John Sayers' Recording Studio Design Forum Archive

How effective is the inside-out wall if only constructed as the only wall structure for the room? I've began construction of a drum room in the corner of my unfinished basement, and I was hoping to only use one set of walls. The room is about 6' wide by 10' long, so it's not very big.

My current plan is the standard inside-out wall, isolated from the rest of the structure, with three layers of drywall on for the ceiling portion (double for the rest) and GG in between the layers. I've got a solid-core door that i'm going to beef up with two layers of some sort of wood. This should be somewhat effective, correct? I know a double wall would be ideal but i'm constrained for space.

constructed as the only wall structure for the room? I've began construction of a drum room in the corner of my unfinished basement,

If you are building it "in the corner of the basement", then it isn't the only wall, is it?! You already HAVE a wall there: the basement wall. So putting ANOTHER wall in front if that means that now have TWO walls. Or more correctly, you have a two-leaf wall, where the original basement wall is the outer leaf, and they new inside-out wall is the inner leaf.

Since you are building this in a "corner" of your basement, this situation is going to happen for two sides of your drum room: the two sides that are facing the walls that meet in that corner. Now you only need to add extra walls for the other two sides, to complete the room.

My current plan is the standard inside-out wall, isolated from the rest of the structure, with three layers of drywall on for the ceiling portion (double for the rest) and GG in between the layers.

As long as you do that for all four walls, then you should get good isolation. But that's just the inner-leaf: you also need to complete the outer leaf. As I mentioned above, you already have two sides of the outer-leaf in place: you just need to add the other two sides, then build your inner-leaf as you described: four walls with a ceiling on top.

- Stuart -

Thank you for your response. I've started construction, and instead of Green Glue between layers, I used what is mentioned in this video: https://youtu.be/UtxduYYXoVY?t=360

Roberts carpet adhesive 3095 - the gentleman in the video says a world reknown studio designer recommended this, as it has similar properties to GG. It never dries, remains tacky, and he says that the results have really surprised him. You may laugh at me, and I think it's a bit silly as well, but ultimately I will see how it works when building is complete.

Roflcopterrr wrote:Thank you for your response. I've started construction, and instead of Green Glue between layers, I used what is mentioned in this video: https://youtu.be/UtxduYYXoVY?t=360

Sorry if this seems a bit harsh, but that was not a smart move at all. The statement made in the second paragraph of that video introduction shows that the author has no clue at all about the subject matter: "Acoustical glue is an important part of recording studio construction". Wrong. No it is NOT an important part of studio construction, because there's no such thing! Ignorant people make this major mistake all the time, due to the misleading name, but "Green Glue" is not glue! It is not an adhesive. It is not used to stick thinks together. That is not the purpose at all. That sentence alone disqualifies the maker of that video from offering sound advice, since the basic claim is just plain wrong. (I really wish that the Green Glue Company would have come up with a different name for their product! I have to deal with this all the time, simply because they put the word "glue" in there)

In the opening phrase he makes the very same mistake, again, saying that he has been trying to figure out what to do about the: "glue that goes between your layers of drywall"! You do NOT glue drywall layers together!!!! That is NOT what Green Glue does! He then says he could not justify spending as much money "on the glue" as on the drywall. If he truly had spoken to people who do know how to build studios, then he would know that it is not glue, and the cost is totally justified, because it is not glue! It is an ACOUSTIC product, not an adhesive product. It is used to greatly improve the acoustic isolation properties of the wall, not to glue the layers of drywall together, which is unsafe and likely illegal as well. It achieves much higher isolation, especially in certain problematic frequency ranges, and that is why people happily spend the money to buy it. Because it is the ONLY product that does the job so well, of damping acoustic issues. They don't buy it to "glue the drywall together": they buy it to isolate their rooms. So the entire video is based on a false premise: that you need to glue drywall together. Wrong.

At least he admits that his "test method" was "very very shoddy". Can't argue with that!

To show his lack of understanding even more, he even tried one test with acoustic caulk! Go figure!!!! Who in their right mind would even suspect that acoustic caulk could be used as a CLD between layers of drywall!!!?!?!? Hooooo boy!

