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Sonic grenade

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LAN_403

bluecommander

Sat Feb 16 2008, 04:01AM

Registered Member #1278 Joined: Thu Jan 31 2008, 10:34PM
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Posts: 2

Yeah, I heard that about the spy device, and saw an ad in the back of my Popular Science magazine for one. The question is, How well does one work? I think that playing with sound is cool, and I do like a challenge

. This would be neat, but even I don't see a purpose. I do remember a random sci-fi movie where a guy with a revolver sized weapon was knocking over people with sound waves. Such a thing would be possible about the time coil guns become practical

. Anyway, Iknew it was theroically possible, and I knew it wasn't going to be practical, but I just thought of the subject as a neat one

Shaun

Sat Feb 16 2008, 04:38AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Its known as a laser listener, and there are amateurs who have built them. Even one right here on 4HV:

Chris Russell

Sat Feb 16 2008, 08:00AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

Mates wrote ...

I wouldnâ€™t be so resolute that destroying glass without flaw by sound is not possible. Resonant transfer of energy has no real limits. The limiting factor is the power of the source and how good is the resonance. Theoretically you can deliver enough energy to the glass not only to break it but also to melt it.

And just how high is the Q of a window pane, or a regular drinking glass? How about one heated enough to be slightly soft? The amount of sound energy required to melt a drinking glass into a puddle would be so laughably high that you might as well have just set off a nuclear bomb instead. I would be very, very surprised if it were possible to break even a flawed wine glass with a regular high power speaker and a few kilowatts of sound at five feet. The idea that one can shatter any piece of glass just by hitting the right note is simply a fantasy.

The sonic grenade idea suffers the same basic problem -- you can't really break glass with sound unless it has a very high Q and you are right next to it, or your power levels are impossibly high. While you could probably theoretically build something that you could toss through a window and have it land next to a wine glass, at which point it emits enough sound to break the wine glass... you'd have saved yourself a lot of time and effort by just tossing a brick in the window and hitting the glass.

Backyard Skunkworks

Sat Feb 16 2008, 09:25PM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

When mythbusters broke their wine glasses it was at very close range and high amplitude, it also took several dozen glasses before they found one that the lead singer of Nitro could break un-amplified. I think destroying stuff with sound is totally doable with some resonating Unobtainium.

HV Enthusiast

Sun Feb 17 2008, 03:57PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Breaking the "classic" wine glass is more resonant action then input amplitude.

First, its not glass that is breaking, its CRYSTAL. Glass has a very low Q, while crystal has a very high Q and a distinct resonant frequency.

The important thing here is that the voice has to be the resonant frequency of the crystal glass. You can easily find the resonant frequency of a crystal glass by rubbing your figure along the rim of the glass and measuring what that frequency is.

Ella Fitzgerald just didn't sing and the glass broke, she tuned her voice to the exact resonant frequency of the crystal glass. And as others have said, the glass may have been specially made for the purpose.

Chris

Sun Feb 17 2008, 07:26PM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
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All wine glasses are made of glass, an amorphous solid composed primarily of silica. That includes "crystal" glasses which are actually just a type of GLASS. There is nothing crystalline about them. I would be impressed if you found a wine glass made of actual crystal. Any drinking glass will have a resonant frequency; it is not something unique to ones made of leaded glass.

Marko

Sun Feb 17 2008, 08:35PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

You guys are starting to make this appear like something paranormal :p

First, its not glass that is breaking, its CRYSTAL. Glass has a very low Q, while crystal has a very high Q and a distinct resonant frequency.

Yes, how do you mean this? As chris says, 'crystal' glasses aren't really crystal.

From what I know the Q of a glass is primarily defined by it's shape; the long narrow neck separates the ''resonator'' from ground and slows down energy loss many times to what you would have with a drinking glass.

The other very important thing is that sound is focused as much as possible; if pressure on flanks of the glass is equal to pressure on front it will cancel out and there will be no significant vibration.

That's why it is possible to break the glass with a holed cover over the speaker or by keeping it close to mouth but much harder at some significant distance.

HV Enthusiast

Mon Feb 18 2008, 02:47AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Chris wrote ...

All wine glasses are made of glass, an amorphous solid composed primarily of silica. That includes "crystal" glasses which are actually just a type of GLASS. There is nothing crystalline about them. I would be impressed if you found a wine glass made of actual crystal. Any drinking glass will have a resonant frequency; it is not something unique to ones made of leaded glass.

You know what I meant. No need to argue semantics. In the industry (which we were discussing), there el cheap drinking glasses made from "glass" and fine drinking glasses made from "crystal." I figured we were all smart enough here to realize the difference and that "crystal" is merely an industry term.
And yes, any drinking glass will have a resonant frequency, but those made with "lead crystal" have significant higher Q's than your typical el cheapo Walmart glass due to the properties of the glass.

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