Hi,
I didn't know 5-string electric basses existed; interesting. All the ones I've seen have four strings. Kind of similar to the Bosendorfer Imperial Grand piano, which adds extra keys in the lower bass (all black, to differentiate them), the lowest of which has a fundamental around 16 Hz.
The bottom key on a conventional grand piano is at 28 Hz.
The Bosendorfer Imperial is seldom used in concert or on recordings and the extra bass keys are seldom played. I have only one recording on which the Bosendorfer's extra bass notes are used. They are impressive.
Regards,
Alan
