Did some research about recording double basses using piezo-pickups recently. It’s always nice to have one track of acoustic bass totally clean and leakage free, just in case. We all know the problem though: nosy, bass-less sounds, almost useless in the end. Solution?
Piezo-electronic pickup systems used for acoustic double basses and other acoustic instruments feature extremely high impedances, typically higher than 1 MΩ (Mega-Ohm). In studio and live environments the connections usually will be made using DI-boxes. Those work well together with magnetic pickups we find in electric guitars and bass-guitars, that have impedances around 1 MΩ and lower. But if we connect a piezo-PU with it’s extremely high impedance to an input with a lower impedance, we run into problems. To put it short, the sound of the PU will interfere with its own out of phase copy, mirrored by the input. The result is the apparently typical piezo-sound we seem to know.
But if we use an input with the same impedance of the piezo-system or higher theses interferences go away almost totally. The result is a well balanced bass-sound with rich low and high frequencies and no high-mid-scoop. Still an electric sound, but highly usable together with one or two mic-tracks.