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.
Micronecta scholtzi
The male of this species produces its underwater courtship song by stridulating a ridge on its penis across corrugations on its abdomen. The area involved measures only 50 micrometres across, or about the thickness of a human hair. A team of biologists and sound engineers from France and Scotland have recorded "M. scholtzi" producing sound up to 99.2 decibels, a volume comparable to a passing freight train. The noise was so unexpectedly loud that the engineers checked the calibration of their instruments. It is classified by Guinness World Records as the loudest penis. Almost all volume is lost when sound moves from water to air, but even so remains audible to humans walking along the pond shore. This species is considered the loudest of all animals for its size. Despite knowing the mechanism of its sound production, researchers are still mystified by the volume produced and feel that once the process is understood, it could open up a useful avenue in ultrasonics.