Hi all,

I'm interested in determining the frequency response of small diameter tubing (~ 1 mm). To do this I have been producing pressure waves using an in-ear earphone. Unfortunately, this doesn't produce sufficient signal power at the low frequencies that I'm really interested in (0-50 Hz).

Does anyone know of any techniques that can be used to determine the frequency response of tubing at these low frequencies?

I was thinking of purchasing a small subwoofer speaker and coupling that down to the diameter of my tubing. However, I am concerned about the coupling down by such a large degree, and the speaker's ability to produce noise at these low frequencies. I was also thinking of using a pneumatic regulator, but this might not be able to characterize the tubes over the entire range (insufficient high-frequency power?).

I have already tried popping a balloon at the end of the tubing, however, this did not have sufficient frequency components to properly characterize the tubing sufficiently.

Any help that can be provided would be greatly appreciated.

Cheers,

Alistair