acoustics

[supermode]

what is meant when you talk about difference in the spectra between the sources?
any geniuses out there? hanks

[kuhugaq]

it means they've been on the wacky.more in line with the electromagnetic spectrom than an acoustic guitar.soz if i'm on the wrong wavelengh lol

[jake-the-peg]

If you take a light source and split it into it's component parts with a spectrometer (which is a glorified prism although gratings can be used) you'll see the spectrum of colours.

If you examine it carefully you'll see dark bands in the spectrum. These dark bands correspond to materials in the light source absorping light at certain frequencies.

The bands can also be bright rather than dark depending on the set up.

Different materials have different 'fingerprints' of lines and you can work out what materials are in the sources.

The element Helium was actually first discoverred in the Sun using this technique (hence it's name) before it was discoverred on the earth.

So if you compare the spectra of your sources you can tell what is present.

If the source is heading away from you rapidly the bands will appear further down the spectra than they would if you were looking at a stationary source they would be 'red shifted' (blue shifted if they were heading towards you)

The bands will broaden more the hotter the source is.

So by comparing the spectra of two sources you cand determine a) what is present in them b) if they are moving relative to you or not. c) how hot the source is.

See here for more:
http://en.wikipedia.org/wiki/Spectral_line

[jake-the-peg]

Duh!

sorry just saw you titled it acoustics after all that.
If you take any signal you can break it down into a number of simple sine waves. This could be just a few sine waves like the 3 in this example:
http://www.science.org.au/nova/029/029img/wave 1.gif

Or it could be almost an infinite nummber - this is done using what is called a Fourier Transform

Try here for more
http://hyperphysics.phy-astr.gsu.edu/hbase/aud io/Fourier.html

[heathfield]

Oh Jake...! Put simply (!) - it's not easy to make sound equipment that will reproduce sound perfectly all the way from the very lowest frequencies to the very highest, (i.e., the sound spectrum). There will probably be one or more frequencies where there is a slight reduction in the quality of the sound. The frequencies at which the sound is less than perfect will differ between different makes of equipment. Hence the 'difference in the spectra between the sources'.