Mass loading...

I was perusing the Wyle report (WR 73-5R), and something bothered me. He recommends using 2 or 3 sheets of asphalt roofing paper to add extra mass. I must say I've seen a studio construction recently that also seems to have used some kind of tar-paper or roofong felt (Alan Parsons Art & Science of Sound Recording, Studio Acoustics section). The use of this material seems to be shunned on this site. Is there any reason it is no longer recommended?

The BBC uses it here http://downloads.bbc.co.uk/rd/pubs/reports/1971-15.pdf Phillip Newell says that the BBC stopped using it because of lack of consistency. He uses what he calls dead sheet, but he has compared it to roofing felt. I plan on using roofing felt in my design as part of a broadband absorber. I'm not too worried about inconsistency. :mrgreen:

Two reasons why it is frowned upon. For the money spent on 15 or 30 pound felt, with petroleum products pricing going thru the roof, it costs more per wall than it would cost for simply adding typical mass, that is sheetrock. Back in the day, when a roll of tar paper was 4.25 per 400 square feet, it may have been seen as a value, but not so much these days. The second and more important of the two, is that it is a fire hazard. In a room that is already heated and has much electricity in the walls, you want to keep your attention to the walls ability to burn at a slower rate, rather than add something, like a petroleum based product, which rapidly increases and subsequently decreases, the walls ability to burn at a slower rate. Heaven forbid ;)

The second reason is definitely the more sobering of the reasons. The first is of course a decision, what is the more valuable. Cost or space. The roofing felt adds mass with minimal thickness. But now I understand. When I was a child I remember playing with sheets of 1/8" lead - what I wouldn't give for that now...

Another thought came to me when reading that report. He mentions the use of sand, and how the major obstacle with sand is keeping it in place. To which he used something akin I suppose to the large chambered bubble wrap but filled with sand instead of air. Regardless, I thought, what if one separated two sheets of gyproc or mdf with a 1.5 or 2" sealed perimeter frame, thus making a hollow chamber (could even be compartmentalized), and flled the hollow with kiln dried sand. Might even be an alternative to a super door. Any thoughts?

what if one separated two sheets of gyproc or mdf with a 1.5 or 2" sealed perimeter frame, thus making a hollow chamber (could even be compartmentalized), and flled the hollow with kiln dried sand.

Sand is a bit like water: it acts more like a liquid than a solid, and it flows. So all of the weight of that sand will be concentrated at the bottom of the chamber, trying to force the drywall out sideways. There'll be a lot of pressure down there. Sand is almost twice as dense as water (about 1,800 kg/m3), so the "sand pressure" at the bottom of a 10 foot wall would be roughly the same as that caused by a column of water about 18 feet high. Ever noticed the pressure in your ears if you dive to the bottom of even a six foot deep swimming pool? Multiply that by three... The drywall probably won't be able to handle that for very long. It will bulge, balloon, and eventually something will fail. Even if it doesn't fail, a tiny hole or crack will have sand leaking out all over your studio... The only places I'd consider using sand in a studio, is under the floor, inside cavity bricks, and in tightly sealed sturdy speaker stands. But I don't see it as being a good idea in walls and doors. Acoustically, it would work fine for mass, but from the point of view of practical reality, and how you keep it contained, that's what worries me... Maybe I'm wrong, but it just doesn't seem like a good idea. - Stuart -

I was thinking about that problem which is why I mentioned compartmentalizing i.e. instead of a single, huge chamber, divide it up into smaller compartments.

BriHar wrote:

The first is of course a decision, what is the more valuable. Cost or space. The roofing felt adds mass with minimal thickness.

No sir it does not add mass like you are thinking. If space is pertinent..then use lead sheets :) The inconstancyof sheetrock is one thing, the inconstancy of a paper covered in asphalt, surely another thing. Let us design a room without sheetrock...put tarpaper up on all the walls...what do you thing you would get in the Tl? Let us dismiss the TL,,,what about the penetrations.....? If the wall assembly has to have 30 pound felt as part of the barrier, a part that has not been tested, then why not throw some other generic supposed mass loaded material, at the assembly?

This is from Auralex about their product Sheetblok which is designed as the replacement where roofing felt was used in the past.

SheetBlok™ Professional Sound Barrier Auralex’s proprietary limp mass, dense vinyl sound barrier material available in 10’x4’ sections or 30’x4’ rolls. It is 1# per square foot, 1/8” thick, highly flame retardant, easy to install with plastic-cap nails, staples or trowel-applied PL PRO construction adhesive or multipurpose floor adhesive and yields a great Sound Transmission Class (STC) of 27. Compared with a sheet of solid lead which only yields an STC of about 21, SheetBlok is safer, cheaper, easier to work with, more effective, easy to cut with scissors or an ordinary utility knife and UPS shippable (when necessary) right to your door. It is used to “float” walls, floors & ceilings (isolate them from the rest of the structure), or as one or more of the layers in a wall or ceiling intended to block the transmission of sound to neighboring spaces. It has been used with great success by our most famous clients & is simply unbeatable. SheetBlok is quite simply one of the best investments in good sound control that you’ll ever make

They claim an STC reduction of 6dB over lead sheeting.