And it turns out that in the end he did NOT use the carpet glue! What he DID use was a different CLD: they used Quiet Glue Pro, which is a direct competitor of Green Glue. He only used carpet glue right at the end, for "rooms where it did not matter".

It gets a bit hilarious later when he starts testing to see how well each of the products work "as an adhesive" then rejects Green Glue because it does not work well as an adhesive! I mean, seriously? Did he really expect an acoustic CLD compound to work as an adhesive???? This clearly demonstrate that he does not understand WHY he even used anything between the layers of drywall! He has no understanding of what he did, or why he did it, yet he thinks he can be a judge of which product worked better?

The interesting thing is that in his "tap the samples with a hammer" test, the Green Glue is very clearly vastly superior, just from the sound of it. Even though the test isn't really valid, and does not in any way examine what the product is supposed to do and designed for, it still beats out all the others, hands down. Green Glue makes no claims about impact noise, yet even with the lousy quality sound in that video, the Green Glue sample sounds very, very superior to any of the others.

Even more interesting is his final conclusion: "I wish I would have bought a whole bunch more of [the Green Glue] ... it is, in my experience, the best". However, he then goes on to try to justify making a bad decision, saying that he though that the carpet glue was "close enough"... Well, refer to my signature to see how I feel about "good enough"....

Then he second-guesses his own second-guess, and says "However, I probably really should have rather gone with all Green Glue".... In other words, he realizes that he made a huge mistake, and is now very sorry that he made a mess of his studio. He admits that it was a huge error to NOT use Green Glue, and that he really should have paid the little extra and done it right!

the gentleman in the video says a world reknown studio designer recommended this,

... and yet the "reknown studio designer" did not want to be identified, and remains nameless! I wonder why....

as it has similar properties to GG.

No it does not. Not even close, as you can hear from the "hammer test". To start with, as I already mentioned "Green Glue" is not even glue! That carpet glue is a latex adhesive, while Green Glue It is a visco-elastic polymer constrained layer damping compound ("CLD"). Nowhere near the same. Green Glue works in a very specific manner to damp certain types of resonance in the drywall itself. It does NOT stick the layers of drywall together! In fact, it keeps them apart! That's the reason why it must be applied in the manner the manufacturer states. It damps the bending waves in the drywall. Carpet glue dos NOT do that! It just doesn't. There is no published data, no laboratory test results, no theory, no papers, no studies... nothing! Green Glue is very well documented, with abundant tests in INDEPENDENT and reputable acoustic testing laboratories, with openly published results that back up the advertising claims. It works exactly as claimed. There's NOTHING AT ALL regarding carpet glue, and as the video maker himself says, the carpet glue is much "firmer" and stickier than Green Glue: therefore it is NOT the same. Not even comparable.

but ultimately I will see how it works when building is complete.

And when it does not work, will you then pull it down and re-build it the right way, using the right product?

To be very honest: If you are not gong to use Green Glue, then don't use anything! With three layers of 5/8 drywall on each leaf, you are going to get very good isolation anyway. Yes, Green Glue would make it even better and by using Green Glue properly you could probably even reduce your three layers of drywall to just two layers of drywall, but instead of using a totally inappropriate product with zero supporting test data, for a purpose that it was never designed for, just to save a few bucks, is not a good idea. Either use the right product, or don't use anything.

- Stuart -

Wow, there’s a truth bomb if I ever saw one. At least now others will be able to refer to your response if and when they consider using the product like I did.

Not that this means they are actually similar in any way, but I have seen green glue in buckets, and the carpet adhesive seems to look and behave quite similarly in terms of texture and viscosity(in their unused state.) Surely you can at least say that GG does exhibit some adhesive properties, no? I will still keep an open mind.

Not that this means they are actually similar in any way, but I have seen green glue in buckets, and the carpet adhesive seems to look and behave quite similarly in terms of texture and viscosity(in their unused state.) Surely you can at least say that GG does exhibit some adhesive properties, no? I will still keep an open mind.

