h a l f b a k e r y
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If you ever heard a jet fly low over your house, you probably heard quite a bit of
noise. But if you were in an automobile with the windows up, and a jet flew
equally low over the car, you likely would notice rather less noise. Therefore the
glass ordinarily used in the automobile is simply better
than the glass ordinarily
used in house windows, for blocking noise.
I think part of the secret is that automotive glass is "safety glass", two layers
that are bonded together (the glue or whatever counts as a third layer) to
drastically reduce the chance of shattering. Being a fairly hard substance,
glass normally conducts sound easily --but that bonding layer, in automotive
glass, is most certainly not a hard substance. Much noise simply gets
absorbed/blocked by it.
So, the Idea here is that we should use safety glass for house windows --not so
much for safety, though, as for noise reduction. We could even use thinner
layers of glass than are used in cars, bonded together (making up one "pane" of
the double-panes or triple panes used in thermally insulating windows).
Because we want the sound-absorbing layer more than we want thick glass.
Saflex® interlayer provides superior noise reduction capabilities compared to ordinary glass [xaviergisz, Sep 04 2014]
Bisn ® PVB interlayer film provides good sound insulation [xaviergisz, Sep 04 2014]
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||Double glazing works very well for noise. Even better is non-
parallel double glazing. In a regular double glazed window,
the two panes are separated by an inert gas, but this still
allows one pane to compress the gas and pass on vibrations
to the next one, like a drum. If you angle one pane relative
to another, then a component of the energy is directed
toward the wider end. Where you can put a sound absorbent
material. They use this technique in recording studios.
||"Double glazing" is just another way of talking about the "double
panes" already mentioned in the main text.
||On triple pane windows I've heard that if the gap
between one pair of panes is different than the gap
between the other two that the two gaps will block
different frequency ranges so overall noise
reduction will be better than a standard tipple pane
window. I didn't see any data saying how much of
an improvement this would make or how much
different the spacing should be.
||The only glass in a car that is laminated is the windshield.
In that case it is two pieces of regular glass laminated with
a piece of plastic. Some cars also have a plastic layer on
||All the side and rear windows utilize tempered glass which
is one single piece of glass. It is thicker than your typical
window glass by about double. I suspect this difference in
thickness has more to do with the dampening of noise than
||the BMW 5 series used to have double glazed side windows,
ostensibly to reduce cabin noise. They dropped it in
subsequent generations because the thermal insulation was
too good, meaning it was a pain to de ice, and if it was cold
enough outside, would re-ice as you drive.
||One of the reasons car glass is good at deadening
sound is that it's usually held in a rubber gasket,
rather than being fixed rigidly. This helps to absorb
vibrations imparted to the glass by noise, and
prevents them being transmitted to the metal
||Laminated glass is not especially good at blocking
sound, because the laminating material has too high
a modulus to absorb much of the energy.
||Is the problem measurable?
||Car interiors are noisy and your tolerance for noise may increase while driving, effectively cutting out some jet noise. Or, jet noise may be acoustically occluded by the car noise. There may be perception issues here.
||//There may be perception issues here.// Story of
my life, mate.
||I think Vernon is right that cars are more quiet than houses
when they are not moving and the engine is not running.
The laminate glass idea is flawed because only the front
windshield is laminated. The rest is tempered.
||Maybe it's the tempered glass. Tempered glass is very hard,
and is under some kind of internal tension; when it breaks,
it all breaks at once. Maybe this bounces sound better?
||I think, though, the fact that a car is practically
hermetically sealed has more to do with it. Houses have all
kinds of gaps and cracks and windows and doors that don't
fit right. Holes let the sound in. Cars are designed not to
have holes. That's why you can tell immediately if the
window is rolled down a bit or if the door is ajar on a car.
||//than houses when they are not moving
||They move quite a lot here sometimes. Ok, I raise you one double-glazed window with jelly in between the panes.
||Good damping qualities and you can eat it in hard times.
||Hand crank or little rocker switch to open and close window ?
|| / Automotive Glass for House Windows /