h a l f b a k e r y
It's as much a hovercraft as a pancake is a waffle.

meta:

account: browse anonymously, or get an account and write.

 user: pass:
register,

# Retrofitting a Noise Barrier

Convert noise to heat
 (+5, -1) [vote for, against]

The Second Law of Thermodynamics basically says that most things are not 100% efficient at what they do. For example, electric power transformers are perhaps 95% efficient; the other 5% of the electricity that flows through them is simply wasted; it is converted from electricity to heat, and contributes in a small way to Global Warming.

In the average automobile when you step on the gas pedal some (maybe 30%) of the chemical energy of gasoline is converted into the mechanical kinetic energy of the automobile's motion; the rest is wasted as heat. And when you step on the brakes, ALL that kinetic energy is converted to heat; that is what brakes are designed to do (on the average car; I'm not talking about "regenerative braking" here!). Heh, one of the few times you can get 100% efficiency at doing something is when you want to generate heat!

When you want to build a building with some level of soundproofing in it, you usually use insulation of one sort or another. It has the ability to transmit sound poorly; therefore the sound energy that does not get transmitted ends up being converted to heat.

Now, what if you want to retrofit an existing building, such as your house, with greater noise protection? It could be rather expensive to rip the walls apart and thicken them with extra insulation! And what about the windows? You can't fill them with insulation yet! So, that's what this Idea is for.

It will still be somewhat expensive, but perhaps less so than reconstructing the walls of your house. The idea here is to surround your house with a greenhouse-style framework and then fill the spaces with piezo-electric panes of thin quartz. You wire the panes to simple electric resistors.

When a jet flies over the house and leaves a wake of tremendous noise, the piezoelectric panels convert the sound into electricity, which is immediately converted to heat by the resistors. So only a fraction of the noise penetrates to disturb your sleep. And of course since quartz is quite transparent, it doesn't interfere with seeing out the windows.

I'm of course quite aware that this Idea is half-baked at the very least because the conditions inside a greenhouse might not be acceptable in the summer. So it goes....

Perhaps simply adding a layer of piezoelectric window panes, over the existing windows, could be a less-problematic starting place. I'm only suggesting protecting the whole house because the place where I live had some special noise-reducing windows added, and now more noise comes through the (windowless!) front door than through the windows, when a jet flies over.

 — Vernon, Nov 24 2009

Almost as good as lead foil, and cheaper. [csea, Nov 24 2009]

QuietRock http://en.wikipedia.org/wiki/QuietRock
[xaviergisz, Nov 24 2009]

 The amount of energy provided your house from jets flying by is extremely trivial compared with any normal sunlight.

 Quartz windows would provide transparency in the ultraviolet light spectrum, but would be extremely expensive.

If you're trying to convert acoustical energy to heat, normal glass panes will do just fine. If your primary objective is noise isolation, try lead foil or high-density vinyl. [link]
 — csea, Nov 24 2009

 This must be the umpteenth idea for recovering energy from sound.

 It's all bollocks until somebody can actually tell me how much energy is represented by the noise impinging on a given surface.

My guess is that it's approximately bugger all (or negligible, in metric).
 — MaxwellBuchanan, Nov 24 2009

 For example, take the jet aircraft flying overhead, and make a few elementary assumptions:

 1) Assume that you live in a flightpath, and the jet passes over at a height of 1000m (which is low)

 2) Assume that the engines produce 50MW. Assume also that 1% of this winds up as sound (I'd be surprised if it's that much). That's 500kW of sound energy leaving the plane.

 3) Assume your house has an area of 500 square meters (ie, as seen from the plane).

 4) At a radius of 1km, the sound energy has spread out over an area of 4 x pi x (1000)^2 = 12,000,000 square meters.

 5) Therefore, your house will receive, at most 500,000 x 500/12,000,000 = 20 Watts of pure sound energy from the plane.

 In other words, even if you have a big house, and even if big jets are flying over it continuously at 1000m, and even if you capture 100% of the available sound energy, you're going to get 20Watts of power.

Vern, did you do *any* calculations?
 — MaxwellBuchanan, Nov 24 2009

While loudly pointing out that most systems are highly inefficient, he proposes that we dump gobs of money into flat sheets of quartz piezoelectric matrix. Really? We should encase our homes in fine glass panels. Ok. Just start by producing some numbers that show the relative benefit of quartz piezoelectric damper panels over their plain glass counterparts.
 — WcW, Nov 24 2009

This would work well for my neighbor the tinkerer who has many old cars and yells alot.
 — bdag, Nov 24 2009

 It seems a bit unnecessary/inefficient to convert the sound to electricity and then the electricity to heat; wouldn't it be easier to convert the sound directly to heat? see, for example, QuietRock. You could use that to clad the interior or exterior of the house.

