Harman Kardon
In 1959, Harman Kardon marketed the Citation II, an early ultra wideband stereophonic tube amplifier. Designed by Stewart Hegeman, it featured 60 watts/channel output with a frequency response of 18-60,000 Hz at 20 watt output. The company promoted their philosophy of designing high fidelity sound using amplifiers that provided widest possible audio bandwidth. Although the human ear highest audible range is around 20,000 Hz, the full range of sound goes beyond that with harmonics and overtones that may be beyond the hearing range of the human ear. These harmonics interact with other frequencies to produce audible secondary sounds or interference. Harman Kardon promoted the design in audio magazines and product brochures.
Hyperbass flute
The hyperbass flute is an extremely rare and the largest and lowest pitched instrument in the flute family, with tubing reaching over in length. It is pitched in C, four octaves below the concert flute (three octaves below the bass flute, two octaves below the contrabass flute, and one octave below the double contrabass flute), with its lowest note being C, one octave below the lowest C on a standard piano. At 16 hertz, this is below what is generally considered the range of human hearing (20 to 20,000 Hz).