[Ted White]

Posted With Permission from AVS Forum



If you live in Michigan and are ready to hang drywall in your theater, please read on. I'd like to coordinate field testing of a new resonance-eliminating coating technology.


I don't want this to be a commercial, but so that you know what you're getting into, let me just say that the products remove resonance which means you have far less sound transmission through walls and sound coloration caused by resonance.


It is applied in-between layers of drywall. Applied like paint.


Interested parties will be required to apply the material themselves, take photos and notes and have acoustic measurements taken after the project is completed.


Please PM me if interested.

 

[Ted White]

Room should be using double drywall.

 

[suffolk112000]

I would be interested, but I may be some time away from starting the drywall process. My builder is behind schedule and I know it will be this fall before drywalling starts. If you have not found any takers between now and then, PM me. Tell us a little more about this product.


Since every room is different, how are you going to tell if the product truly makes a difference?

Who has to pay for the acoustic measurements?


I am probably not the best candidate because of my far off completion date, but if I know more info about what you want to do, I could let you know if this is something that would work for both of us.




Craig

 

[Ted White]

Hi Craig,


I have a couple of interested parties so far. The field testing is as much about checking the ease of application and direction following (from a customer's perspective) as it is performance measurement.


No question each room is different, but each standard wall construction has a target / estimated STC. We're looking for deviation from what would be anticipated without the product.


Those of you that know me over the years or have visited my HT website know that I have gone to sometimes embarrassing levels to achieve as much acoustic isolation as possible. By and large the results are as expected, but it became obvious to me that bass is really the nemesis. It still gets out of my room. And that's from a room within a room. I was wondering what I would do differently if I were to build another HT.


About a year ago I started discussing this with a couple of pretty bright chemists who took an interest in my situation. I've known these guys for years because we share a keen interest in the hobby of speaker design, so they certainly understood acoustics and resonance. I described to them how theater roome were built In time they created a small family of products to directly attack vibration and resonance.


Most will recall from gradeschool science class the video of the bridge being torn apart, whipped into a contorted sine-like wave. That's resonance. You're also aware that if a strong vocalist can match the resonance frequency of a glass, it can shatter. That's resonance.


My theater room and everyone else's out there can suffer from resonance as well. At certain resonance frequencies the sound is amplified and shoots through our walls as if they weren't there. This resonance will also be added back into the room as decidedly unwanted coloration. We try hard to keep the bass in the room (and not wake the kids) with a great deal of mass in the walls (drywall). We try and give the resonance a place to go with damping agents such as drywall adhesive, rubber, or mass loaded vinyl. This turns out to be a key part of our problem. These damping agents don't work very well.


The resonance in the wall is unfortunately effectively propogated because the walls are very stiff. The stiffness allows the sound vibration to collect and resonate. Some of the vibration is "released" as sound out of the room as well as back into the room. I wished that I had a perfectly damped wall, floor and ceiling system that would convert this vibration into another form of energy like heat.


In time that's exactly what my chemist friends came up with. The troweled-on vibration-defeating coatings are layered in between the drywall. On a micro level the two drywall layers "slide" against each other due to the acoustic vibration. The coatings immediately converted the vibration to heat. The damping products don't block, they diffuse.


Now this isn't a new concept. Most have heard of Dynamat. A great product if you have several thousands of dollars to spare. The world could use a product that performs significantly better at a cost almost an order of magnitude less.


Another interesting point when discussing isolation is how limited STC is. STC is an average measurement of sound containment over a broad frequency range. This measurement starts at 125hz, since that's where most "noise" starts. The problem in our HT universe is that's still above the point that my subwoofers even start kickin' in. Mine are crossed over at 90hz. Now if you were too look at a graph that took into account STC measurements BELOW 125 hz. you'd cry. Bass starts bleeding through. All of this mass didn't eliminate the resonance of the walls, it just pushes it to a lower frequency. Measure the STC down to 40hz. and you'll see the resonance problem that we all face and hear. If we HT builders want to really consider the sound containment of our rooms, then we had better take into consideration the wall performance well below 125hz.


So what I want to do is to field test these coatings with some fellow HT fans. They'll receive the great benefit of a super damped room which will significantly increase sound isolation and significantly reduce sound coloration in the theater itself. What I get is great field data. I'm contracting out the third party acoustic testing to Chris Collins.


An informational website will be up next week which describes all of this in infinite detail including all of the test data and ASTM testing protocols.

 

[BasementBob]

Ted:


I am very interested in any variations of soundproofing.


Are you going to do any laboratory testing, say at Riverbank ?


