Hi,
I'm new to acoustics in general but I have this instrument which
involves lightly scraping the end of aluminum pipes off porcelain
glazed tiles (a sort of glassy surface). One tile is on the ground and
the other is lifted slightly off the ground for a different timre. I
put a video up to show it :
http://www.youtube.com/watch?v=-LP62rnCNAk
I have to be able to explain why this sounds the way it does for my
acoustics class, while you can see from the video that the sound of
the pipes ring through and is roughly the same pitch and timbre as
when the pipes are struck normally (like with a mallet). This sound
should be easy to explain (the pipes resonate to a frequency whose
wavelength is double the pipe's length) but how do I explain the
overtones that are brought out by the scraping? How do I explain the
actual scraping sound and the role the tiles material and size plays
in this?
Obviously friction is setting it in motion to resonate but the more
unusual sounds this produces seem harder to explain. The sound of
scraping materials (friction) seems to be undiscussed in my acoustics
book.
If you could point me to resources (websites or books) that could help
me or answer this directly I would be so grateful.