
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post #3 of 27 Old 05-28-2003, 04:15 PM
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Acoustical caulk differs from silicon caulk in that it remains pliable over time. Thus, acoustical caulk does not crack or leave gaps as the walls (floors, etc.) expand and contract over time. Acoustical caulk is not available at Home Depot or Lowes (where I live), but is readily available at all commercial drywall supply houses.

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post #4 of 27 Old 05-28-2003, 05:12 PM
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I got mine at www.ShelterSupply.com it is also available online at AcousticalSolutions.
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post #5 of 27 Old 05-28-2003, 07:20 PM
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There are rubberized (silicon) acrylic caulks on the shelf at HD and Lowes that claim to remain flexible for 50-75 years. Since I'm 53, I think that is pretty much a lifetime guarantee. They are $3 ish a tube. Why use the stuff labeled Acoustic?
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post #6 of 27 Old 05-28-2003, 07:48 PM - Thread Starter
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Quote:
Originally posted by BIGmouthinDC
... They are $3 ish a tube. Why use the stuff labeled Acoustic?
I think I agree. I think the 35 yr stuff would be OK by me also.
Thanks for the replies.
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post #7 of 27 Old 05-29-2003, 06:30 AM
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What do you folks make of the precautionary message for the stuff at Shelter Supply?

Quote:
Precautions, follow material safety data sheets for warnings prior to opening containers and during use and storage. Product must be used with adequate ventilation and personal protection and vapors must be prevented from entering occupied buildings.
In particular what do you think regarding the phrase I've highligted in Bold? Would putting this stuff just between the bottom of the sheetrock and floor behind the baseboards satisfy the room's chalking requirements and take care of the precaution to prevent vapors from entering the building? Are the vapors a continual concern, or only during the initial application?

Thanks.

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post #8 of 27 Old 05-29-2003, 07:20 AM - Thread Starter
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I image that's during application, but a call to the manufacturer is always a good idea.
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post #9 of 27 Old 05-29-2003, 09:16 AM
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When building a tight room, there will be gaps that you're actually filling, not just sealing. The advantage of a good acoustical caulk is the mass that it has. Sure you can make a crack airtight with silicone, but low frequencies will fly through. A tube of acoustic cauld is heavy as hell, noticeably moreso than regular caulk and adhesive.

The other benefit of a good acoustical caulk is to "butter" the backs of junction boxes, etc. Making the boxes more dense is one less source for leaks.

So you see if you are trying to achieve extreme isolation, you really need some dense stuff.

Of the several that I've tried, USG brand is clearly superior. Excellent adhesion, pliable, yet very dense. It's perfect. I went through a lot of it and would not ever use silicone, but that's me.

Keep in mind that the total success of the soundproofing is an additive process. These leaks add up to significant square footage. The junction boxes alone in my theater add up to nearly two square feet!

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post #10 of 27 Old 05-29-2003, 09:39 AM - Thread Starter
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Quote:
Originally posted by Ted White
The junction boxes alone in my theater add up to nearly two square feet!

Ted
That's why I designed mine to have no boxes. I have outlets in the riser and pilasters which are inside the room. All lights are surface mount or cans in the dropped ceiling below the drywall. Only holes for wires are cut into the drywall and those will be caulked. Wire holes are alot easier to fill and seal than a 2 1/4" x 4" square cutout for a box.

I think I'll stick with the silicone. I 've used R30 in the ceiling and R19 in the walls, resilient channel, 1/8" limp-mass vinyl sheeting, 5/8" drywall and 1/2" drywall staggering the seams, and no junction box cutouts which is the most important. I'm still not convinced paying double for caulk labelled "acoustical" matters at all once the features listed above are covered. I'll stick with silicone and tape over that -- on both drywall layers.

BTW Ted, great website. I noticed the boxes you built to house the can lights -- good idea.
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post #11 of 27 Old 05-29-2003, 10:33 AM
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Quote:
Originally posted by Ted White
.... but low frequencies will fly through.
Ted
I thought low frequencies with such long wavelengths cannot escape through small cracks and openings. No?

Quote:
Originally posted by RonAuger
have outlets in the riser and pilasters which are inside the room.
[/b]
How did you get away with code?

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post #12 of 27 Old 05-29-2003, 10:48 AM
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Because of their length / energy, low frequencies will actually pass through even better. They bounce more / get absorbed less and will find their way through more easily that higher frequency sound. Higher frequencies are more easily absorbed.

This info courtesy of Chris Collins from CCE.

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post #13 of 27 Old 05-29-2003, 10:53 AM
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Quote:
Originally posted by ArtisTech
I thought low frequencies with such long wavelengths cannot escape through small cracks and openings. No?
Low frequencies will absolutely "escape" through small openings. High frequencies will "diffract" through small openings in thin material (like perforated screens and speaker grilles). Low frequencies, because of their long wavelengths in relation to the thickness of the wall escape through holes unscathed.
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post #14 of 27 Old 05-29-2003, 11:14 AM - Thread Starter
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Quote:
Originally posted by ArtisTech
How did you get away with code?
Putting outlet boxes in risers and pilasters conforms to code provided you use a wire connector. A misnomer, in my opinion. It is a wire clamp that holds the wire as it passes through the outlet box, and usually resists the wire pulling back out of the box. In the riser, I used metal boxes recessed a little into the 2x10. Metal boxes also need to be grounded.