For the windows, double (or triple) glazing works pretty well.
 — xaviergisz, Nov 24 2009

I'm sure I read in an old physics textbook some comparison of energy types involving the heat required to boil a cup of tea and someone shouting for years (or other ridiculous length of time). My apologies for my feelings of sloth and lack of backup calculations.
 — Jinbish, Nov 24 2009

I'd like to point out that brakes are not 100% efficient - a small amount of kinetic energy is converted to sound as the brakes vibrate :)
 — rocdoc, Nov 24 2009

 Double pane argon filled windows are surprisingly effective sound deadeners. Double pane evacuated windows are even better, but require periodic maintainence. If you're really dead serious about it, triple pane windows are also available.

If your house is decently thermally insulated, then your walls are already a fairly good sound dampner, if not, then spray in insulation will be cheaper and faster (as well as more building code compliant) then building a additional structure outside.
 — MechE, Nov 24 2009

or windows where the panes are not in the same plane, as used in studios. How much does a foot square of quartz optical glass cost these days?
 — WcW, Nov 24 2009

 [MaxwellBuchanan], I don't need to do any math when the sound inside the house, with windows and doors closed, approaches or exceeds100 decibels (eardrums have been perforated). The jets fly a great deal closer than a kilometer away, often perhaps only 100 meters away. These are US Navy F18A SuperHornets doing "touch and go" practice-for-carrier-landings, all day long. At least one person in the neighborhood is convinced that the more they complain, the lower and slower the jets fly. With their after-burners on, it sounds like.

 I'm not interested IN THE LEAST in extracting significant energy; I'm only interested in reducing the magnitude of noise inside the house, which was built about 1973 when the jets flying in those days had significantly less powerful/noisy engines. The insulation in the walls is reasonable for a temperate climate (and before the first Oil Embargo), but wildly inadequate for noise of the current levels.

And I don't mind playing with crazy Ideas like this, while thinking of possible options. I'm not aware that ordinary window glass has piezoelectric properties, but I do know that quartz has it. That's why I specified it.
 — Vernon, Nov 24 2009

 //I'm not interested IN THE LEAST in extracting significant energy; I'm only interested in reducing the magnitude of noise//

Aha! In that case, my apologies for misunderhending. But good professionally-installed triple-glazing, supplemented if necessary with inside on-the-wall insulation would be more practical, shirley.
 — MaxwellBuchanan, Nov 24 2009

 Hold on. Help me out here, Vernon. Will a Piezo type film on a pane, or other such arrangement, reduce the sound energy transmitted through the medium by any level? The reason I ask is that, without *any* real prior knowledge of the physical aspects I'm thinking:

 sound----> window reflection (echo?) <----absorbed window---> transmitted

 vs

 sound----> piezo-window reflection (-) <----absorbed piezo-window (+) ----> transmitted (-)

My concern, kinda brought up by [WcW], is that the energy absorbed by the piezo may well be negligible, compared to the physical effects of thicker glass or extra glazing layer.
 — Jinbish, Nov 24 2009

 [Jinbish], the detailed facts don't matter much in this case simply because I'm fully aware it is a crazy Idea and this is the HalfBakery. Nevertheless, it is a fact that flexing causes piezoelectric materials to generate a voltage. If the voltage is allowed to push a current through a resistor, then the energy represented by (amps * volts = watts) is energy that had to come from somewhere --in this case it comes from the effort to cause the piezo material to flex. In other words, the more flexing that can be converted to current-flow, the less flexing actually occurs as sound-transmission.

 This is quite analogous to hand-cranking a generator hooked up to an incandescent light. When the light is "OFF" it is easy to turn the crank; when the light is "ON" the resistance of the filament (the electrical load) is directly "felt" as a significant increase in difficulty of turning the crank. So, in this Idea, the resistors count as an always-ON "load", increasing the difficulty by which the quartz panes can be flexed.

One could imagine a variation of this theme whereby computers are added, to analyze the just-started flexings of the piezo plates, and to immediately/deliberately apply countervoltages to counteract those flexings, to cancel out the sound trying to get through the "greenhouse panes". It should be nice and quiet inside, no matter how many jets are flying around outside.
 — Vernon, Nov 24 2009

Thanks [Vernon], I realise I shouldn't have put the emphasis on *any* - (but i am no expert in piezos). I'm trying to picture a thought experiment with many miniature microphones/piezo transducers arranged in a matrix and reacting to the incoming transverse sound wave. I can't see the sound wave reducing by any degree...
 — Jinbish, Nov 24 2009

 //the detailed facts don't matter much in this case simply because I'm fully aware it is a crazy Idea and this is the HalfBakery//

[marked-for-tagline]
 — csea, Nov 26 2009

 [annotate]

back: main index