Homasote Test

I contacted Homasote requesting absorption test data and received the attached report. Interestingly a membrane effect is quite apparent. Looking at the absorption data I would not recommend this for any amateur design application. Andre

Thanks for going above and beyond as usual Andre! Greg

That's very interesting! Thanks, Andre! Great find. Any idea what they mean by the sample being a "perforated plug"? In what way was it "perforated"? Is that something to do with the test procedure, or did it have holes in it? It would be great if they would repeat that test for a broader range of frequencies. There's some interesting hints in there, but more data would be nice. I'm intrigued... - Stuart -

Soundman2020 wrote:

That's very interesting! Thanks, Andre! Great find.

You are welcome, as always.

Any idea what they mean by the sample being a "perforated plug"? In what way was it "perforated"? Is that something to do with the test procedure, or did it have holes in it?

It does not help your using the pronoun. The report is from the testing laboratory. The perforations are an integral part of the test specimen.

It would be great if they would repeat that test for a broader range of frequencies. There's some interesting hints in there, but more data would be nice.

An important clue to the importance Homasote corporation makes of it being an acoustic absorbent is that the test report is from 1967. The frequencies tested are what is required for NRC calculation. Andre

I received a copy of a test to C423. Enjoy! Andre

Cool! I have NO idea how you come up with all this stuff, Andre, but it's great! You seem to have a magic hat, that you can just pull this stuff out of any time it is needed... :) There's very interesting data in that lab report. Absorption peak around 125 Hz... Hmmmmm.... It's not a huge peak, at 0.55, but useful.... and suggestive! Thanks, Andre! - Stuart -

Andre The Librarian..... or Oracle? Thanks Andre. I have noted that some commercial batt traps have quite a ring to them when thumped. As I am a drummer I have a Tunebot, which measures the frequency of impulsive tones. I must try a RealTrap and a GIK outdoors, soon, as the weather is getting good here. DD

Greetings from the Homasote Tech Desk!

AVare wrote:

An important clue to the importance Homasote corporation makes of it being an acoustic absorbent is that the test report is from 1967.

Andre is correct in that acoustical improvement has never been the primary focus of Homasote, even though our very first sound test, done in 1931, was for NRC. Here is that test, if any of you is interested in a little history. In fact after the 1967 sound test we received a letter basically saying that Homasote would never be a good acoustical panel. here's that letter. The problem with all that is I hear a great deal of anecdotal evidence that the Homasote substrate does indeed provide an interesting degree of acoustical improvement. It could be that 125 Hz bump for starters. When I installed a number of raw Homasote panels in my small singer/songwriter studio it noticeably improved the sound of my vocals and particularly my acoustic guitar recordings. You know how small rooms can be in that general frequency range. But I also speculate that there is a good degree of scattering going on due to the unique nature of the boards surface. There are some very interesting surface anomalies that come from the manufacturing process. I would be curious about how you folks perceived that possibility. I have done some research on testing for Scattering Coefficient but many acoustical folks seem a bit skeptical of that. For what it's worth, Homasote 440 SoundBarrier plays heavily in the multi-family sound control market where it is a great sub for poured gypsum on floors and does pretty much what Green Glue does on walls. But then that would be a different discussion and that's not what I'm here for. Now that I am here, I intend to hang around a bit and see what I can learn from folks like Andre Vare who know a whole lot more about all this than I do

Hi there "sgleaosn". Thanks for that very interesting information, adding to what Andre already found. It would be good if you could introduce yourself, since you seem to be speaking the Homasote Company, which would be great, since your product is used by many of our members: having a direct connection would be useful, especially for those members in various places around the world who have tried to find your product in their countries, without success. Most members who use your product, want it to make bass trap "hangers" for their studios, since that's what John Sayers himself recommends and has used extensively in his own designs, as have numerous forum members. It does seem to be the best material for that, although some people have used other materials successfully too. So please read the forum rules for posting (click here). You seem to be missing a couple of things! :) Hopefully Andre will reply to your comments about the acoustic properties you mentioned. - Stuart -

Sgleaosn: Welcome to John L Sayrt's Recording Stdio Design (JLS RSD). I am glad you decided to join in. The information that you provided is great!! I am not certain what Soundman2020 is looking for further discussion. Hopefully he will expand on that' In the mean time, enjoy! Andre

Hey Stuart...........I have taken care of a bit of housekeeping on my profile. While I will be pleased to help anyone interested in the Homasote product, I will be spending my time here learning. Thanks for the welcome, Andre. Steve

SGleason wrote:

While I will be pleased to help anyone interested in the Homasote product, I will be spending my time here learning. Thanks for the welcome, Andre.