They claim an STC reduction of 6dB over lead sheeting.

I bet I can do better than both with something like, umm, drywall, maybe? :) Quite a bit cheaper, too. I always see red flags waving wildly when claims come up about magical products with apparently magical properties. Some manufacturers in the magic industry do indeed like to "prove" how magical they are, by comparing their magic tricks against an undefined "something", that sounds like it should do so much better, but since they never actually DEFINE what they are comparing against, it all turns out to be meaningless hype, as soon as you look under the hood. So what did they compare against here? "a sheet of solid lead which only yields an STC of about 21". Ummm.... question: How thick was that lead sheet? Seems rather strange that this minor little detail wasn't mentioned. I wonder why they didn't mention that? Was it one micron thick or one inch thick? Hmmmm.... I'm betting that a sheet of lead the same thickness as this MLV would come out ahead on any acoustic isolation test for STC that you can think of. I'm betting that the "sheet of solid lead which only yields an STC of about 21" was somewhat thinner and with a somewhat lower surface density than the MLV. Why would I bet on that? Because you can't beat the laws of physics with marketing hype, that's why! Physics will win, every time. Since a single sheet of MLV must obey mass law at STC frequencies, and so must a single sheet of lead sheeting, there is no contest. A piece of MLV that is, for example, 4mm thick will NOT outperform a piece of lead sheeting that is also 4mm thick. Neither will 6 mm thick MLV outperform 6 mm lead sheeting. Ain't gonna happen. Or rather, it wont happen if you test both products correctly in a reputable, independent, acoustical laboratory. (Of course, it might well happen if you test both materials in the unknown lab of some or other manufacturer! What a surprise! Under those circumstances, I'm sure that 1 mm MLV can outperform even 6 inches of lead! Not the slightest doubt... ) And of course, roofing felt is not MLV anyway, so I'm not sure where that comparison is even going: I thought the discussion was about roofing felt?

That is why I phrased it "they claim." But, Phillip Newell is a big proponent of a product like this. He calls it deadsheet. He says it is an updated version of roofing felt (which is inconsistent in its mass) but is used in the same way. If I remember the theory correctly, the limp mass deadens vibrations as well as adding mass to the wall. It can also be used effectively as a membrane absorber.

If I remember the theory correctly, the limp mass deadens vibrations as well as adding mass to the wall.

If you compare the results of adding an extra sheet of 5/8" drywall or adding a layer of MLV instead, the drywall will beat the MLV, every time, and for a somewhat lower cost. Mass is mass. The sound waves really don't care how much you pay for the mass: all they do is react to the mass. Sure, limp mass has rather different resonant characteristics than rigid mass, but that isn't much of an issue at STC frequencies, which is what MLV manufacturers always seem to want to quote. Rarely do you see an MLV manufacturer talking about how good his product is for overall TL, and even more rarely do you see actual independent tests of such products up against real-world alternatives, such as for example an extra layer of 5/8 drywall, or Green Glue, for example. Maybe its a semantics thing, but I'm not sure how you would use MLV to make a membrane trap, since membrane traps are tuned and rely on the resonance of the membrane plus the air depth behind it, but MLV has no resonance... I'm sure you can build some kind of effective trap with it, but I'm not sure that the term "membrane trap" would be technically applicable. I'd also like to see the data that shows how MLV is acoustically the same as roofing felt. That sounds rather questionable, to say the least. - Stuart -

OK, back to the roofing-felt, So why are many studios still being constructed using this stuff? I mentioned the Keyfax studio from ASSR, plus this info from Northward (who seems to know what he's talkiing about) on Gearslutz http://www.gearslutz.com/board/studio-building-acoustics/579437-roll-roofing.html#post6311219 also, http://www.gearslutz.com/board/photo-diaries-recording-studio-construction-projects/304215-amsterdam-mastering-construction-thread-3.html#post3499007

So why are many studios still being constructed using this stuff?

Good question! I guess the exact same question could be asked about why so many home studios have egg crates on the ceiling and carpet on the walls... :) (There sure do seem to be a lot of those around...) Anyway, personally I'm not too interested in becoming a guinea pig for some technique or other that lots of people are using (even if some do seem to know what they are talking about), unless, firstly, there is ample data from real acoustic tests to support the notion that it will work, secondly there is no other method that will achieve the same ends better/cheaper/easier, and thirdly that using it doesn't introduce unnecessary risks, such as fire hazards, for example. The way I see it, my goal is to build a studio that works well acoustically at the lowest practical cost. My goal is not to build an acoustic test laboratory and try out things that may or may not work, especially when they are more expensive than proven methods that accomplish the same thing, safely. But that's just my personal philosophy: others may disagree. If somebody wants to be adventurous, and is prepared to live with the unknown consequences of these techniques, if they have time and money to waste, and like being there very own acoustic laboratory, then who am I to question that? - Stuart -

"But, Phillip Newell is a big proponent of a product like this." In what year are we talking? Not to dismiss Mr. Newell, he is head and shoulders over me, but still...what he does is not what we do. He does not teach nor present data that can be replicated. What he does is build things based on a lot of math...BIG projects...way out of our league and price range...and for me, hard to replicate in a home recording environment.

