Build a Sound Outputter for Glass Shattering Frequency

[Zeteg]

Sound "outputter"

I really can't think of a better name than that right now. I'm to build a device that can output a very high frequency continuous sound messege, to an amplifer (like a guitar amp).

What's I'm trying to do, is have the frequency match that needed to crack/shatter glass.

Can anyone give me a general sense of what equipment I'd need, or what that sound wave should look like? Any information really would be of help, even prices for such materials :)

 

[Cliff_J]

All you'd need to do would be to match the output sound to the resonance of the glass. Its like rubbing a wet finger around the edge of a crystal glass and when you excite the resonance enough - crack!

A sine wave generator and a stereo amp (could be an old receiver you buy at a garage sale) with some piezo horns and some hearing protection would be about the list.

Search around, here was the second hit in google:
http://www.acoustics.salford.ac.uk/acoustics_world/glass/glass.htm

Cliff

EDIT: The frequency would be best to be spot on, the resonance of glass has a very high Q so the effective range of frequencies is quite narrow. You could just excite the glass with a finger (if you have a wine glass) and play back a recording. Guessing from the site I linked to above, the frequency of this glass would be around 350-400Hz and would require a pretty big horn to get the correct loudness at that frequency. So then a large high-efficiency prosound style driver would be a better choice.

 

[The Glom]

The frequency you need will be determined by the type of glass and by the shape of the glass. In other words, you'll need to find the resonant frequency.

If you're talking about a wine glass, gently tap the side with a pencil and listen for the ring tone of the glass.

If you record that ringing with a sound card, you might be able to sample a few clean waves from the first part of that ringing. Then you could play it back at high volume with the glass sitting in front of well-amplified speaker.

The trick is getting the speaker to produce a steady wave-train that exactly matches the glass resonant, reinforcing each wave without interference.

Good luck!

 

[GENIERE]

I’d add some feedback via a mike with a flat response. Provide a series of pulses. Each pulse would sweep a range of frequencies; say pulse 1 sweeps 100 to 200Hz, pulse 2 sweeps 200 to 300Hz…. Between each pulse allow a few seconds to elapse. The mike would respond to any resonate vibrations from the glass. If maximum feedback amplitude occurs in 200 to 300hz range. Pulse again sweeping at 200-210HZ, 210-220HZ…Repeat similarly until a small range of frequencies yields the maximal response. Increase output power to max and blast away.

 

[Zeteg]

Alright, thanks.

Any tips on how to record the resonance frequencies? I mean, once I record it, how would I find the frequency?

Oh, and how would I go about building a sine wave generator?

 

[Cliff_J]

Alright, thanks.

Any tips on how to record the resonance frequencies? I mean, once I record it, how would I find the frequency?

Oh, and how would I go about building a sine wave generator?

If you record it into a computer then you could take the file and process it with an FFT program to find the frequency distribution.

Some multimeters have a frequency counter built right into them, that would be even easier.

Search online and there are circuits for sine wave generators. You'll need to find the output frequency using the above to match it unless your pitch is really good. And you still need to find a speaker that can go loud enough to move the glass enough to break it!

Cliff

 

[Zeteg]

For a speaker, do you reckon that a guitar amp would work?

 

[Cliff_J]

LOL, maybe a half-stack at short range.

What kind of glass are you trying to break? If its a crystal wine glass then if you could encase it inside the proper tube then you could really increase the effective SPL a speaker can produce. Otherwise sound propagates sphereically and loses quickly, confining the propagation (controlling the directivity) will maximize the energy delivered. Note in the link above they used a 10" speaker on the end of their tube and did not have success with perfect glasses, only when an imperfection was introduced were they successful.

If you're trying to recreate the scene in the movie "Singles" where the car windows blow out then it would be easier to remake the windows from plastic like http://smooth-on.com/plastics.asp#smash and shatter them with a charge or firecracker.

Cliff

 

[Arctic Fox]

Alright, thanks.

Any tips on how to record the resonance frequencies? I mean, once I record it, how would I find the frequency?

Oh, and how would I go about building a sine wave generator?

“Create tones using a computer with a sound card. It can create selected waveforms including sine, square, triangle, sawtooth, impulse and white noise at selected frequencies between 1 to 20,000Hz. The software could be used as a substitute for the traditional electronic tone generators in Radio Stations or Audio Studios.”

Site: http://www.nch.com.au/tonegen/index.html
Download Tone Generator: http://www.nch.com.au/action/tnsetup.exe (free!)
I use this programme to find the resonant frequency of my apartment! ~44.5Hz :D


Note: I personally would not use a 10" subwoofer for 350-400hz. Find a speaker/horn with a peak at the frequency you want to hit at.