Welcome to JLS RSD and you are welcome. Regarding information on Homasote in sound isolation applications, in studio apllications the sub 125 Hz TL is important Fortunately our bible of gypsum board sound isolation (IR 761) has TL data down to 50 Hz for over 350 wall assemblies. Only two use any material resembling Homasote and from I can glean it is probably Sonopan. You can read how it (and resilent channel) compre to regular walls here http://johnlsayers.com/phpBB2/viewtopic.php?f=2&t=1499&hilit=below+100Hz Do you have any TL test data below 125 Hz for Homasote walls that you can share with us? Sorry about the wordiness but if can share it please do. Andre

Sonopan is a very different substrate than Homasote. The best we have for low frequency TL data is 100 Hz and 125 Hz. For what it's worth: Single Wood Stud (FG Insulation) - 27 dB @100 Hz, 28 dB @125 Hz Single Wood Stud (MW Insulation) - 25 dB @100 Hz, 29 dB @125 Hz 5/8" Type C GWB both sides Homasote 440 SoundBarrier (source side only) Single 25 ga. Metal Stud (FG Insulation) - 30 dB @100 Hz, 36 dB @125 Hz Single 25 ga. Metal Stud (MW Insulation) - 27 dB @100 Hz, 34 dB @125 Hz 5/8" Type X GWB both sides Homasote 440 SoundBarrier (source side only) Drywall screwed only to Homasote in the field of the wall Adhesive beads between GWB and 440 in stud bays Steve

Thank you Steve! The 100 Hz TL is 5 to 8 dB better than the walls with the fibre board in IR 761. The results are on pdf pages 252 and 253. The question is how the MAM resonance is affected. Andre

Thanks for that reference to IR 761. I have that in front of me often. In TL-93-192 they tested with fiber board on both sides of the wall and (2x) GWB on one side (STC 50). While they do not go into the fastening protocols, it's a very good bet that the GWB was fastened through that fiber board and into the studs. With the Homasote wall, Homasote is on the source side only and the GWB is fastened only to the Homasote in the field of the wall. I believe that makes a measurable improvement in a wood stud assembly but maybe not so much withe steel studs. I am unclear as to where in the frequency range that improvement is most manifest. That wall tested at STC 53 with (1x) GWB on both sides. Here is the test (redacted for file size): Regarding MAM resonance, When the company tested a single wood stud wall some years ago they found that the assembly performed better with the Homasote on just one side. I theorize that the cavity resonance becomes "asymmetrical", if you will, when there is an imbalance like that (GWB facing Homasote). I do not know how to quantify that but it looks to be improving the performance of the assembly at the low end.....possibly making the cavity perform as if it was deeper. Love to hear your comments on that. EDIT: Just reading in NRC 4068 where Bradley references the "stiffness of the contained air".....definitely pondering that. Steve

Thank you Steve and great stuff! Andre

Just reading in NRC 4068 where Bradley references the "stiffness of the contained air".....definitely pondering that.

Hi Steve. I would guess that refers to the amount of damping in the void. I have some Isover test data here which shows maximum benefit with a full fill. It also shows no difference in performance over a very wide range of densities. I usually recommend such, with the fibre actually touching both leaves. I am assuming a light touch there will dampen bending resonances. I have never seen any test or even theory confirming this, nor any attempt to suggest how much touching. We know of course that fibre stuffed in there will cause LF transmission. So for now for me, full fill, lightly touching. Many seem to miss the Isover point that a full fill is best, and that even a small airgap in there is unhelpful. Indeed a so called Professional Consultant here insisted to me that loose batts in there are best, to avoid touching. Thoughts? DD

Many seem to miss the Isover point that a full fill is best, and that even a small airgap in there is unhelpful.

Very true! I have no idea why people would not want to fill the cavity entirely. It's just logical, and also supported by research.

Indeed a so called Professional Consultant here insisted to me that loose batts in there are best, to avoid touching.

Strange advice indeed... - Stuart -

DanDan wrote:

We know of course that fibre stuffed in there will cause LF transmission. So for now for me, full fill, lightly touching.

Hey DanDan..... I definitely think that a firm fill with a light touch in a wall cavity is the best way to go. Occasionally someone will ask me about stuffing 6" of fluffy in a 4" cavity and I advise against it, of course, as I believe that those compressed fibers can become a physical transmission path at that point. I do have to wonder, though, if that light touch is enough to damp the resonance of the plane.

no difference in performance over a very wide range of densities.

In the data that I posted early you can see an overall STC 1 difference between mineral wool and fiberglass. We deal a lot with floor/ceiling assemblies where it may be a different dynamic. It has been suggested that with a 12" cavity half filled with pink fluffy there could be a subtle impedance mismatch that is created between the air and the insulation that causes some shear. It'll be tough to get any real data to back that up, though. Steve

SGleason wrote:

In the data that I posted early you can see an overall STC 1 difference between mineral wool and fiberglass.