Yes it DOES exhibit some adhesive properties! That's not in question. But so does a broken egg... Drop an egg on the floor, wait until it gets a bit tacky, then put a piece of drywall on top... wait a week or so until it is all set up hard, then try to lift the drywall... Not trying to be facetious: just pointing out that many things exhibit adhesive properties but that's not what they are meant for. I really really REALLY wish that the Green Glue Company would have invented a better name for their product. Call it Green Goop or Green Gunk or something like that, so it can't be confused with glue, since that is not what it does. It happens to have some stickiness, as you mentioned, but it isn't meant for that, was never designed for that, and isn't very good at it.

Not to mention that drywall layers should NOT be glued together in any case! Not even with construction adhesive, liquid nails, or anything else. Firstly, that probably is not even permitted by code, unless the second layer is also nailed or screwed in place: drywall is brittle and not very strong at all. If someone were to just glue up the second layer without nailing it, that would eventually de-laminate: the gypsum core would sooner or later peel away from the cardboard backing, due to the weight, vibration, humidity, etc. And secondly, there's no reason to do that anyway! Gluing layers of drywall together makes the acoustic isolation properties worse, not better, and serves no construction purpose either. It's a wast of time, money, effort, and glue.

On the other hand, Green Glue does not actually glue the panels together: As I mentioned, what it really does is to create a thin layer of damping in between the two panels of drywall, allowing them to still act individually (not as one single lump, which is what it would be if you really did glue them together). And it also keeps them loosely together, so that they can also act as one. There is a type of acoustic wave that happens in walls, called a "bending wave", which basically does what the name implies: as the wave moves across the drywall, it causes it to bend and flex in certain patterns that depend in the frequency. Since the entire panel does this all at once, moving in and out, it easily transmits those frequencies to the other side, where it acts pretty much like a loudspeaker cone, sending the sound waves out into the air. Therefore, the wall does not isolate at those specific frequencies where bending waves occur.

Green Glue is specifically formulated to fight that. It damps the motion of the bending waves, absorbing some of the energy and turning it into low-grade heat, which effective means that it gets rid of that movement completely. It does this since it is a soft, flexible damping compound with tiny air gaps trapped around it, and also because it is constrained between the two layers of drywall. Hence, it is technically known as a "constrained layer damping" compound, or CLD for short. There are other types of CLD, but they all work in the same way: by absorbing the energy of some types of waves that would otherwise get through the wall. In years gone by, people would use things like cork, roofing felt, vinyl flooring, even carpet underlay, inside their walls for the same reason: trying to use them as a CLD. They sort of worked, a bit, but nowhere near as well as Green Glue. Green Glue is the best, without doubt, as the guy in the video finally admitted. Quiet Glue Pro is also a good CLD, but it leaks messily all over the place, running and dripping.... as the guy in the vide also discovered! Sure, he saved 20% of the cost of Green Glue, but now he has to spend time and money cleaning up all the goop that dripped and ran everywhere, then keep on cleaning it up in the future as it continues to drip and run... So he didn't actually save any money at all! He lost both time and money by trying to substitute a second-rate product. It's VERY interesting that pretty much all of the literature for Quiet Glue Pro is dedicated to trying to show how the product is "as good as Green Glue"... in other words, the manufacturers themselves admit that they are trying to attain the standard of the best product out there. Why would they compare themselves to Green Glue if they did not realize that Green Glue is the best? That's sort of like Nissan trying to convince their customers that their cars as just as good as Rolls Royce, and even better because they are cheaper, go faster, and use less fuel! Don't get me wrong: Nissan makes some good cars, but nothing that is actually comparable to a Rolls Royce. Comparing your own product to the market leader is admitting defeat from the start. I've never understood that...

and the carpet adhesive seems to look and behave quite similarly in terms of texture and viscosity(in their unused state.)

So does raw scrambled egg! Get a bunch of eggs, break them into a bucket, mix up that goop really well, and wait a while until it starts congealing. You'll notice that the texture and viscosity is very similar to that of the carpet glue... You could maybe even market that product as "Yellow Glue Extreme", and show that it works just as well as Roberts carpet adhesive 3095! But that does not make it a usable carpet glue. Would you argue that the scrambled egg mix is a good carpet adhesive, simply because the texture and viscosity are similar?

