Thanks for all the replies and help offers.

I am located in europe so there is no dropping by. I have a tone generator and a low impedance amp. I guess that should suffice for an audible inspection. If i dont forget i will also try with reversed connection.

First i am going to remove the phragms and clean the gap.

The only thing i lack for measuring is a measurement grade mic amp. I've been looking at the little behringer which has a 'flat' setting. I wondered if the ecm8000 measurement mic with phantom supply plugs into my pc mic-in, any idea if this will work?

Thanks again, Coen