"Soundproofing" a window...?

[MatrixClaw]

Okay - so I realize I'm not going to be able to actually soundproof anything, but I'd like to get far more isolation out of my room than I am now...

I recently put up all of the acoustic treatment in my music room (combo mix/tracking room) and it sounds surprisingly great in there, despite its small size. However - I have a drum set in the room and it's a little too loud for my liking, when standing outside of the house. Unfortunately, the room has a front-facing window that (thankfully) seems to be pretty tamed by the curtains I've hung in front of it, as far as acoustics are concerned, but too much noise escapes out of it for me to feel comfortable playing loudly in the room and not bothering neighbors once it gets dark.

I was thinking of just going to the store, buying some thick, dense, foam and shoving it in the window so it seals tightly, but I wanted to see what other options I have. Unfortunately, the window is pretty large (5x5'), and while I have plenty of Roxul panels left over from my treatment, I'm not really sure that filling the window with them is going to do much in the way of preventing sound from escaping. Plus, it'll be messy if I ever need to remove it.

Obviously, I'm not looking to perform a miracle here, just hoping that I can stand in front of my house and it sounds like I'm listening to loud music, rather than standing in the room with the drum kit. The window is double-paned, not sure on thickness - I assume using something thicker isn't going to be very economical for the return in isolation I'd get?

Any advice would be appreciated!

[Soundman2020]

Think of it this way: You probably have a sponge in your kitchen or bathroom, since you know that sponges are really good at soaking up water, right? So try turning on the water, holding the sponge over the end of the tap, and see how well it stops the water flowing out of the tap...

Putting a porous absorber, such as Roxul (mineral wool), fiberglass, foam, or anything similar over your window will be about as effective at stopping sound getting out, as the sponge is at stopping water getting out....

That's not what porous absorbers do. They are great at "mopping up spilled sound", just like a sponge is great at mopping up spilled water. In other words, porous absorbers are good at "damping" acoustically, but lousy at isolating.

As a test, go to your hardware store, get a piece of mineral wool, wrap it in a piece of fabric, and hold it up against your ear.... can you still hear what is going on around you in the store? Yep, you sure can.... (The fabric is just so that you don't get an ear full of mineral wool fibers, which might not be very pleasant! )

OK, so what's the answer?

There are only about four ways to stop sound getting from "A" to "B". 1) You can build a barrier so massive that sound waves cannot make it vibrate. 2) You can build a barrier so rigid that sound waves cannot make it vibrate. 3) You can build a barrier so viscous that sound waves are fully absorbed (damped). 4) You can remove all paths that sound could take between "A" and "B", including air (in other words, create a vacuum).

Unfortunately, in the real world none of that exists. There is no such massive material that is so massive that it can stop all sounds. There is no such rigid material that is so rigid that nothing can make it vibrate. There is no such viscous material that can absorb sound totally. And there is no such thing as a perfect vacuum, not even in outer space. That's why we say that "soundproofing" is actually impossible. All you can do is to reduce the level of sound as it passes from "A" to "B".

But there is one sort-of exception: 5) You can combine certain things from 1, 2, 3, and 4 above, to build a "tuned filter barrier" that prevents some sound getting through but allows others through, in the same way as a tuned electrical circuit stops some frequencies getting through while allowing others. That's how studio walls are built, and that's the same concept you need to implement in your window. There are various ways of achieving this.

But what you should do first of all, is to measure how much isolation you are getting right now, and how much extra isolation you need, in terms of decibels. A simple sound level meter will do that for you. So get someone to play a certain rhythm on the drums over and over and over, while you measure the level inside the room, and outside the window, one meter away from it (about three feet). The difference between the two levels is how much isolation you have right now. Then walk away down the street slowly while watching the meter, until you judge that the level of drumming you are hearing is acceptable: That's how quite you have to be. The difference in the two readings is how much extra isolation you need. Based on that, we can help you design a "window plug" and other things to do, to reduce the noise level outside to the level you want.

Of course, all the above assumes that the window is the weak point: there might also be other weak points where sound is escaping, that you'll only find after you have built the plug and put it in place.

