What material is best at absorbing sound?

There's been some debate on the Naked Scientists forum over how best to sound-proof the noise of a chainsaw. Physicist Jess Wade explained which materials aborb sound the best...

Jess - There's a few different ways you can do it and it depends how much money you want to spend, really. You can obviously get materials that are better at absorbing sound, kind of soft materials, fabrics, cloth that you wrap around things, when you go into soundproof places. You can get materials that are really good at damping sounds, so they're materials that don't vibrate. When you go into a recording studio, you see those kinds of funny structures on the walls and they're really, really good at just making sure things don't vibrate and you don't hear anything. Or you can do incredibly elaborate things where you kind of build a floating room within a room and you isolate it so that sound can't get through, and can't come in and vibrate the little hairs in your ears and tell you your ears and your brain that you're hearing something awful. I think probably the most effective way to do it for a chainsaw, which is obviously intermittent,, and you don't want to invest tens of thousands of pounds into soundproofing, is to just wear earplugs or to try and get noise canceling headphones, because they do a pretty good job and I don't think you'll be using the chainsaw 24 hours a day and justify the cost of soundproofing something elaborately.

Chris - That's true. Although you know, we went to the Hello Tomorrow summit in Paris last year, and I met a guy there who has made noise canceling windows for houses, and it's the real deal. And what he does is, he has a system that can detect the vibrations of sound waves hitting the window, and he can detect and process this so fast that the sound waves don't even make it through the window. What they've done is to work out what the sound waves look like and then put back into the window, the mirror image of that sound to cancel out the sound before it's made it to the pane on the inside. And as a result you don't hear anything. And he reckons they can knock the sound coming into the house down by maybe 60-70 decibels. You can't hear the traffic in the street outside, for example. It's costly and it's quite expensive to run in terms of electricity. It's not got a zero kind of electricity footprint cause you've got to obviously put the active sound into the windows, but cool. Yeah? I thought that was really interesting.

Jess - You could, kind of find some polymer that can be used to generate electricity from sunlight and a transparent one that you could have on the window to generate the electricity to power that. So there's ways to get around it being power hungry.

Chris - Yeah, I mean the only downside is that sound finds its way into houses through routes other than just the windows as well, doesn't it? So you've to sort of, air proof your house.

Jess - Yeah, you've got to block your chimney, your plugs and everything like that.

Chris - It does become a law of vanishing and diminishing returns. I fear.