Strange aural stuff...

[Visirale]

When I strike an open note on my electric bass the corresponding note on my double bass sounds, and it resonates. Since my double bass still hasn't been set up this is quite a nuisance... Last night I was in drop C on my electric for kicks, and I cranked up my amp, and I let the C go, and the G string on my double bass was going crazy. It was literally flapping back and forth over the area of about an inch...

I'm curious as to why this happens... just a chance to educate myself on acoustics or something...

So why does this happen?

 

[Ben Jammin']

Different materials have different natural resonance. If ur double bass' G-string has a natural resonance of C (which is a little odd) it'll go crazy when ever the note C is played near it. The sound wave will be in sync with the wave the string produces (and it is a wave, just a very fast one)
This also explains why different things around a room ring on certain notes, and why if u stand really close to a big amp and play an open string the note should theoretically ring for ever.

 

[Stubb]

It's resonating because G is the 5th of C- the frequencies interact in some way. I think.