Studio walls from Tyres | John Sayers’ Recording Studio Design Forum archive

Hi there Dave, and Welcome! :) That is indeed a strange question! And interesting, too. But first, the myth:

I've read of people using car tyres to float studio floors,

So have I, but never successfully! It's no easy job to correctly float a floor, requiring careful calculation of resilient deformation, loads, areas, thicknesses, resonatn frequencies, and suchlike. Car tyre rubber does not fit into this at any point, since its resilient properties are way out of line with what typical studio floors need. I've heard many rumors of people trying to float their floors on tyres, but I've never come across a documented case where it was actually done and worked. (Although there are a couple of documented cases right here on the forum where it DIDN'T work! :) So I think we can safely lay that myth to rest, unless someone can come up with some actual proof, including convincing acoustic tests, that it can work. So on the main question:

has anyone heard of anyone using car tyres, either whole or cut across the diameter, for a studio wall?

Personally I haven't heard of that either, and I can't see how it would even be of any benefit. Studio walls are 2-leaf MSM systems, that are based on the principle of resonance. You tune the resonant frequency of the wall to be at least an octave lower than the lowest frequency you need to isolate, you choose the mass, density and air cavity depth suitably to obtain that frequency and the level of isolation you need, and you are done. The math isn't hard. But I can't figure out how you would even incorporate full or halved tyres into that system at all! The wall would have to be incredibly thick to even fit a tyre inside it, so you'd need to start out with a very large space where three-foot thick walls would not be a problem. With most home studios, real estate is at a premium and people are trying desperately to scrounge out every last fraction of an inch they can get, by minimizing wall thickness! So I can't see most studio builders even being interested in making a wall three feet thick just so they can use tyres, when a typical wall is less than one foot thick. Second is density: from what I can find on-line, the density of tyre rubber seems to be around 450 kg/m3, which is considerably lower than drywall (plasterboard), so there's no advantage there at all, even assuming you could figure out how to build such a wall. I suppose you might be able to use granulated tyre rubber as a filler between two layers of drywall, plywood, OSB or MDF, but due to the low density, it doesn't seem to be a very attractive proposition. I'm not sure how much that granulated tyre rubber would cost you, but I'd take a wild guess and say that a simple sheet of plain old drywall would be cheaper, kilogram for kilogram, and an awful lot easier to work with.

I was thinking that this would not only provide mass

Yes, but not enough of it. As I mentioned above, the density of tyre rubber is around 450 kg/m3. Drywall is about 685 kg/m3, MDF is around 750 kg/m3, brick is around 2000 kg/m3, and concrete is around 2300 kg/m3. So to get the same mass (surface density) you'd need to have a layer of tyre rubber about 50% thicker than drywall, over 4 times thicker than brick, and 5 times thicker than concrete. It has some mass, but nowhere near as much as common, inexpensive building materials.

but would also flex,

So do drywall, OSB, plywood and MDF! But in reality you don't really want a wall to flex much, since some parts of the spectrum are controlled by rigidity (stiffness), not flexibility. If one leaf of a wall flexes greatly, then it is creating large rapid, cyclical changes in the air pressure inside the wall cavity, which in turn is causing the leaf on the other side to flex in sympathy. Another word for "rapid changes in air pressure" is "sound wave"... :)

and might contribute to bass trapping?

I'm not so sure that it's a good idea to use your isolation walls as bass traps! Bass trapping is best accomplished inside the room, with treatment, not outside the room. If you let bass through the walls, then you aren't isolating it! You are allowing it to escape. I suppose if isolation wasn't needed much for a studio then you could do that, but I don't see the point for typical home studios today, built with modern methods. Finally, there's the issue of data. There really isn't much scientific data on the acoustic properties of scrap car tyres. There is some, but it isn't very exciting. I found a paper that was published in Spain last year, and this is part of their data:

Image not preserved: Sound-absorption-of-tyre-rubber.jpg

They tried sintering some test panels from tyre rubber granules, in several different ways, and those are the results. Frankly, even ordinary commercial carpet has better acoustic properties, and carpet is already pretty lousy for acoustics! Not that the absorption coefficients tail off drastically at low frequencies, so it doesn't look like they would be much use in bass traps... Part of the conclusion of that paper says: " It is demonstrated in previous studies that rubbers and fibers are not good sound absorbers when working independently with small thicknesses. "

The shape could aid diffusion, particularly if tyres of different sizes were used?

How would you choose the upper and lower diffusion cut-off frequencies, if you have no control over well depth and width? It seems to me that the tyre tread would only work at very high frequencies, and the tyres themselves at very, very low frequencies, but it's really hard to predict what effect they would have. About the only use I can think of is to maybe stack some halved tyres against the walls, floor to ceiling, and pretend they are poly-cylindrical diffusers, but I think plain old sonotubes are a lot cheaper, a lot easier to work with, and rather more aesthetically pleasing!

Or ...er... not?

I think I'd go with "not"! :) At least until someone figures out how to makesscrap tyres into acoustically useful products. I'm not saying it can't be done, but so far nobody seems to have done it, and I'm not at all convinced that such a product would be cheaper or acoustically better than other materials that are known to work well. I hope that's not too disappointing as an answer... It sure was an interesting question, and got me doing some research that I would never have thought to do if you wouldn't have asked, so thanks for asking! - Stuart -