Foro Soundman2020

'nother Q Is it better if the two panels of sheetrock are touching, or not? I put up one panel, and then put GG onto the 2nd panel, and then nail the 2nd panel to the first. Now both panels are in contact with the GG. BUT - say I put up one panel, and then put GG onto the 2nd panel, not going all the way to the edges, and then put some rubber (?) trim around the perimeter of the 1st panel, so when the the 2nd panel goes up, the GG that is on it is not touching the 1st panel. Is that better? Or is it better to not have an air gap in between most (not all) of the panels?

Those gaps are air "springs", and also separate the panels, so they don't touch. It's rather complex, but as the panels flex and vibrate, you do NOT want them to act as a single, solid mass: you want them to act a bit independently, sort of "sliding" past each other at the microscopic scale. The random arrangement of the "glue" and the air gaps accomplishes that. Technically, the concept is known as "constrained layer damping", where the layers can move independently but are damped acoustically by the "glue", along with the air gaps. If the coverage was 100%, completely joining the panels across the entire surface, the constrained layer damping would not be very effective. Too much Green Glue would inhibit the damping at the frequencies that matter most. I wrote an article about Green Glue a few years back, that you might find interesting: The truth about Green Glue - Stuart -

Thanks Stuart. Green Glue is not glue at all I know! So, you want a gap between layers of sheetrock, ok that makes sense. But what doesnt make sense to me, is not having full coverage of GG on the panel(s). The way my brain is working... it's telling me that the areas in between the panels not covered by GG will not stop vibrations; that vibrations will still move through the panels in those spots. And that ALL vibration would be stopped if the entire panel was covered. I guess I am wrong about this?

Those small pockets are part of the system, and they are supposed to be there. Green Glue is not glue at all: it is not an adhesive, and is not meant to hold the panels together. It's entire purpose is acoustic. It is a visco-elastic polymer with specific properties that help it damp vibrations between the panels, and in vibrations moving through the panels. The random arrangement of the strings of green glue and the gaps between them is an important part of how it works. You do not want the panels to be tightly stick to each other... rather, you want the gunk to create a very small separation between the panels, so that they don't really touch each other. Also, the compound never really dries, and is not supposed to dry or harden (like normal glue would). It remains "tacky" and rubbery forever. I really wish they would not have put the word "glue" in the name, because it misleads people into thinking that it is an adhesive, and should be used like one, but that isn't the case. So just squirt out those strings of gunk randomly over the back surface, in swirly patterns, exactly as that video shows. One or two tubes per full panel of drywall (4' x 8') is about right. Don't spread it out or flatten it, or use a spatula.. just do it like they show, and you'll be fine...

Hi Thanks for the help in the other thread. I am ready to move forward. I have the green glue, and have a Q about how to properly apply. I watched this vid: https://youtu.be/RLtlcy5YDQM?t=67 It seems as tho the entire are is not covered. I assume it will spread out when the two panels are pushed together... but won't there still be small pockets of no glue? Is it not better to use a scraper to lightly scrape the glue over the entire area? Thanks!

also, MDF is nice and dense as well when it comes to adding mass. defintitely add the insulation into the air space.

I would suggest not using homasote here. That's great for making hangers, but isn't very dense, so not much mass... not a great material for isolation. Just go with two layers of drywall (sheetrock). The insulation in the cavity is a critical part of isolation. It does several valuable things: damps various types of resonance that go in on there, changes the way the trapped air deals with sound waves, decreases the speed of sound, makes the cavity seem bigger, from the point of view of sound waves, and a few other things. Leaving that out can cost you a large chunk of isolation. What you are creating is technically known as an MSM system (Mass-Spring-Mass), where the outer glass is one Mass, the inner leaf you are creating with the drywall is the other mass, and the cavity is the spring. It's a tuned system. It works something like the suspension on your car. Leaving out the insulation is equivalent to taking out the shock absorbers on your car... that would give you a terrible, very bumpy ride! Ditto with the insulation in your cavity. You might find this interesting, on how MSM works, so you can fully understand these recommendations, and build your isolation better: What is MSM? How does it work? - Stuart -

Thanks Stuart. seal everything around that window with abundant caulk... all gaps, cracks, joints.. everything Yep, did that. depending on how bad the problem is It's not bad, but there is some room for improvement. facing the room, I imagine Yes. studs in the gap to get a nailing surface all around the perimeter, then nail a layer of homasote to that, followed by also nailing a layer of drywall (sheetrock) on top of the homasote. Is that the idea? Yep. don't forget to first fill the cavity with suitable insulation of suitable density, as that will greatly increase the isolation of the system That's interesting. I thought the air gap with nothing there (but air!) would be the way to go. I guess that's wrong? Sound waves don't care how much you pay for your mass Bastards! Green glue - was considering that, but thought MLV might be better. This is why I ask! So, GG inbetween the H. and SR. layers is better? But it isn't cheap I am only doing two windows, 32 x 46, that's 21 sq ft. Based on what I see, two tubes covers 32 sq ft, which is more then enough here. That's $56 - you are right, that ain't cheap, but it's relativeley nothign. Thanks!

I maybe didn't fully get what you are proposing, but a couple of key things in closing off that window: First, seal everything around that window with abundant caulk... all gaps, cracks, joints.. everything. If you can replace the glass with something thicker, that also might be worthwhile, depending on how bad the problem is. if it is really bad, consider replacing the glass with a thick pane of acoustic laminated glass. On the other hand if the problem isn't too bad, and you just need a few extra dB of isolation, the just sealing it should be enough. Gor the second leaf you propose (facing the room, I imagine), it I understand you correctly you plan to put some studs in the gap to get a nailing surface all around the perimeter, then nail a layer of homasote to that, followed by also nailing a layer of drywall (sheetrock) on top of the homasote. Is that the idea? If so, don't forget to first fill the cavity with suitable insulation of suitable density, as that will greatly increase the isolation of the system. In this case, mass is your friend, so two layers of drywall would be better, and get the thickest stuff you can find. 2 layers of 19mm would be great. Here too, seal up the edges of each layer right as you put it on. MLV is mass, yes, but it is very, very expensive mass. Sound waves don't care how much you pay for your mass: they only react to the mass itself. So get the cheapest, most dense mass you can find. Usually that is sheetrock. Yes MLV is also flexible, and th

I am thinking of closing off the windows in my studio - don't need them, and I can hopefully get rid of some road noise, such as trucks and motorcycles. I am thinking of a layer of Homasote, and a layer of sheetrock. Since there is some depth to the frame, I was going to add two studs, and nail the Homasote/sheetrock combo to the studs, and then caulk the perimeter. This would create an air gap, which I assume would work well. Should I put a layer of MLV in between the Homasote and sheetrock? Thanks in advance.