Take a look at the Green Glue website: There is abundant, extensive technical information on how it works, backed up by numerous real tests done in very reputable, independent acoustical testing facilities, showing exactly what the results are, and what it really does. You can see which parts of the spectrum it affects positively, which parts it affects negatively, which parts it does not affect at all, and you can compare that to the musical spectrum that you need to isolate in your room. Can you do the same for raw scrambled eggs? Can you do the same for "Roberts carpet adhesive 3095"? Do they publish the same technical data that Green Glue does? Have they ever even tested their product in an acoustic test lab? Probably not, because they don't even attempt to market it as an acoustic product. So how would you know if it really does act as a CLD? And if it does, how would you know what frequencies it affects positively, and which ones it affects negatively? There is no data at all to tell you that, so it is impossible to know. What if it turns out that "Roberts carpet adhesive 3095" is fantastic as a CLD below 30 Hz, and wonderful between 300 Hz amd 500 Hz, but just happens to create a huge transmission issue (direct flanking path) between 40 Hz and 120 Hz, which is where most of the bass guitar and drum energy is? So by using that product, you would make your walls isolate WORSE at the most critical frequencies.

Here's one page from the many dozens available regarding actual Green Glue testing in an independent lab:
It shows pretty amazing results, actually. That's for a staggered stud wall with 2 sheets of 5/8" drywall on each side, and Green Glue in between on both sides. The results show an overall outcome of STC 62, and a VERY impressive 31 dB TL even at 80 Hz, the lowest frequency measured. According to IR-761, the very same wall construction WITHOUT Green Glue only gets STC-56, and only 24.7 dB at 80 Hz:
There's also a significant coincidence dip at around 2 kHz there, and clear resonance issues at 63 Hz. Green Glue is eliminating all of that, and improves the overall isolation by 5 points, which is pretty major. And which is what it claims to do. Not only does it eliminate the coincidence dip completely, it also produces a massive isolation PEAK at about 3,000 Hz, which is where a lot of musical instruments also have energy peaks. From the published data, it is therefore clear that this wall construction with Green Glue would be an excellent for somebody wanting to isolate a room for drums, bass, growling electric guitars, deep keyboards, and such like. Is the extra cost worth it? That's for each person to decide. If someone needs that very significant extra isolation boost, then yes, it is worth it. If they don't, then no, it is not worth it.

On the other hand, nobody on this planet has a clue what the performance graphs for "Roberts carpet adhesive 3095" are like, because nobody has ever measured them or published them! Does it REALLY work like a CLD? Nobody knows. Does it IMPROVE isolation in the low end, like Green Glue does? Nobody knows. Does it eliminate the coincidence dip, like Green Glue does? Nobody knows. Does it increase overall isolation by 5 points, like Green Glue does? Nobody knows. Or maybe it makes things WORSE at some frequencies? Nobody knows.

So, unless you want to pay the price to have that stuff tested in a reputable, independent acoustic lab, you will never know if your room is any good at all! You won't know if all that effort, time, and money made your walls isolate better, or not. You'll never know if it had unexpected negative consequences for some frequencies, or not. I'm sure you'll come back (like the guy in the video did) and say that his studio worked out great (understandable extreme psychological bias...), but he has no idea how much better it would have been if he would have just used Green Glue. He even admits that, indirectly... He KNOWS that he screwed up big-time by not using the right product, but he won't actually say that directly, because he is emotionally invested in his studio, and admitting that it doesn't isolate very well would NOT be a good way of advertising his services! He does not provide any objective isolation measurements, showing what isolation he ACTUALLY achieved... so nobody knows how well that compares to what he WOULD have achieved by using Green Glue, which really is known, and is well documented.

Sorry about the rant, and really, it isn't directed at you personally! Rather, as you mentioned, it is intended for anyone else who might find your thread in the future, so that they can make their decision on which way to go, based on real, solid, accurately measured, published data, not on the unqualified opinion with vested interests of a you-tube video maker.

If I had a dollar for every enthusiastic but wrong "How I Built My Studio" video on You-Tube, I'd be an awful lot wealthier! There's a huge number of those well-meaning but totally uninformed and ignorant videos, that do more harm than good, to be honest. They mislead people into building their studios using bad techniques, then wondering why things don't turn out very well. For example, all of those "This Is How To Float Your Studio Floor" videos that show plain stupid techniques, many of which are not just terrible acoustically, but also dangerous and illegal! Especially considering that the vast majority of home studios do not even NEED to float the floor, and doing so would make things WORSE. All that wasted effort and money.... Sigh!