- Stuart -

[MatrixClaw]

Think of it this way: You probably have a sponge in your kitchen or bathroom, since you know that sponges are really good at soaking up water, right? So try turning on the water, holding the sponge over the end of the tap, and see how well it stops the water flowing out of the tap...

Putting a porous absorber, such as Roxul (mineral wool), fiberglass, foam, or anything similar over your window will be about as effective at stopping sound getting out, as the sponge is at stopping water getting out....

That's not what porous absorbers do. They are great at "mopping up spilled sound", just like a sponge is great at mopping up spilled water. In other words, porous absorbers are good at "damping" acoustically, but lousy at isolating.

As a test, go to your hardware store, get a piece of mineral wool, wrap it in a piece of fabric, and hold it up against your ear.... can you still hear what is going on around you in the store? Yep, you sure can.... (The fabric is just so that you don't get an ear full of mineral wool fibers, which might not be very pleasant! )

OK, so what's the answer?

There are only about four ways to stop sound getting from "A" to "B". 1) You can build a barrier so massive that sound waves cannot make it vibrate. 2) You can build a barrier so rigid that sound waves cannot make it vibrate. 3) You can build a barrier so viscous that sound waves are fully absorbed (damped). 4) You can remove all paths that sound could take between "A" and "B", including air (in other words, create a vacuum).

Unfortunately, in the real world none of that exists. There is no such massive material that is so massive that it can stop all sounds. There is no such rigid material that is so rigid that nothing can make it vibrate. There is no such viscous material that can absorb sound totally. And there is no such thing as a perfect vacuum, not even in outer space. That's why we say that "soundproofing" is actually impossible. All you can do is to reduce the level of sound as it passes from "A" to "B".

But there is one sort-of exception: 5) You can combine certain things from 1, 2, 3, and 4 above, to build a "tuned filter barrier" that prevents some sound getting through but allows others through, in the same way as a tuned electrical circuit stops some frequencies getting through while allowing others. That's how studio walls are built, and that's the same concept you need to implement in your window. There are various ways of achieving this.

But what you should do first of all, is to measure how much isolation you are getting right now, and how much extra isolation you need, in terms of decibels. A simple sound level meter will do that for you. So get someone to play a certain rhythm on the drums over and over and over, while you measure the level inside the room, and outside the window, one meter away from it (about three feet). The difference between the two levels is how much isolation you have right now. Then walk away down the street slowly while watching the meter, until you judge that the level of drumming you are hearing is acceptable: That's how quite you have to be. The difference in the two readings is how much extra isolation you need. Based on that, we can help you design a "window plug" and other things to do, to reduce the noise level outside to the level you want.

Of course, all the above assumes that the window is the weak point: there might also be other weak points where sound is escaping, that you'll only find after you have built the plug and put it in place.

- Stuart -

Stuart,

Thanks for clarifying. It didn't make sense, from a common-sense standpoint, that using any kind of acoustic insulation would make much difference, which is why I was thinking dense foam (I'm talking that really hard industrial-strength styrofoam/insulation board, not Auralex junk), that could be cut slightly larger than the space and pushed into the opening for a tight seal. I've actually done this before in a previous residence to block sound from coming INTO the room, and it worked very well - though I never really checked the sound level outside of it, as that wasn't a concern. I was also thinking drywall could work well too, but I'm not sure how I'd seal it around the edges, without caulking the panels in, because it's not going to form to the size of the window, like foam would. It'll just fall apart.

Forgive me if I sound rude - but what advantage would measuring the decibel level give me? I understand its purpose in a new studio build, where you're trying to achieve a certain level of acceptable isolation and whether it'd even be possible within budget, or just to educate us on what kind of difference the "plug" makes in the end, but in my case, I need to do something about it. Whether the ideal isolation level can be achieved or not, anything is better than nothing. I really can't imagine something like this being very expensive, so budget shouldn't be much of an issue - obviously I'm not going to build an entire wall to place over the existing wall - and the "plug" needs to fit inside the window sill, with minimal protrusion outside of it, if any. I have about a 60x60x3" or so area to play with (can go a little longer on the depth, because I have curtains in front of the window that will hide it being ugly, so the best solution that will fit in that area is what I'm looking for, assuming it doesn't cost some outrageous price for some unknown reason.

Thanks!