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Darren New <dne### [at] san rrcom> wrote:
> I think the way it works is this:
>
> X-rays actually are small enough to go between the atoms (altho they'll
> still interact with the electrons, which is why metal still stops them,
> having a "sea" of electrons on the surface).
>
> Visible light hits (most) atoms and gets absorbed, reflected, etc.
>
> Radio waves are physically bigger than the atoms (and the whole house, for
> that matter) so they basically are ghosting along like a car through air.
There's another thing that takes effect in these scenario, and that's quantum
effects: Electromagnetic waves transmit energy in "standardized" packets, with
the energy of a single packet being dependent on the wavelength. Similarly, the
energy levels in whatever it interacts with are quantized, and in order to
interact, the EM packet's energy dose must be fitting to bring the "target's"
energy to a higher "valid" level.
Radio waves are too weak to interact with atomic particles presently bound to an
individual atom, and therefore can only interact with free electrons - which is
why they zip straight through insulating materials without effect, but readily
interact with conductors.
Visible light waves are strong enough to "kick" around electrons within an
individual atom, but they're too weak to kick it "loose" and impart any excess
energy to it as kinetic energy, so they are particularly picky what materials
they will interact with.
X-Rays are strong enough to kick eletrons loose from atoms, and any excess
energy will simply be converted to kinetic energy of the electron, so they will
interact with everything, just depending on the material density.
> If you have a stiff screen with water waves going thru, waves much smaller
> than the holes will go thru, and waves much bigger than the holes will go
> thru all the holes at once and reform on the other side. Waves bigger than
> the holes but smaller than two holes will mostly bounce.
Try, and you'll see it's not true. In water, the ratio of pass-through vs.
bounce is primarily a matter of size of holes vs. size of non-holes.
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clipka wrote:
> There's another thing that takes effect in these scenario, and that's quantum
> effects:
Thank you for that excellent clarification. :-) Or, rather, correction.
--
Darren New, San Diego CA, USA (PST)
"We'd like you to back-port all the changes in 2.0
back to version 1.0."
"We've done that already. We call it 2.0."
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> Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a wavelength
> of about 170 cm.
>
> Question: Since the doorway to be bedroom is less than 170 cm wide, does
> that mean those waves can't leave the room?
No. Anyway sound goes through solid things as well as air so even if it
couldn't go through the gap it would go through the wall itself.
Try producing a tone that has the exact wavelength of the distance between
your speakers and the doorway :-)
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scott wrote:
>> Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a
>> wavelength of about 170 cm.
>>
>> Question: Since the doorway to be bedroom is less than 170 cm wide,
>> does that mean those waves can't leave the room?
>
> No. Anyway sound goes through solid things as well as air so even if it
> couldn't go through the gap it would go through the wall itself.
OK... but presumably the velocity of sound inside a brick wall is
different to free air, so there would be some kind of diffraction effect?
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>> Question: Since the doorway to be bedroom is less than 170 cm wide, does
>> that mean those waves can't leave the room? Or does the fact that it's
>> more than 170 cm tall negate that?
>
> I think you have a misconception of what wavelength means. The misconception
> probably comes from those 2D drawings of wave functions.
>
> A sound wave (nor an electromagnetic wave for that matter) is not some
> kind of sine wave which goes through the air. The sine wave function you
> see drawn on a picture is just the representation of the function which
> tells which direction the wave is "pushing" at certain point (and how
> "strongly" it's "pusing"). The sine wave drawing is just a graph which maps
> time to amplitude ("strength" of the sound wave), it's in no way meant to
> represent the *physical* appearance of a sound wave.
>
> A sound wave is simply a phenomenon of air molecules pushing (and pulling)
> adjacent air molecules. The phenomenon traverses through air. The maximum
> strength at which this "pushing" happens is the amplitude of the wave, and
> the rate of change between "pushing" and "pulling" is the frequency. The
> distance between two "pushing" peaks is the wavelength.
...all of which is true. However, a simple experiment with a wavetank
quickly demonstrates that, for some reason that I don't comprehend,
large waves won't go through small gaps, and yet small waves will. This
is the precise opposite of what you would expect, but the results are clear.
(This also explains why animals that use echo-location use such
high-frequency sounds; they give better spatial resolution. I might even
go as far as to say that's why electron microscopes give better
resolution than light microscopes...)
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>> No. Anyway sound goes through solid things as well as air so even if it
>> couldn't go through the gap it would go through the wall itself.
>
> OK... but presumably the velocity of sound inside a brick wall is
> different to free air, so there would be some kind of diffraction effect?
Probably, along with all the echo paths and different attenuation amounts of
different materials at different frequencies it probably explains why music
sounds horrible from the next room :-)
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scott wrote:
>>> No. Anyway sound goes through solid things as well as air so even if
>>> it couldn't go through the gap it would go through the wall itself.
>>
>> OK... but presumably the velocity of sound inside a brick wall is
>> different to free air, so there would be some kind of diffraction effect?
>
> Probably, along with all the echo paths and different attenuation
> amounts of different materials at different frequencies it probably
> explains why music sounds horrible from the next room :-)
It doesn't sound *that* bad. But there is a quite pronounced decrease in
bass as I walk through the doorway. You listen to the music and you
think the neighbors will be banking on the wall any minute now, and then
you step just outside the door and it suddenly seems radpically less
loud. I don't know if it's because you're out of line-of-sight with the
speakers or the width of the doorway or what...
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On Mon, 10 Aug 2009 10:57:59 +0100, Invisible <voi### [at] devnull> wrote:
>It doesn't sound *that* bad. But there is a quite pronounced decrease in
>bass as I walk through the doorway. You listen to the music and you
>think the neighbors will be banking on the wall any minute now, and then
>you step just outside the door and it suddenly seems radpically less
>loud. I don't know if it's because you're out of line-of-sight with the
>speakers or the width of the doorway or what...
Probably due to reasonable sound insulation of the walls and floor. I've lived
in flats where you would think that your neighbours were sitting in the same
room.
--
Regards
Stephen
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In article <4a744518@news.povray.org>,
Warp wrote:
[...]
> A sound wave (nor an electromagnetic wave for that matter) is not some
> kind of sine wave which goes through the air. The sine wave function you
> see drawn on a picture is just the representation of the function which
> tells which direction the wave is "pushing" at certain point (and how
> "strongly" it's "pusing"). The sine wave drawing is just a graph which maps
> time to amplitude ("strength" of the sound wave), it's in no way meant to
> represent the *physical* appearance of a sound wave.
>
> A sound wave is simply a phenomenon of air molecules pushing (and pulling)
> adjacent air molecules. The phenomenon traverses through air. The maximum
> strength at which this "pushing" happens is the amplitude of the wave, and
> the rate of change between "pushing" and "pulling" is the frequency. The
> distance between two "pushing" peaks is the wavelength.
Did you read one or more books that explain this and possibly more
with this level of clarity and language (more or less)? Could you cite
their names?
How come molecules "push" and "pull"? How come the strength varies?
I'd first think that it always gets weaker.
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> How come molecules "push" and "pull"? How come the strength varies?
The "push" and "pull" Warp is referring to (I guess) are the forces caused
by a pressure difference. This causes the next "bit" of air to be moved,
thus creating another pressure difference, and the next bit moved, etc, this
is how the wave propagates - it's the same as a longitudinal wave in a
slinky spring.
Of course at a molecular level "pressure" is caused by colliding molecules
etc, but I don't think you need to work at this level of detail to model how
sound waves propagate, you can just assume that each bit of air has a
pressure, and pressure differences will generate forces.
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