here is the link :
http://intellagence.eu.com/acoustics2008/acoustics2008/cd1/data/articles/003579.pdf
i know how to run an impedance test but HOW A PIEZO can generate a 20hz tone ?
I have been up to make an impedance tube to measure acoustic Z and calculate absorption coefficient of materials . and having a sound generator(speaker driver) in it usually gives you near 60 hz response so your data will be charted starting 60hz and above.
My goal is to measure from 20hz...