Hopefully, you'll work your way through this issue, do some research on how acoustic isolation really works, get to understand MSM resonance and the four regions of isolation, learn about the equations, materials and techniques that actually do work, and save yourself a hell of a lot of money by doing it right, from the start, while also ending up with the best possible studio you can get for your money. That's what this forum is all about.

Here's an example of a studio that started off being built badly, but ended up being among the best in the world: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471 That was built by a forum member who realized he was in over his head and asked for help. Very smart guy. Here's an example of another studio that was designed correctly from the start, and achieves over 50 dB of isolation (measured in reality, not guessed), where the final tuning is currently in progress: http://www.johnlsayers.com/phpBB2/viewt ... &start=165

There are many more examples of studios built right, all across the forum. Here's a brief list of some that have been completed successfully by forum members: http://www.johnlsayers.com/phpBB2/viewt ... =10&t=5842 There's actually far more than that, but those are the ones where people have notified us moderators about the studio having been completed, or that we have noticed ourselves. It often happens that people are so happy to finish their studios, that they forget to tell us about them! So that's only a partial list of successfully completed studios on this forum. If you look around, you'll find many more. You'll also find a few "abandoned" threads, where people decided to NOT take our advice, and ended up failing. And you'll probably notice that ALL of the successful ones were carefully planned, carefully researched, carefully designed, then carefully built. In many cases, the really smart people realized they had made mistakes, so they knocked down parts of what they had already built, then re-built it correctly the second time. Here's one such case: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=17363

So I sure do hope you stick around on the forum, and build yours right, like the successful members!

- Stuart -

So much information! I wish I could start over, but I am only looking for moderate reduction in sound levels. I am nearly 25 and won't be living here much longer, and I really don't want to take everything down. Hopefully what I have now will help achieve my goals.

My biggest (and really, only) concern is the tenant that lives in the apartment on our second floor. Her apartment is localized to only a small portion of the second floor. Prior to construction of my room, I had my brother play my drums in my basement to see how audible it would be from her location. Surprisingly, all that is heard is a slight thud from the bass drum. She says that she thought it was 'somebody walking,' and the sound is not a bother, but i'd like to keep her as happy as possible so i'm aiming for just a little less thud in her apartment. The home is 120 years old, and the walls throughout the home are quite thick and dense, particularly the walls separating her apartment from the rest of the house. The house is 2500 sq ft, so there is a lot of space between the drum room and her apt, and I have placed the room as far from her as physically possible in the home.

Stuart, what do you suggest I do by looking at these photos? The drum room is completely free-standing, and has no contact with the existing structure. John's plans include insulation glued to the drywall exterior - should I do this? And should I place a door at the entrance next to the insulation pile? Will that complete the outer leaf somehow?


I've attached a layout of my basement as it stands right now, with some photos for reference. I'll take better photos tomorrow, as these were taken a few days ago and I’ve progressed a bit since. You will also notice bare existing framing in certain areas- this was from a planned basement remodel 11 years ago, which me and my father started when I was 13 (which is when I signed up on this forum!) parents ended up separating and construction came to a halt.



color legend for layout-
black - foundation walls (foundation seems to be huge rocks covered in plaster?)
orange - existing drywall construction (installed at some point in the last 120 years - mostly in good shape except for wall directly next to the drum room, which is in quite bad shape. you can see this in IMG_1458 behind the newly constructed inside-out wall. many parts of the wall on this side of the basement have had entire sections of drywall destroyed for various reasons)
red - brick / plaster wall with framing on top from uncompleted remodel project with dad
blue - beam
green - approx location on 2nd floor of tenant in question (I wrote 3rd in the layout photo - it should say 2nd)

Stuart, I’ve been going through the NRC PDF with the different assemblies - very interesting reading. They claim that a single wall assembly with 2 drywall layers on the outside and one inside with RC decoupling (page 191) is STC 53. I know STC is not relevant at lower frequencies but I’ll be practicing other instruments in here as well that are not as low end heavy (I realize that other instruments have low end as well.)

