@guscreek Interesting question.
Hence, in my opinion the double bass is a more reliable reference of the bass than piano considering the how often one can hear these lower notes. One can clearly hear the purring of the double bass in jazz ensembles most of the time right in the middle of the sound stage. It would be interesting to hear from those who know how often one hear the lowest note of the modern piano (27.5 Hz) in classical and jazz music.
@toddalin Terrific answer. Do you play?