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.
Adam Lopez
According to the "Guinness Book of World Records", Lopez held the world record for highest vocal note produced by a male from 2008 to 2018. That pitch is designated D in note-octave notation; it is three semitones above the highest note on a standard grand piano or 4435 Hz. Before achieving this record, Lopez held the previous Guinness World Record for singing a C in 2005. On January 20, 2018, the record was surpassed by Xiao Lung Wang from China recognised by Guinness World Record for singing E8 or 5,243 Hz.