| From: | Stainless Steel Rat <ratinox@***.NEU.EDU> |
|---|---|
| Subject: | silencers |
| Date: | Mon, 31 Oct 1994 20:16:18 -0500 |
writes:
Adam> Why would the hardware need to be large? A gunshot releases less
Adam> than 1% of its energy as sound, so you certainly don't need the
Adam> energy storage of the shot.
You still need a fairly large and powerful emitter to generate a 110+dB
signal that retains the fidelity and nuances of the original signal. While
the basic waveform is simple, you're dealing with chaos theory with the
signal permutations: air pressure, density, humidity, temperature all
subtlely affect the waveform, adding all kinds of little nuances that need
to be duplicated to obtain full destructive cancelation.
[...]
Adam> Destructive cancellation does work,
Yes, it does. You can experience it by piping a "mono" signal through
"stereo" speakers. You'll find "dead spots" where the volume is
tremendously reduced or canceled entirely.
Adam> and would not emit a signal that could be detected, because most of
Adam> the signal will have cancelled with the original sound well below
Adam> ambient noise levels.
You can't detect it audibly, but there is still energy being emitted. Any
emitted energy can be detected somehow.
Adam> The geometry of noise cancellation for a gun is a simple cone
Adam> enclosing the bolt, breech and muzzle, not difficult at all. Also,
Adam> the platfor is relatively stationary, so Doppler effects become
Adam> relatively minor.
True.
Adam> The only real problem is cancelling the noise of the bullet, which
Adam> practically is impossible because you can't set up a speaker array
Adam> along the flight path of the round.
The same holds true for the propellant gasses escaping the barrel, which is
the cause of the "bang!" noise. For the same reasons you can't use
destructive cancelation to negate the sound of the bullet, you can't use it
to silence the gasses. That's where the sound suppressor comes in; by
reducing the velocity of the escaping gasses to subsonic, no sonic boom is
created.
Compared to the gas bang, the bullet is a quiet whip-crack at supersonic
velocities.
Adam> But the gun could be easily silenced, probably with hardware no more
Adam> bulky than a smartgun adaptor. In my game ASCI weighs .5 kg, as the
Adam> "computer" is a flake of diamond substrate with doped plastic epitaxy
Adam> and the "speaker" is an array of filaments with differing crystals
Adam> bonded to the surface.
If you mean to have this system negate the sound of the action, this is
sufficient (if this is correct, then I think I misinterpreted your original
comments). Added to a weapon that fires subsonic ammunition from a closed
bolt and has a good sound suppressor you'll have a weapon that makes about
as much noise as a longbow, maybe less.
Adam> Active radar cancellation would work in theory, except that the
Adam> velocities of the platforms (i.e. aircraft) are high so Doppler
Adam> effects become non-negligible, and the geometries are complex as
Adam> well. But, after all it works to a degree, as active radar
Adam> cancellation is also more well known as ECM.
Well, sort of. ECM is the most extreme form of destructive cancellation,
flooding the receptor with so much noise that it can't distinguish
anything. But as I said before, sure you could make an object "invisible,"
("The Minotaur" notwithstanding :) but because it's broadcasting a
signal/energy its presence can still be detected. Not it's location, but
definitely its presence. Kinda like a weird application of the Uncertanty
Principle: you can't see where it is, but you can determine where it's
going by tracking the energy emissions.
--
Rat <ratinox@***.neu.edu> |Do not use Happy Fun Ball on concrete.
http://www.ccs.neu.edu/home/ratinox|
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