Does anybody know how many khz it takes to break glass?

Answer 1

Sound being a wave travelling, which is an oscillation of pressure. When the high-pitched sound and the glass resonate, it causes the glass to vibrate. Depending on the glass structure and the note emitted, if you keep the frequency of the note at high volume long enough, the pressure on the glass eventually can make it vibrate into pieces.

Answer 2

Since glass is a crystal, there are frequencies that will break glass. Moreover, the amplitude of the sound isn't particularly important: At the resonance frequency of the glass, (which is the only frequency that's going to shatter it,) the waves add up and will make the glass shatter even with a relatively low amplitude, (not very loud.)

However, determining the resonance frequency of "glass" in general is quite impossible, and in a specific case of a certain chunk of glass is extremely difficult. That is because the resonance frequency depends upon several different factors.

The size of the piece of glass
The shape of the piece of glass
The composition of the piece of glass
The temperature of the piece of glass
The crystal structure of the piece of glass (tempered or not)

The atmospheric pressure
The atmospheric temperature
The mounting of the glass (like a window? sitting on the ground?)

There are probably other variables I've forgotten about as well. PLUS it's not a simple problem even if you know all those things: It's a 3-dimensional mass-spring-damper equation that's fiendishly difficult to solve, and will have multiple solutions even whe you do, (meaning there are actually several resonance frequencies.)

It's far far simpler to take a sine wave generator, (which is to say, a speaker,) and simply cycle through the frequencies until the glass shatters, but keep in mind: For a sufficiently _thick_ piece of glass, (i.e. not a window pane or crystal stemware,) even the resonance frequency is going to lack the ability to shatter the glass.

Sorry to disappoint you, but picking a material (glass) and a frequency (in KHz) is simply not enough to determine the frequency that'll shatter it.

Answer 3

If you're talking about a crystal wine glass, the classical example, just tap the rim of the glass and use whatever frequency it naturally rings at. You can use a microphone and frequency counter to measure, or just tune it by ear.

Answer 4

There is no set frequency. It will only work with crystal and requires the sound to be at a sufficient amplitude and it needs to be at the frequency the crystal resonates at.

Answer 5

To break crystal glass, it's C sharp which is less than 1KHZ at about 140dB.
http://www.tonalsoft.com/enc/k/khz.aspx
http://www.physics.ucla.edu/demoweb/demomanual/acoustics/effects_of_sound/breaking_glass_with_sound.html

For other glass, it depends on the glass, just crank the dB up until it breaks.