Test Equipment vs The Ear

It was Harman Kardon back in the 70's who was touting the audible effects of inaudible frequencies. They claimed that their ultra wide-band receivers, preamps, and amps (4Hz to 140kHz) would outperform the competitor products (typically 20Hz to 20,000kHz) even though they were outside the range of human hearing. They didn't compare a competitor's product against their unit, rather they built (2) identical units and limited the bandwidth on one to the 20-20 range. Supposedly over 80% of the professionals they played them for identified the wider bandwidth as more musical.  Harman Kardon's explanation was that inaudible frequencies produce harmonics in the audible range.