Resonance and dB

[Marks256]

Ok, i have the odd itch to break glass with sound. I have a glass cup, and found that it resonates at about 1624hz(i can't remember exactally). I need to know how loud i need to play the frequency to break the glass.

Also, what is a dB(decibal). I know it is volume, or how much air is being moved, but exactally how loud is 1dB?

If you would like, i will draw a diagram of how i plan to go about this, too.

 

[Nigel Goodwin]

Ok, i have the odd itch to break glass with sound. I have a glass cup, and found that it resonates at about 1624hz(i can't remember exactally). I need to know how loud i need to play the frequency to break the glass.

Have you never watched Myth Busters?, they did it on there - it's NOT simple to do, and it requires considerable power - they also only managed to do it with specific susceptible glasses - a glass 'cup' doesn't sound very likely!.

Also, what is a dB(decibal). I know it is volume, or how much air is being moved, but exactally how loud is 1dB?

No, dB is simply a ratio, either of voltage or power, it's meaningless unless you specify the reference point it's related to.

 

[Hero999]

I thought that the breaking glass with sound thing was a myth. To break that glass you'd need a deafiningly lound sound. I don't know if you could buy a speaker loud enough.

Anyway I would do it by connecting a small piezo transducer to the glass ad connecting it to the mic input of a large audio amp with a huge horn speeker on the output. The feedback should be at the resonant frequency of the glass and if it vibrates enough it will break.

 

[dknguyen]

No, dB is simply a ratio, either of voltage or power, it's meaningless unless you specify the reference point it's related to.

Usually referred to the threshold of human hearing for sounds.

 

[Hero999]

https://en.wikipedia.org/wiki/Decibel

 

[Marks256]

Yes, Nigel, i have seen the episode. In my opinion, it looked fairly easy. I have software equivalent to the software that guy was using. I love it! The bad thing about it, is that is shareware. $49us to be exact.

If a cup don't work, then i will just pick up some cheap wine cups from a discount store(we have PLENTY of them in this neck of the woods. )

Anyways, i have a setup similar to what they had on Myth busters. Please use your imagination with this drawing

**broken link removed**


All i need to know is what should i use as an amp? Does anyone have some SIMPLE Schematics? I guess if all else fails, i do have a 400watt Stereo amplifier that needs minor repairs(replace a transistor).

 

[audioguru]

I doubt that you have a speaker that can handle 400W continuously.
Your speaker and your ears will break long before the glass breaks. The amplifier might also break.
I think an expensive leaded crystal glass resonates better than a cheap glass one.

 

[Dr.EM]

I remember a science video we were shown at school where this experiment was conducted. They used a powerful horn speaker; with it and the glass in a soundproof room. They played the resonant frequency at levels "higher than a jet plane taking off" and the glass did not break. It did, however, turn to jelly! It wobbled around like it was completely melted and instantly "solidified" when the tone was removed. Quite fascinating, probably a more interesting result if you can achieve that, but it wouldn't be easy.

 

[Marks256]

I doubt that you have a speaker that can handle 400W continuously.

You are 100% correct. I don't have a single speaker that can handle 400W continuously, but i do havespeakers that can handle 400W continuously.

Your speaker and your ears will break long before the glass breaks.

Nope. Plenty of ear protection! Seriously. I had thought of this before i even got the idea of trying it myself. I have a nice pair of headphone earplug things that REALLY knock out A LOT of sound.

The amplifier might also break.

This is true. I am not sure what i would do if it would break? I am not sure if i will be able to fix it in the first place.

I think an expensive leaded crystal glass resonates better than a cheap glass one.

You are probably right. I will probably head to walmart, or something, and get some nice glass ware, and some cheap glass ware.

EVIL THOUGHT: Or, i could just "borrow some of my mom's nice crystal ware.... Just kidding

 

[audioguru]

How are you going to connect more than one speaker per channel to an amplifier? Maybe just two 8 ohm speakers which is a 4 ohm load when in parallel. Your amplifier probably cannot drive a load with an impedance lower than only 4 ohms so additional speakers in parallel will just blow up the amplifier, like now.

 

[Marks256]

The AMP is a car AMP. You know, the ones that have about six to eight speakers connected at a time. Yeah, thoes are the ones.

it looks something like this;
**broken link removed**

Not totally, but close.

 

[audioguru]

The speakers in your car won't all have the same phase at 1624Hz. Some will be in phase and others will be out of phase.
Only if the speakers are exactly the same type, are away from reflective surfaces, and are at exactly the same distance from the glass will they be in phase so that their sound levels add.

 

[Marks256]

You are trying to make this difficult, aren't you?

 

[audioguru]

It is difficult to break a glass with sound from loudspeakers.
Do the math:
1) Your speakers probably produce a sound pressure of 90dB at 1m with 1W of power.
2) You have 8 speakers and a total of 8W making a sound pressure of 99dB.
3) 400W will make a sound pressure of about 117dB but you need at least 140dB.
4) To reach a sound pressure of 140dB you need a power into your inefficient speakers of about 87,000W!
If your speakers are very efficient at 96dB/m/W, then you need a power of only 21,750W!

 

[Marks256]

Do you have a better idea?

 

[audioguru]

Do you have a better idea?

Sure, a hammer will break a glass pretty well.

 

[Marks256]

He he. Lol.

I will be happy if i can at least make a glass wiggle a little with sound.

I was just doing some research on the net. I found that the sound levels need to be about 140dB, just as you said. I think am positive i have speakers that are big enough, tough. I think that are at my grandparent's home? I am not sure. How big do you think the speaker(s) should be? What about impedance?

 

[audioguru]

An expensive 60W PA compression driver in a pretty big cast horn makes 132dB at full power. Five would make 140dB at 1624Hz. They don't produce bass.

Big cone speakers aren't sensitive enough to produce such a high sound pressure, instead they produce bass pretty well.

 

[hjames]

I wonder if you can just get an ultrasonic cleaner (or parts for one) and misuse the piezo element.

 

[Nigel Goodwin]

I wonder if you can just get an ultrasonic cleaner (or parts for one) and misuse the piezo element.

Far too high a frequency, you're looking for mid-range audio.