Incomplete reporting confuses issues. People misconstrue IR-761 data as showing that glass fibre is better. What it does show is that insulation that is 2 to 8 times denser is not as good. See fig 2 on pdf page 17 for insulation densities. We have known for decades that lighter is better for filling cavities. Andre

We deal a lot with floor/ceiling assemblies where it may be a different dynamic. It has been suggested that with a 12" cavity half filled with pink fluffy there could be a subtle impedance mismatch that is created between the air and the insulation that causes some shear. It'll be tough to get any real data to back that up, though.

As you say, I'd like to see the data that shows such an effect! :) Many people have the wrong idea about what insulation in the cavity does: some people think it just "stops sound" from getting through. That's not really true. If you took the same thickness of insulation and placed it directly in front of a speaker playing typical contemporary music, you'd hear the music fairly well. Muffled highs, yes, and muddy mids, it is true, but you'd still hear it with just a small reduction. Only slight TL drop like that. Insulation by itself is pretty bad at "stopping the flow of sound" on its own. But what it DOES do very well, is to damp resonance. I often use the analogy of a kitchen sponge: If you spilled some water in your kitchen, and need to mop it up, then a sponge is a good way of doing that: it picks up the water very well, then you can squeeze out the water in the sink (or wait for the sponge to dry), and mop up more spills. You can carry on mopping up and squeezing out all day, with no problem! Sponges are good at that. But if you then turn on the tap and hold the sponge over the end of it, the water comes pouring through, as though the sponge wasn't even there. It does nothing to "stop the flow". That's sort of like trying to use porous insulation to "stop the flow" of sound: it does nothing much useful. But when you make it part of a SYSTEM, then it does what it is really good at: mopping up resonance, or "damping". Inside an empty wall cavity, there are multiple resonances going on at different frequencies. There's the MSM resonance, of course, between the two sides of the wall, plus probably some modal resonances at very different frequencies, plus several others. Insulation can damp all of those, very effectively. The insulation does several things at once to help with that. Firstly, it slows down the speed of sound: sound waves travel quite a bit slower through insulation than they do through empty air, so from one point of view, the sound "sees" a longer distance between the leaves than is really there (it takes a longer time than it would have to cross the gap), secondly the presence of the insulation changes the way the air deals with heat from adiabatic to isothermal, and third, it provides impedance for the movement of sound, which isn't the same as "stopping the flow" of sound. All of those are "good things" for damping. Now, think about your 12" cavity: if you fill it only 6" deep, then you only have half the cavity with all those "good things" happening in it. The other half is just empty air, where the resonances are all still happening... and robbing the wall of isolation. Filling the cavity entirely means that the above "good things" are happening in 100% of the cavity, not just 50% of it. Filling the cavity complete with SUITABLE insulation, is actually one of the best things you can do to a wall, to increase TL. If my words don't convince you, then maybe actual data will... :) I also know that I have a report somewhere titled "The Acoustic Role Of Glass Wool In Double-Leaf Walls" someplace, but I can't find it right now. I'll dig some more, and see if it turns up... All I have is this extract: - Stuart -

Yup. There are points worth exploring though IMO. Bending waves and their resultant dip in TL at resonance. How much pressure of fibre to damp those but not decrease LF TL. DD

I can't tell you guys how much I appreciate this discussion!

Soundman2020 wrote:

I also know that I have a report somewhere titled "The Acoustic Role Of Glass Wool In Double-Leaf Walls" someplace, but I can't find it right now. I'll dig some more, and see if it turns up...

I'd love to see that report if you can find it. I appreciate your above post.

DanDan wrote:

Yup. There are points worth exploring though IMO.

Indeed. Theory is part of the learning process but it only becomes a productive exercise when it gets backed up (or not :| ) by data, right? EDIT: Would any of you like to speak of the specific relationship between RC and insulation? It is my understanding that the benefit of insulation is maximized when it is deployed in conjunction with resilient channel. I am curious about those dynamics.

SGleason wrote:

EDIT: Would any of you like to speak of the specific relationship between RC and insulation? It is my understanding that the benefit of insulation is maximized when it is deployed in conjunction with resilient channel. I am curious about those dynamics.

There is no maximizing. Insulation absorbs sound that travels through the cavity. Resilient channel was created to give acoustic isolation to wood stud walls as metal studs. Below the STC frequencies it is actually worse. It works reducing the strength of the mechanical connection between the leafs. Used on both leafs it makes things worse. On a double stud wall I makes TL worse. Designers have frustrations using RC because installers either miss the channel, screw into the studs and/or install the channel upside down. Andre

I'm gonna pull an Andre trick here: Take a look at the paper "NRCC-44692 : A Simple model of the sound insulation of gypsum board on resilient supports" Recently uploaded to the reference area... viewtopic.php?f=3&t=21894&p=149463 It's the last one at the bottom of the list... As you can see, and as Andre already said: RC isn't very exciting, even when tested under perfect lab conditions... Put it in the hands of a typical careless framer or drywaller, and all bets are off... - Stuart -