My question is: how does this apply to an already-decoupled room? From what I’ve read on this forum, RC is unnecessary when this is the case. The same wall, without RC decoupling is STC 36 or so, so I’m scratching my head. Which would apply here?

Which pages are you looking at? Please give me the page numbers, or the identifier just above the STC graph (they are all in the format "TL-93-xxx")

- Stuart -

On the subject of Green Glue, some great info above... I'm wondering if it really is by far the best method for insulating a new build room? I do see mixed opinions on it, but I think as has been highlighted, this often comes down to ignorance of the product and a misunderstanding of what it is. Lots of people write it off as expensive adhesive, which is just absurd I know.

I myself was looking at using TecSound, but am leaning back towards GG now. My biggest concern, as many people have I'm sure, is ensuring as little sound as possible (across the range of frequencies) gets OUT of my room, whether that be to neighbours or others living in the property. Is Green Glue the number 1 choice with this in mind?

I know a lot of the TecSound data comes from the manufacturers, but it SEEMS to present a good case for itself... it CLAIMS to be superior to GG, and it certainly has a considerable amount of mass (similar to lead sheets), which from Rod Gervais' book I know is of paramount importance. It also does seem to be used a lot in the industry from what I've been reading, but obviously I can't comment specifically on its effectiveness. Still, evidence would suggest it must be doing something? Versus GG though, I just don't know. I don't know why you'd opt for one over the other, as they do seem to be offering different things.

I know a lot of the TecSound data

You found some actual acoustic measurement data for TecSound? Please could you post a link to that. I looked for it before, but all I found was unsubstantiated claims and marketing hype.

I'm wondering if it really is by far the best method for insulating a new build room?

Green Glue is not insulation: As far as I'm aware, it doesn't have any insulating properties. At least, the manufacturers make no claims about that, nor have I seen any data on that.

but I think as has been highlighted, this often comes down to ignorance of the product and a misunderstanding of what it is.

Exactly. People just don't seem to understand it at all what it is, and what it does: It is a visco-elastic polymer that never hardens: It stays "gooey" and soft, because it has to! It works as a constrained-layer camping compound when correctly spread between two layers of partially flexible mass, such as drywall, MDF, plywood, OSB, etc. It works by acting on the bending waves that cause the layers to flex, as well as providing damping to other waves (sheer waves, for example). One of the strange properties of bending waves is that different frequencies travel at different speeds, and GG is really good at dealing with low frequencies.

On the other hand, TecSound is NOT a visco-elastic polymer, and is NOT a constrained layer damping compound! So comparing it to Green Glue is rather silly, actually. Sort of like comparing a fish to a bicycle....

Lots of people write it off as expensive adhesive, which is just absurd

Right! Especially considering that it isn't even an adhesive at all! Despite the name, it is not "glue" and was never intended to be used to stick things together. People who say that GG is an adhesive are just plain ignorant, and have no clue about it at all. Ignore them completely.

I myself was looking at using TecSound, but am leaning back towards GG now.

Modifying that to fit my above analogy, one could say that "I was thinking about buying a fish, but now I'm leaning towards buying a bicycle"... If you are hungry, you should get the fish. If you need to move about town fast and cheap, then get the bicycle! On the other hand, if you are both hungry AND ALSO need to get around town, then get both the fish and the bicycle!

Using GG does not preclude using TecSound, and using TecSound also does not preclude using GG. You can't use GG in direct contact with TecSound, of course, but you could use both of them in building up a "sandwich" of materials to create one of the leaves of your wall.

My biggest concern, as many people have I'm sure, is ensuring as little sound as possible (across the range of frequencies) gets OUT of my room, whether that be to neighbours or others living in the property. Is Green Glue the number 1 choice with this in mind?

Yes. No. Maybe. Always. Never. Sometimes! Sorry to be cryptic, but the question has no single answer. It all depends on what you are trying to achieve, what your budget is, what your space constraints are, what your structural limitations are, etc.

In most situations, you can get result that are pretty similar to what you would get with Green Glue, by simply adding an extra layer of 5/8" drywall to your leaf "sandwich". But that adds a lot more weight to the wall or ceiling, which might create a structural overload, and it also makes the wall much thicker, which might not be an option. GG is thinner and lighter, but more expensive. However, GG also has advantages in the very low end and at the coincidence dip, that the extra layer of drywall does not have.

