Towards a better tinyhouse

Inventing to freedom?

Vacuum insulation

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Michael Janzen has a post up up about the limits of portable tinyhouses, and it reminded me to do that post about vacuum soundproofing panels.

Basically, vacuum soundproofing panels are totally awesome, very lightweight and much cheaper than equivalent soundproofing methods. They can be made with existing production machinery used to make thermal vacuum panels. They are also not a new idea, depending on what is basically newtonian physics.

One of the major differences between tinyhouses and rvs is the resultant acoustic environment produced inside. One of the major complaints about FEMA trailers (RVs) is the poor soundproofing that they had. So it is important to have this feature. The problem is, normal soundproofing is *heavy*. Very heavy. I previously mentioned decoupling, and damping.

Here are 2 patents on them:

As you can see from the patents, what we have here is a case of extreme decoupling, for the most part, since no (or very little) air results in very little transmission in that way. But, what about those support columns? Those long glass or zirconia rods (long compared with their diameter)… As mentioned in the patent, they, or the border around the panel in the case of the second patent, conduct almost all the sound, as you would expect.

Basically, when a sound wave approaches the end of the column, where it meets the metal sheet, you can think of a pressure being briefly exerted on the column. You can ignore the propagation of sound waves, the wavelength, etc. here because the speed of sound is so high, and just think about this in terms of newtonian mechanics. So the column starts to accelerate in the opposite direction, transferring some movement to the other sheet of metal on the other side of the column. The heavier the column is, the less it moves.

If you have read about soundproofing, you may recall that for something like a concrete wall, which only provides soundproofing by virtue of it’s mass, if you multiply the weight by 2 while keeping the area of the wall the same, the amount of soundproofing you get goes up by about 6 dB. The same applies to the support columns here.

The amount of energy that gets transferred through the column is going to go up sort of linearly as the diameter of the column in contact with the metal plate goes up, too. More area means more force is exerted on the column.

So… clearly we want to maximize the weight of the column, while minimizing the diameter, where it meets the plate. That’s why these people are using relatively long, thin glass rods. The longer the rod is, the better the thermal isolation is, too, or course. So for a thermoacoustic barrier, long glass rods might be the way to go, but for just soundproofing, you can make the columns widen in the middle, for example, instead of making them longer. That would give you a thinner panel, and still okay thermal performance. That would make them stronger, too. You can always add some foam to the other side if you want.

The material used as the plates also matters, the stronger it is, the smaller you can make the ends of the support columns. If you multiply the thickness of the metal by x (or the tensile strength by x), you can divide the support column diameter by x, more or less, until you get to the point where the column is thinner than the material is thick, and the structural characteristics change, and it is more like a needle pushing through the material, than like a hole punch. Also, thicker material is going to be more expensive, so there’s going to be a design optimum there somewhere.

You’ll also notice both these people made these panels by hand, all you really need is a way to shape the metal, a vacuum pump, sealant tape, maybe some sealant and a way to evacuate and seal the panel.

For Reference, a 65 dB wall would otherwise require 4 sheets of drywall, decoupled, and with 2 of the sheets using green glue between them, to achieve!

A normal tinyhouse wall is probably more like 35-40 db, and an rv might be 12-18.

But, the obvious problem here is the potential for leaks. Having worked briefly with low vacuums like this before, I think they would be pretty easy to patch. You can even get “leak detectors” that use the sound emitted by a leak to track it down, then just put some sealant gunk on it. But you should definitely plan for the inevitability of leaks, making the panels readily accessible and removable, etc. Man they would be really sweet, though, especially some factory made ones that were really unlikely to leak, they would just be so much cheaper and lighter than any other form of soundproofing can achieve.

Given the market for soundproofing products, you really have to wonder why they are not in production yet. Thermal vacuum panels are, so the leak issue can be overcome. However, when a thermal vacuum panel fails, it still provides a good bit of insulation, whereas when an acoustic panel failed, all your soundproofing would go out the window. So you definitely need to be able construct your building or whatever to be able to easily repair and replace panels not if, but when, they fail. Maybe that’s why they aren’t in production, but that could be accomplished in a tinyhouse. Suppose you glued some cosmetic material to them, and then put up something like the usual 2×4 wood framework of the tinyhouse (but made to have shear strength, which plywood usually provides), to attach the panels to the outside of, basically cladding the tinyhouse with them where the wall sheathing would normally be. They could serve as both the outer wall, and the inner wall. Well, I bet you could design them, or a panel system so they could be leaned against, but maybe it would be better to have an inner layer of wooden wall with 1/4 (or even 1/8?) plywood or something, to prevent a force being exerted on the back of the vacuum panels by people leaning on them, etc.

You could make a tinyhouse so light it could be pulled with a normal car, like an RV, that would be a plus, and it would make a great office, very nice and quiet.


Written by gregor

August 21, 2010 at 01:42

Posted in Uncategorized

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