I've heard this sort of material you're proposing works great at damping steel, but isn't so good at damping drywall/gypsum. Is what you're doing similar to QuietRock? (which isn't much better, dollar for dollar, than just more gypsum and more space in a decoupled wall IMO)


Yes bass is the bane of soundproofing's existance. Eric Desart is fond of new standard called MTC (Music Transmission Class) which is slanted towards the bass rather than STC's speach frequencies.

Quote:

Now if you were too look at a graph that took into account STC measurements BELOW 125 hz. you'd cry.

I'll post some STC vs TL-frequency graphs later. But here's some numbers right now, according to PAC International's RSIC-1 RAL TL01-212 test {2 layers of 5/8, RSIC, 2x4 with 6.5" insulation, 3 layers of 5/8} they got the following TL

STC-63

31.5hz 14db TL

40hz 23db

50hz 26db

63hz 32db

80hz 38db

100hz 41db

125hz 47db

250hz 56db

500hz 60db

1khz 66db

2khz 64db

4khz 73


So, if you're playing 31.5hz sound at 100db in your HT, then in the next room it's at least 86db. I'm thinking the kids might hear that.


Have you been to http://www.mcmaster.com/ and searched for product 9545T1 ?


BTW, if you'd like to try your product on steel, I know a guy in the UK who's doing a really high soundproofed studio that has a garage door problem.

 

[ScottF200]

Quote:

Originally posted by Ted White It is applied in-between layers of drywall. Applied like paint.

Very interesting thead Ted. I would have thought it would be applied on the outside instead of being compressed between layers. Curious. I wonder if you plan any experiments where it gets put on one side of the drywall then that goes up on the 2x4s then you do the other side. Then put the 2nd sheet of drywall up. ie. have it on the outside instead of or in addition to.


Some links of things mentioned plus the Quiet stuff I see in mags all the time.

Dynamat Dynashield (spray - diff than Dynamat sheets{Dynamat is a thin, flexible, easy-to-cut-and-mold material that stops noise-causing resonance and vibration.})

Vibration Damping Compound (McMaster)

Quite Kote damping spray




P.S. My floating floor and double wall with 2 sheets of 5/8" on the inside and outside has worked out beyond my expectations. My room is different that most in many ways however (i.e. location in house and layout in houses floorplan).




P.S.S. http://www.studiotips.com/term.html
Quote:

MTC - music transmission class, a wall rating system from US gypsum

http://www.aecinfo.com/1/resourcefile/01/05/00/09264.htm
Quote:

STC/MTC: STC and MTC are ratings of a partition's sound attenuation performance. Partitions shall be tested by an independent acoustical laboratory in accordance with ASTM E 90 - Laboratory Measurement of Sound Transmission Loss of Building Partitions. STC shall be determined in accordance with ASTM E 413 - Determination of Sound Transmission Class. MTC shall be determined in accordance with criteria published by United States Gypsum Company and shall describe partition's attenuation of low-frequency noise from music, machinery, or mechanical equipment.

 

[Ted White]

Hello Bob,


Scott, how the heck are ya? I still get e-mails of your fantastic woodwork.


You can find data all over the internet that looks very similar to what Bob posted . Big acoustic holes at lower frequencies. Thanks for sharing that. Actually you Canadians have done some of the best research on this exact subject. Amazing and exhaustive research that really helped us out immensely.


On our website we propose the use of the term XSTC, which takes bass range measurements into the average.


The drywall isn't as rigid as the steel you mentioned, and therefore a surface coating alone isn't as effective. You need a constrained layer system...a drywall sandwich with the coating in between.


Scott, you can apply the coating to the stud edge then apply the drywall.


As a side note, one of the materials we have allows for a 50 to 55 XSTC wall. The wild thing is that it's a single 2x4 wall. Two layers of 5/8 on either side. A good way to go to conserve room length, width and height.

 

[BasementBob]

 A good definition of how to compute MTC can be found in a word document, from the link called "Something more about STC, MTC, OITC and RW "


STC-54

{2 layers of 1/2", staggered studs, 2 layers of 1/2", mass-air-mass 53hz}
http://www.bobgolds.com/STC54-12G2-S...150mm-12G2.JPG


STC-71

{3 layers of 5/8", double stud 340mm airgap, 2 layers of 5/8", mass-air-mass 28hz}
http://www.bobgolds.com/STC71-16G3-D...340mm-16G2.JPG

 

[Ted White]

Bob,


Your PM is full. If you could empty it, I'd send you a link or two.