Actually one of Newel's early books is about smaller studios in 2001. It is an adaptation of his and Hidley's "Non-Environment" rooms that they developed in the '90. http://www.amazon.com/Project-Studios-more-professional-approach/dp/0240515730 This book was originally released in 2006 with a new edition in 2011. He goes through just about every type of studio design here. http://www.amazon.com/Recording-Studio-Design-Philip-Newell/dp/0240522400/ref=sr_1_4?s=books&ie=UTF8&qid=1315539347&sr=1-4 more books http://www.amazon.com/Loudspeakers-recording-reproduction-Philip-Newell/dp/0240520149/ref=sr_1_8?s=books&ie=UTF8&qid=1315539508&sr=1-8 http://www.amazon.com/Recording-Spaces-PHILIP-NEWELL/dp/0240516273/ref=sr_1_18?s=books&ie=UTF8&qid=1315539633&sr=1-18 http://www.amazon.com/Studio-Monitoring-Design-PHILIP-NEWELL/dp/0240514076/ref=sr_1_27?s=books&ie=UTF8&qid=1315539690&sr=1-27 His acoustic ideas are not limited and I think he is a very good teacher. Sometimes he does throw in some math, but nothing very high end. Behaviors can be predicted mathematically. Building a studio is about mathematics (of course I say that because my degree is in Mathematics) no matter what the scale. I have treated a couple of rooms based solely on the mathematics (and a couple of performance venues). I wrote a spreadsheet based on the equations form Everest's MHofA to get a balance rt60 and treat the modes 20+ years ago. These rooms turned out very balanced and are still in use. (not the performance venues though). I wonder why I don't hear much talk around here balancing the reverb time in rooms anymore. There are some very good spreadsheets written to do this (much better than my old one).

The only places that I can find testing data on Mass Loaded Vinyl is on the green glue site. Where the compare their product to the Auralex product. The part I find interesting is that they compare a wall with two layers of drywall on each side with green glue in between to a wall with a single sheet of drywall one and a double layer with MLV on the other. They also have no consistency with the drywall thickness and their comparisons. Some of the walls use 1/2 inch, other use 5/8. Like walls are not compared to each other. http://www.greengluecompany.com/greenGlue-vs-MLV.php

See also on the same link above, the section further down: Appendix – discussion of damping, limp mass, and how they operate.

The only places that I can find testing data on Mass Loaded Vinyl is on the green glue site.

Exactly :!: : Thank you for making my point! :) there simply isn't much published information on it, and what little there is spotty and incomplete! Yet, DESPITE this rather glaring lack of solid reliable testing, here we have all these manufacturers, all over the place, making wild and magical claims against the character and nature of MLV. Your honor, I rest my case: The accused, "Mr. MLV", is clearly innocent of all charges of having any use in acoustic isolation, due to the total lack of evidence in support of the unfounded accusations brought against him, claiming that he is, in fact, guilty of being a useful member of the family of acoustical products... :) - Stuart -

We started this topic on felt...we should stay there... Mass Loaded vinyl, look it up, it is a construction curtain. It does what it is supposed to do in that context, but it cost money and the balance of mass versus cash makes it not worth the effort. Felt...I do not care who presents it, Phillip Newell included, is a poor choice of material, per cost, per consistancy, etc. etc. That said...use it at your own risk :)

Brien, Phillip Newell doesn't use roofing felt anywhere, but uses plastic limp mass which he calls "deadsheet" almost everywhere. He was the one who I took the statement about the BBC using it at one time but discontinued because of lack of consistency. From his book Recording Studio Design

4.5.6 Membrane absorbers These consist of a flexible, impervious sheet in place of the panel material shown in Figure 4.27. If the sheet is sufficiently ‘lossy’, and has a low bending stiffness, very significant amounts of acoustic energy can be turned into heat within the material of the sheet membrane. The air behind provides a damping spring. The membranes are typically plasticised bituminous material or mineral loaded flexible plastics. Polymer materials of high internal loss are also used. The early work on these absorbers was done by the BBC using bituminous roofing felt as the membrane. The trials were dogged by the tendency of the characteristics of the materials to change with temperature and time, and they were also inconsistent from batch to batch, even from the same manufacturer. Specially produced materials are now in widespread use around the world, and many specialist acoustic material manufacturers have their own proprietary types. Dependent on use, such ‘deadsheets’ as they are commonly known, range in weight from around 3 to 15 kg/m2. The lower weights are used more for acoustic control, whilst the higher weights are more effective for sound isolation. These materials will be considered further in later chapters. What these deadsheets have in common is that they are all very highly damped.

I think your observation about fire is a good enough reason not to use roofing felt whether it works or not.

The idea, as Mr. Newell presents it, is to damp the panels, right? Which is a common thing, or used to be, among diy speaker enclosure makers, that 30 pound felt was used in an attempt to construct a constrained layer damped cabinet. I think we all recognize this is more a dry friction effect, with no real cld effect.