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.
Schiller Institute
In 1988, the institute initiated a campaign to establish "philosophical pitch" or "scientific pitch" as the classical music concert pitch standard. This tuning system is based on middle C set at 256 Hz, making concert A 430.539 Hz rather than the most commonly used 440 Hz. The Schiller Institute calls this system "Verdi tuning" because it was Italian composer Giuseppe Verdi who first sought to stop the increase in pitch to which orchestras are tuned. However, Verdi used the French standard 435 Hz in writing his "Requiem" in 1874; later he indicated that 432 Hz was slightly more optimal. It is this A=432 Hz standard that the Schiller Institute advocates, which does not align mathematically with their stated preference for C=256 Hz. French acoustic physicist Joseph Sauveur first researched then proposed the philosophical pitch standard in 1713, more than a century before Verdi began leading orchestras. Sauveur was strongly resisted by the musicians he was working with, and the proposed standard was not adopted.