 

[Dennis Erskine]

Constrained dampening systems are interesting and I'll be intrigued with the results of your testing. In the research I was involved in on such systems and materials, we had no interest in the acoustics on the sound side of the barrier. In other words, simply an isolation exercise. In such systems where diaphragmatic activity was utilized, the elastic material experiences very little compression rather there is a shearing force parallel to the barrier's surface. The problem with diaphragmatic action was (and is) in the unpredictable nature of the barrier. In quality sound applications, having the barrier behave as a speaker was not acceptable.


We found the most effective barriers were a composite of very rigid, high mass materials. Two of the constraining layers were thin, non compressible and shearing and one layer of thick (1/4", compressible material designed for little shearing forces). Among the key findings were the dampening material had to have strong adhesion to the two surfaces to be effective. When that is done, diaphragmatic action is reduced and the forces act 90 degrees to the barrier (shearing). Rigidity of the barrier can be thus maintained.

 

[BasementBob]

Ted:


Sorry about that. There should be room to PM me again.

 

[Dennis Erskine]

Quote:

So, if you're playing 31.5hz sound at 100db in your HT, then in the next room it's at least 86db. I'm thinking the kids might hear that.

Bob, you seem to like to run lots and lots of plots. Why don't you plot both of the above curves against Robinson & Dadson...so rather than showing discouraging numbers on the low frequencies, your charts would reflect how loud the sound seems to be to human hearing. IE, 86 dB SPL at 31.5Hz has the same loudness as 1kHz at 38 dB SPL (slightly above the average ambient noise floor in a residential room). [Then to avoid our thinking we hear it, we must isolate the structure so we (and the kids) don't confuse the tactile sensation with the auditory one.]


The basic and fundamental problem with STC, MTC, XTC ... or whatever curves is that those not moderately versed in acoustics get worked up over low transmission losses in the low bass region. My suggestion (Ted) is if you're going to go to the trouble of inventing YAC (Yet Another Curve) or YAM (Yet Another Metric), why not invent one that conveys meaning to the consumer...one that reflects the perceived level of loudness. That could avoid many excursions (with a consumer) down the road of Phons, logs, decibels, and pascals (or micro pascals at that).

 

[BasementBob]

Hi Dennis:

Quote:

Why don't you plot both of the above curves against Robinson & Dadson

I do that too for constant volume sources like my furnace. But to use equal loudness curves I have to know how loud the sound is on the outside of the theater, because they are not constant curves. I listen to HT at 65db, but some people would listen at 100db, and the difference will have a startling effect on the resulting phons after applying the appropriate Fletch-Munson Robinson-Dadson curve and the TL, since that curve is so variable in the bass region.

 

[Dennis Erskine]

Well, yes it is, Bob. On the other hand, if you take the leap that the TL is accurate, you could plot the curve at SMPTE reference level. That would be my suggestion to Ted as well for his "XTC" (although, Ted, I'd suggest something other than "X" to avoid confusion with the "X curve". There is also the difficulty of not having a reference distance.


....and why the temporary inactivity?

 

[BasementBob]

Dennis:

TL and DB and Loudness for an STC-71 wall with HT at 85db at all frequencies


What's the definition of the "SMPTE reference level" ?

 

[Ted White]

Dennis,


Something I learned from you a long time ago was to maintain rigid walls to avoid a diaphram. That hasn't changed at all. The action is in fact shearing exactly as you describe.

 

[Dennis Erskine]

The dynamics of what you're doing, is effective and potentially what you're developing will end up cost effective. Among the reasons elastic constrained layer products test well but fail to deliver, is in the method of attachment. Since you're developing a product, I don't want to discuss it here (email). The quiet rock type products don't meet the expectations the lab tests would suggest because of the limiting factors associated with installation requirements in real building.


How adhesive is it?

 

[Ted White]

Dennis,


The adhesion is a big factor. It's tremendously adhesive.


You had a huge part in planting this seed almost 5 years ago Dennis. Remember the inner tubes?

 

[Dennis Erskine]

The SMPTE (Society of Motion Picture and Television Engineers) has a reference level for theaters. All motion pictures (well, not all, but the vast majority of them) are mixed on the standard reference theater which is calibrated to the reference level. The reason for the reference level is that when played back the theater can reproduce the same loudness throughout the spectrum as was heard by the mix engineers. 83dB SPL

 

[BasementBob]

Dennis:


I read somewhere in the past hour or so that SMPTE Reference was 83dB(C), so I'd have to find a list of C weightings to fiddle with that 83 for the various frequencies.


Bob