messier88

I see. That's not exactly what I was expecting. Does anyone know of any sources for this sort of data on different materials? I'd love to see some frequency/speed graphs. How about this idea of waves travelling along an object reaching the end and bouncing back? I'm imagining this happens as the energy has nowhere to dissipate. Thanks so much for your replies so far.

Well that makes some sense. I guess it's something to do with the properties of solids that allow this to happen, and I think that ice and metal (from the examples I gave) have similar resonant frequencies. What has me confused is this thing of some frequencies seeming to travel faster than others... is this just an illusion? One of the factors in both of the examples is that the sound has travelled a distance, so is it that if a solid receives an impact the energy propagates around impact and travels further at it's resonant frequency. When received over a distance the effect is multiplied enough that those frequencies arrive first and in the case of something like metal they are the higher ones?

Ok, so this needs a bit of explaining. I'm a very amateur scientist... well actually I'm really a sound designer, that is amongst other things I create sound effects. I'm also naturally quite curious and like to ask the question why? as I'm sure do you. So my interest in this topic stems from some sound effects, namely the very famous star wars laser sound created by Ben Burtt which was a recording of himself hammering a steel guy wire. As I understand it the phenomenon of acoustic dispersion is responsible for the high frequencies in the sound moving faster than the low frequencies. Other examples of this sound are this great recording under ice sheets: http://silentlistening.wordpress.com/2008/05/09/dispersion-of-sound-waves-in-ice-sheets/ So I'm wondering why this happens in some materials and not others, and really why it happens at all. As I mentioned, I'm not a scientist so layman's terms would be appreciated! Many thanks, Mark