Etc.

I know a lot of the TecSound data comes from the manufacturers, but it SEEMS to present a good case for itself... it CLAIMS to be superior to GG,

Same analogy: that's a silly claim, as it is the same as the bicycle claiming that it is superior to the fish! If you are hungry, the bicycle's claim would be rather hard to swallow, both figuratively and literally.... Why would a bicycle even bother comparing itself to a fish? Makes no sense.

Plus, there's a basic negativity when the manufacturer of one product says that it is "as good as" another, better known product: it's a direct admission that that the other product is pretty darn good! Doesn't seem to be a smart way to advertise to me: comparing yourself to the market leader is starting out by admitting that you are NOT the market leader... sort of backwards advertising! Imagine if the entire advertising campaign at Mercedes Benz was that their cars were "just as good as BMW"... Silly! Makes no sense. So you have to wonder why the manufacturer of a product would ever want to advertise like that, casting doubt on their own product by comparing it to another one that many people consider to be superior. Even if one is a fish, and the other is a bicycle. "Our bicycle tastes almost as good as their fish!". "Our fish can swim just as fast as their bicycle!".

and it certainly has a considerable amount of mass (similar to lead sheets),

So what? That's like saying "Bicycles certain do have big wheels, which fish don't have". An while that is totally true, it's not relevant if you need to swim underwater for long distances.... fins are a LOT more useful than wheels for that...

which from Rod Gervais' book I know is of paramount importance.

Mass is one of four aspects that are important for isolation. Mass, rigidity (stiffness), damping, and resonance. Each of those aspects has a DIFFERENT impact at DIFFERENT frequencies, and overall, together, as a group, they define the isolation characteristics of the wall:
As you can see, mass is just one aspect. Arguably, it is the most important overall, but NOT for all parts of the spectrum. If you add a lot of mass hoping to control low frequencies (below resonance), then you won't get very far! You should concentrate on the stiffness aspect down there, not mass. Ditto for the coincidence dip: adding more mass doesn't help you much there: but improving the damping certainly does! At resonance, and for about an octave either side, mass and damping are sort of evenly matched.

It also does seem to be used a lot in the industry from what I've been reading,

So are fish! So are bicycles!

Still, evidence would suggest it must be doing something?

Certainly it is doing something! It does have a lot of mass, and it is limp mass, which is very useful for SOME parts of the spectrum, as you can see from the above graph. But so what? Is mass what you need most in your design? Or do you need more CLD? GG won't give you mass and TecSound won't give you CLD...

I don't know why you'd opt for one over the other, as they do seem to be offering different things.

That's because the ARE very different things! People who compare them and try to say that one is "better" than the other, are falling for the same fish vs. bicycles trap. If you need a fish, then get a fish. If you need a bicycle, then get a bicycle. If you need both, then get both.

OK, so I'm exaggerating just a bit: This isn't quite as stretched as fishes vs bicycles: there are some valid comparisons, since both of these products do enhance isolation, and the effects are somewhat comparable, even if the products are not. A much more valid comparison would be TecSound vs Mass Loaded Vinyl: those really are directly comparable, as they are both the same concept: flexible, massive, limp mass sheet. If you must compare, then compare those two against each other, to see which is best.

You mentioned that one thing that has you worried is the expense of Green Glue, but do the math: There's not much difference, per square meter of wall area, when you compare the cost of Green Glue against the cost of TecSound! And there's an advantage to GG in that aspect: you can apply it more sparingly and still get good results. If you need to save a bit, then instead of using three tubes pere sheet of drywall, you can drop down to two tubes per sheet, or even one tube per sheet, and still have useful results. You can't do that with TecSound! If you only use it on half the wall or one third of thew wall, that0s the same as not using it at all.

I guess I'm not being much help here! I'm not giving you a concrete answer, that says "Use this, not that". As I mentioned at the start, it's not that simple. You have to decide what the priorities are for your build: what is the total isolation that you need, an what frequencies do you need it at? Then compare that against the results you would get from using EITHER TecSound OR Green Glue, OR both of them, to see what produces the results that YOU need in YOUR situation.

That's about the best I can do!


- Stuart -