QLD
546 posts
Hi i was playing around with a wine glass in my dishes the other night and i got it to vibrate and sing by rubbing along the rim does anyone know y this happens.
NSW
4521 posts
The glass has a resonant frequency. This is the frequency that the glass likes to 'vibrate' at. (This is the same as a swing or pendulum having a set frequency that it will swing at.)
When you run your finger around the damp rim of the glass, your finger is actually gripping then slipping on the wet surface of the glass rim. You will notice that you have to apply just the right amount of pressure and speed to make it work. This is when your finger is gripping then slipping at the resonant frequency of the glass causing it to vibrate more and more until it emits a tone loud enough to hear. (This is the same as giving a swing a little push and each time it swings higher and higher.)
Regards,
Harrow.
QLD
340 posts
it's because there's a glass and a half of full cream dairy milk in every 200 gram block
QLD
69 posts
try to get a look at the mythbusters edition when a singer smashes a wine glass with amped voice
WA
877 posts
we tried to smash a wine glass at school (like 5 or 6 years ago) with a massive amplifier and a computer which produced exact sounds. Was great fun, we measured the resonating frequency of the glass by running our fingures round the rim. then found that frequency and played it back through the massive amplifier. Got it going real loud. Only problem was it wasnt a real good amp, and when we increased the volume the frequency changed ever so slightly. We could get the class resonating at low volumes, but when we tried to ark up the volume to break it, it would change the frequency and the resonance would stop. Everyone around the school could hear us though, so we didnt care all that much, was good to be distruptive.
WA
6277 posts
Hey Filthy,
I don't think that an amplifier can change the frequency of the signal. Distortion yes, frequency no. Perhaps it was introducing harmonics? Did you do a frequency sweep (over say 20 Hz, centered around what you thought the resonant frequency was)? Perhaps the phase was wrong, so did you move the speaker back and forth to try to get the right phase? Did you try pointing the speaker DOWN at the glass, or only from the side?
The biggest problem with trying to make something resonate well is that you need some form of feedback loop. When most people try to make things resonate they hit it, figure out the frequency, then try to reproduce that frequency without feedback, which almost never works.
Take the mythbusters episode where they tried to make a bridge fall apart... that time there was no feedback, even if they had tried to figure out the resonant frequency beforehand (which they didn't!). They should have put a position sensor on the bridge, and fed that back to the boots. The feedback mechanism with real soldiers on bridges is their sense of balance, as in, they are actually on the bridge.
There are lots of examples in nature of resonance, the one most people are familiar with is a playground swing. If you push the swing at one end of its travel then you rapidly get oscillation. If you push it at the wrong end of its travel (even though you're at the right frequency) then you damp it down completely and it stops swinging. So you really need to get the phase right. If you have no feedback, and your frequency is slightly out, then it will be like you're pushing in the right place part of the time, and the wrong place the rest of the time... so the net result is that it doesn't resonate well.
If you really wanted to make a wineglass smash using sound then the easiest way would be to put a small microphone on the glass, and feed that signal back into the amplifier. This means that you'd always have the right frequency. You could move the speaker back and forth to get the phase right. I don't think that you would have to have the system all that loud to make it smash.
When rubbing a finger on a glass the feedback mechanism is the interface between the wet glass and the finger. Violins work exactly the same way, with a stick/slip cycle between the bow and the string.
Oh look I've posted a novel again...
NSW
762 posts
The easiest way I have found to smash a wine glass is to drink about a dozen glasses of wine and eventually that wine glass will fall out of your hand and smash. Then and only then, you can start singing.
The above works best at friends weddings.
QLD
340 posts
Sandiman - u going to wello?
QLD
14968 posts
hi filthy,
i think the problem with the amp changing frequency was actually due to the reverb within the room space. so the amp had the same frequency but what you heard began to change due to cancellation, standing waves etc.
an example of this is a stereo with bass boost. play something at a soft volume and you need to boost the bass.
give it heaps of volume and you need to cut some of the bass. guitar amps work the same. when you get the amp eq setup for live playing, you should do it at the volume at which you normally play live.
a couple of other issues could be that you were useing a solid state amp. they are no good at high volume, they clip and sound crap because they can't preduce the full signal. a tube amp introduces natural distortion as the curve peaks and keeps the tone/freq smooth..
you would also find that a cheap ass amp, for example a behringer... will have a cheap ass speaker with a poor timbre. at higher volumes the speakers start to give out which means they can't produce the frequency you're after. a superb speaker such as a celestion vintage 30 will preduce better timbre and can handle 11 on ye old marshall or hughes and kettner or orange or vox....
umm, have i been possessed by leeD..[}:)]
come on lee, tell us what you think... add another feather to your cap.
