soundproofing

Not something I know about but might be worth checking speakerplans.org - home of many a soundsystem nerd.

I'm no expert, but I've always understood that you need mass to cut low frequencies such as traffic rumble. There's not much mass in air.

There is a Studio Construction / Acoustics forum over at Gearslutz:

http://www.gearslutz.com/board/studio-construction-acoustics

I'm sure you'll find some good info on sound isolation there, but I expect most will recommend a thick concrete wall or two, which doesn't fit with your plans.

I know that there are some interesting products out there, such as sound reduction glue (!), but this wouldn't look so hot on your translucent wall.

http://www.greengluecompany.com (seem to be some useful articles on their site too)

Acoustics are a difficult thing to do a crash course in - you start hitting the nasty maths pretty quickly. I have friends who have done masters degrees in this stuff.

There's a lot of bumf on the net about acoustics, a lot of it is of questionable use and needs to be read with skepticism. Because the theory is so heavy, a lot of people have a trial-and-error approach to acoustics. Sometimes this gets good results, sometimes it doesn't, but it's usually hard to tell just from a net writeup. Amateurs also have a tendancy to mix up sound isolation with acoustic treatment, which is a different thing altogether (although obviously a lot of the concepts can be transferred between the two).

Here's my 10c for what it's worth - this is from someone with an engineering background and a strong interest in sound recording, but no specific training in acoustics. Make of it what you will.

The ultimate sound isolation barrier is a vacuum, which no sound of any frequency can travel through because there's nothing there to oscillate in sympathy with the soundwaves (you've probably heard that before...). But obviously this is difficult to do in practice. So most realistic sound isolation techniques are about working with materials to reduce the amount of sound transmitted from the source to the target. This breaks down into two areas - dissipation and decoupling.

HF audio frequencies travel through air with reasonable ease, but lose energy rapidly in heavier media such as water, and solid barriers (even when not designed with isolation in mind) will usually knock them out completely. If you look at a spectral plot of most real world sounds you'll see that HF waveforms contain a puny amount of energy. So HF sound isolation is all about dissipation - it's relatively easy to achieve on a budget, you just need something thick and heavy. You can tell from walking round your house that even duff stud partition walls will attenuate anything above about 300Hz and a good brick wall will probably bring that down to under 100Hz.

LF frequencies are much harder - partly because the bigger wavelength brings things like standing waves into play, but mostly because they just contain a huge amount of energy compared to HF. You need a lot of very dense material to dissipate that energy, so most LF isolation techniques rely on a mix of dissipation and decoupling. At the top end, people build complete floating rooms, where an inner room is suspended inside an outer shell on acoustic isolators (which act like shock absorbers). LF isolation involves using lots of neoprene and similar materials to make sure surfaces aren't rigidly connected to one another. People can also build resonators if they're having problems with specific frequencies - devices that oscillate in sympathy with incoming sound waves, which sucks energy out of them and stops it being transmitted onto the target.

If I was brainstorming on your idea of a reactive sound isolation surface, I'd look at maybe floating the room itself on neoprene, and decoupling it from the road via a rigid outer wall connected to the room via fluid dampers - you could then alter the damping co-efficient by changing fluid pressure. Or put two big plates of glass in and pump out the air between them. If you really want to make your head hurt you can look at control theory, which is all about system frequency response, damping factors, etc.

Here's some useful links:

http://www.soundonsound.com/sos/feb98/articles/soundproofing.html

http://www.studiooutfitters.com/isolation_tut.html

http://www.sota.ca/stc_info.htm

http://www.soundonsound.com/sos/jan01/articles/readerzone.htm

Would there be some way to do a kind of noise canceling thing? Turn the whole wall surface into a giant speaker that responds by playing a phase-inverted version of the ambient sound environment. Perhaps some kind of movable reflective sheet metal covering of the outer wall that is moved by a large speaker driver or hydraulic system attached to a microphone. The large moving reflective surface in itself would look pretty cool.

Well yes it would obviously be extremely tricky. But in a way you are not dealing with three dimensions if you are just trying to block the sound from outside one wall, it's just a plane. If it could be made to respond quickly to sound waves impacting the wall they should never get inside the room.

I have an extremely limited knowledge of acoustics but having worked in loads of recording studios and been in a few mastering rooms, it seem most modern recording recording studios are constructed so as too, isolate the sound within the room by building a room within a room so theres a cavity to reduce the amount of sound entering and escaping the space, creating a controlled space where reflection and resonances particular to the dimensions of the space can be dispersed using diffusion (panels of shaped foam) or controlling the resonances (bass traps etc.)

theres some stuff floating around on the net about absorption co-efficients, and what materials best absorb frequencies and at what densities.

thats all i know.

Gabba Flamenco Crossover said:

LF frequencies are much harder - partly because the bigger wavelength brings things like standing waves into play, but mostly because they just contain a huge amount of energy compared to HF.

Click to expand...

That's interesting, I'd have thought higher frequencies would have more energy. I guess that's on the assumption you have equal amplitude over all frequencies (a flat power spectrum), but maybe LFs are generally made, in music at any rate, at much bigger amplitudes than HFs?

Carbon dioxide's heavier than air, I think. (Edit: about 50% denser, apparently.) Colourless, obviously, and also odourless, so you'd need to make sure it didn't escape, otherwise there could be an asphyxiation hazard.

Edit edit: wouldn't it be AWESOME if there was an odourless, colourless and harmless gas that was denser than water? You could mix in a bit of oxygen so people could breathe it, and then fill a room with it and you'd be able to float around just under the ceiling. Cool.