Reagarding the caulk, as long as all holes/cracks/seams are sufficiently sealed airtight (and stay that way over time) the product details are immaterial. If I press enough mud into the crack, that should be adequate also.
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post #15 of 27 Old 05-29-2003, 11:31 AM
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Quote:
Originally posted by RonAuger
Putting outlet boxes in risers and pilasters conforms to code provided you use a wire connector.
OK, I didn't ask the proper question.

According to the code, you should have an outlet within 6' of any openings and 12' thereafter. Hence, not put any outlet on the wall would be a violation! At least that is what I have been advised to do. Your thoughts?

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post #16 of 27 Old 05-29-2003, 11:47 AM
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Ted,
Thanks for your reply.

Quote:
Originally posted by mysphyt
Low frequencies will absolutely "escape" through small openings. High frequencies will "diffract" through small openings in thin material (like perforated screens and speaker grilles). Low frequencies, because of their long wavelengths in relation to the thickness of the wall escape through holes unscathed.
Assuming a small crack in a wall and not sealed properly, the low frequency will escape thru converted to a smaller wavelength. The size of the opening should dictate the up-converted frequency. We are assuming that the wall here is a well constructed wall. Any thoughts?

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post #17 of 27 Old 05-29-2003, 11:56 AM
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I don't think the hole changes the frequency. Chris can explain further.

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post #18 of 27 Old 05-29-2003, 01:43 PM
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The crack (or hole) acts like a new source, the dispersion on the other side of the crack is described by:

sin x = W/D

where:

x = angle from "straight through" where minimum sound pressure occurs
W = wavelength of the sound
D = width of the crack

for round openings the equation becomes

sin x = 1.22(W/D)

The picture below shows two different frequency waves being diffracted by a slot. You can see the lower frequency (longer wavelength) wave in the lower picture "spreads out" more on the other side of the slot.

From the above equations, as the frequency decreases, W increases, and the angle of diffraction (x) widens. For small values of D (little holes), only the lowest frequencies will diffract appreciably.

The point is, the hole won't change the frequency, but the lower frequencies (big W) will propogate widely on the other side of the crack or hole. The higher freqencies will only be audible right in front of the hole.

The old listening at the keyhole analogy fits. If you want to hear a conversation (relatively high frequency) in another room through the keyhole, you have to put your ear right up in front of the hole.

http://www.zainea.com/kdifr.gif
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post #19 of 27 Old 05-29-2003, 02:00 PM
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Nice, but the equation is new dispersion angle of the wave.
If you could provide an equation that represents the new f as a function of old value and pin size then we can find some thing here.

If you consider the port of a speaker, the port should pass all wavelength of the woofer. But in reality, it passes only a certain freq based on its physical dimension as it was tuned by the designer.
Edit:
I just remembered that low frequency below 75 Hz is not directional. Another words, the dispersion angle is 360 degree.

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post #20 of 27 Old 05-29-2003, 03:19 PM - Thread Starter
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Quote:
Originally posted by ArtisTech
According to the code, you should have an outlet within 6' of any openings and 12' thereafter. Hence, not put any outlet on the wall would be a violation! At least that is what I have been advised to do. Your thoughts?
"Code" is really what your county building inspector will or will not accept. You're right in what the code states. But it might be clearer to you why my building inspector allowed my situation if you state the code more accurately this way: "No point along a linear wall should be further than 6' from a receptacle." My riser cuts across nearly the entire room with outlets placed towards the ends. If you draw a 6' radius circle around the outlets on my plan, it "covers" the outside wall that it is near. My building inspectors interpretation allows that coverage even if the outlet is not on the wall. For instance, an outlet on a free standing pilaster 2' from the wall (or a floor outlet for that matter) covers less than 12' of the wall like a wall-mounted outlet does (6' in either direction), but it still counts.

Did that make sense, or did I ramble? Bottom line, ask all your questions of your building inspector, after all, he/she has the final say of what goes.
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post #21 of 27 Old 05-29-2003, 03:23 PM - Thread Starter
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mysphyt,
Great math stuff .. but do you have any images with silicone caulk and acoustic caulk plugging up the slot? :)
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post #22 of 27 Old 05-29-2003, 04:47 PM
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Quote:
Originally posted by ArtisTech
I just remembered that low frequency below 75 Hz is not directional. Another words, the dispersion angle is 360 degree.
Isn't the non-directional quality of low frequencies due to the way humans perceive sound and not the angle of the wave itself?

Art
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post #23 of 27 Old 05-29-2003, 05:37 PM
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Quote:

Originally posted by ArtisTech
I just remembered that low frequency below 75 Hz is not directional. Another words, the dispersion angle is 360 degree.

Originally posted by A. Vandelay
Isn't the non-directional quality of low frequencies due to the way humans perceive sound and not the angle of the wave itself?