Also, if you can find something to measure the frequency of sound, check the glass by tapping it with a metal spoon - this will give out its resonating frequency; sweep the sound across that +/-20hz. Or you can try it 'by ear'...

 

[Zeteg]

Oh, thanks. Umm, any idea on how to build one..?

 

[Arctic Fox]

Build one what?

Frequency Generator, speakers, wine glass?

Sure.

 

[Integral]

If you can find and produce the resonant frequency, you should not need a large amplitude sound source. That is the whole idea of a resonance. Geniere mentioned the concept of feedback, I do not think that a microphone would be best for that, better would be something like a piezoelectric sensor on the object you wish to break. This would translate mechanical vibrations into an electric signal which could then be used to determine the driving frequency. Again if you set it up correctly you should not need and indeed do not want a high volume signal. If you overdrive your speaker, you will induce noise which could well disturb your resonance. You should be able to induce the resonance with a very low volume at the correct frequency, what will be critical is the ability to produce a pure tone.
Do not experiment with this anywhere near my home!

Good luck

 

[Cliff_J]

Integral I'd beg to differ on opinion as to the volume level needed to break the glass. Glass seems to be quite resilient and fairly well damped. It would seem simple enough to introduce enough physical displacement as to exceed the strength. But here's my thoughts - if constructed consistently all parts would vibrate in-phase creating only compressive and tensile loads. Getting some sections to vibrate out of phase to help build up shear forces instead of just tensile forces should help a lot. That should be as easy as the first harmonic, but that could be well damped too.

As stated in the page I linked to above, an imperfection made breakage very easy in a system where a perfect glass would not shatter. When I was young some friends and I purposely tried to break wine glasses by setting multiple glasses next to one and excite the resonances with wetted fingers. It got loud but nothing broke and this was crystal glass as far as I know. Oh to be young again, but we thought for sure we've have big time destruction.

Oh, and no I wouldn't use a 10" subwoofer, I'd use a 15" or 18" prosound driver with a very high sesitivity and low inductance voice coil if I wanted 400Hz and really loud. You might be able to construct a horn but if used in a confined space then its likely to not work.

According to the following link, a level as low as 92-94db would be sufficient. Any guitar speaker worth a salt should be able to muster that! Validity is unknown but an interesting thought experiment nonetheless.
http://www.straightdope.com/classics/a3_333.html

Oh, and now we can include the Millenium bridge in addition to the dramatic collapse of the Tacoma Narrows for examples of amplified resonance. The following link has an explanation and graphs of excitation force versus damping if you click on the numbers 1-5 in the middle of the page.
http://www.arup.com/MillenniumBridge/challenge/oscillation.html

And then this page for the "magic" moment when the lines cross:
http://www.arup.com/MillenniumBridge/challenge/results.html

Cliff

 

[Arctic Fox]

400Hz just doesn’t 'sound' right for the resonance frequency of glass...

I’m willing to guess (without a tone generator in hand) it would be upwards of 1000-3000Hz. And once you hit its note, you shouldn’t need a lot volume.

You could probably shake apart plate-glass at 15-30Hz, but the resonating frequency would be a lot higher.

A neat trick is to have a subwoofer in a room, set at a reasonable volume. Sweep through the frequencies from 10 on up. You’ll notice when you hit the resonating frequency of the room itself when the volume seems to get a lot louder at that frequency (and the walls start to vibrate).

 

[Cliff_J]

With the subwoofer you're exciting a room mode. And actually a room with parallel walls will have three unless two or more of the three dimensions for height, width, depth overlap. Most subs are placed near where two boundries (floor and wall) meet and this increases the effect because of two modes are available, or a corner where three boundries (floor and two walls meet) which means that now three modes are easily accesible.

We're all guessing here and the orignal poster hasn't stated his intentions. Based on the one website I found with their empircial data and assuming their FFT analysis is accurate enough and 350-400Hz should be a decent starting point. The thread starter could simply sweep the frequency range with a crystal glass under test in front of his guitar amp and feel which one excited it the most with his finger!

If you've done the frequency sweeps with your sub you know its pretty obvious when you hit the resonance of the heating registers and all the other items around the room. Far better example of the effect than mode excitation.

And guessing from the thread starter's absence he might have been discouraged that he cannot create a glass busting weapon that could move around and shatter glass at will. And since most glass is 'soft' glass then the idea of resonance falls well short of just creating large pressure disturbances to physically shatter the glass. Good luck with that and the power needed to do it, better just grab a big rock.

Cliff

 

[tom12519]

Try 22.275 Hz whilst you're at it.