Art
Two different things. Low bass below 80Hz or so is generally considered to be non-directional from a hearing point of view.

However, the dispersion angle of sound has to do with the baffle width of your speakers. Depending on the width of the baffle of your speakers, the sound coming out will switch from a 90 degree (discounting horns) dispersion pattern to a 360 degree dispersion patterns. It also causes the speaker to lose 6dB of sound at that level (which is why you see 2.5 way speakers around - the ".5" woofer makes up for the baffle step loss). This page explains it if interested: http://www.t-linespeakers.org/tech/bafflestep/

BTW, I have an extra case of USG Sheetrock Acoustic Caulk (bought 2, needed 1). It consists of 12 big tubes of the caulk. I am willing to send that out to somebody for a small loss on my part ($60 shipped or so- I paid $60 for it retail). If anyone is interested PM me. This is such a specialized product I doubt if I put it in the sales area anyone would notice.

Take care.

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post #24 of 27 Old 05-29-2003, 05:51 PM
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Quote:
Originally posted by ArtisTech
Nice, but the equation is new dispersion angle of the wave.
If you could provide an equation that represents the new f as a function of old value and pin size then we can find some thing here.

If you consider the port of a speaker, the port should pass all wavelength of the woofer. But in reality, it passes only a certain freq based on its physical dimension as it was tuned by the designer.
Edit:
I just remembered that low frequency below 75 Hz is not directional. Another words, the dispersion angle is 360 degree.
A port on a speaker does pass all frequencies (that are not absorbed or diffused inside the cabinet), it just doesn't reinforce them all. A properly designed speaker port is basically a Helmholtz resonator tuned to a specific frequency and Q to reinforce the bass response of the speaker.

This plot shows the bass drivers on axis frequency response, the port response is in blue. The port passes freqency band similar to the one driver produces but reinforces the frequency dip in the driver's response.

http://www.cmcpics.homestead.com/portplot.gif

A hole or slot in a wall has no mass of air trapped behind it to store and release energy, so it will not resonate. You can seal off an area behind a slot or hole in the wall and create a resonator that will act as both an absorber and diffusor.

This was done a thousand years ago in the churches of Sweden and Denmark where pots or jars were embedded in the walls and partially filled with ashes to act as resonant absorbers and improve the acoustics of the space. Still practiced today. Reference: Master Handbook of Acoustics by Everest, 4th Edition, Chapter 15

What does all this have to do with caulk selection? Since the caulk will be used to block holes; and most problematic frequencies are the lowest frequencies because they travel the furthest on the other side of the hole; and to block low frequencies requires dense material, it follows that the best caulk would be the densest caulk. Acoustic caulk is highly filled with powdered limestone to increase the density. Any caulk is better than no caulk, and caulk that stays put is even better. If you are not going for true acoustic caulk, I'd suggest that you go with 100% silicone caulk for maximum performance.
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post #25 of 27 Old 05-30-2003, 06:45 AM
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Interesting stuffs. Thanks all for replying.

I need to make a clarification that I meant a small cracks only allows transmission of a upper portion of a low frequencies of 75 Hz and below. It really depends on the size of it.

This port in above graph attenuates (actually it is 180 out of phase with respect to woofer response) the 30~ 50Hz and de-attanuating any thing above. So from the stand point of this port alone, it has a single frequency response of around 42 Hz. The rest of the response cannot be heard.

A foot note:this graph is all about upper base~low mid range response not base and the woofer is a poor one in the base.

As far as the USG AQ caulk, I am actually for this product not because it blocks low frequencies. Any opening in a wall has to be sealed. Most over the counter stuffs crystallizes by time and become brittle. Assuming a wall on constant vibration, the seal will crack eventually and air will leak. Also, other sealants may not have the weight to withstand the sound pressure that is applied to the sealant. So make sure all cracks not only are sealed, but also they are filled. The USG caulks far as I read provides a longer life of plasticity properties and the weight needed to withstand the energy exerted on it by both the direct sound and enclosure vibrations. Now I wish I had the money;) .

RonAuger,

I did not know about the riser configuration. That make sense.

Thanks fellows.

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post #26 of 27 Old 05-30-2003, 06:52 AM
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Side note: USG is one of the larger drywall producers out there and their webside indicates to caulk the seams rather than mud because acoustic vibrations will cause seam failure and leak. This is less of an issue with double drwall, and unless you have a double drywalled isolated (floating) ceiling it's not even worth considering. In a situation such as a suspended ceiling. the ceiling itself is your biggest acoustic hole, rendering such caulk conversations moot IMHO.

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post #27 of 27 Old 05-30-2003, 07:51 AM
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HD here sells 10oz. tubes of siliconized rubber for $2.49. I purchased Acoustical Sealant in 29oz. tubes for $7.12. If my math is correct, that makes the true acoustical caulk less money than silicon by about .35 based upon 30oz.

As for the precautions, take a look at the MSDS sheet for most of the products you may use everyday around your home, interesting reading that'll make you never want to buy any chemical product again!
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