No, the regs don't require that the manufacturers test at any specific frequency or range of frequencies, but the frequency has to be specifically stated in conjunction with the power number. Typically the 20Hz-20KHz range is used for the testing and the published specs, with a 1KHz number(typically 5-10% higher)sometimes listed as a supplementary figure, or as the basic rating for some less expensive units.
For example, I'll quote the spec for a receiver that cost $151 delivered as a factory refurb: "75 watts minimum continuous power per channel, 8 ohm loads, 2 channels driven from 20Hz to 20 kHz, with a maximum total harmonic distortion of 0.08%. 100 watts minimum continuous power per channel, 6 ohm loads, 2 channels driven at 1 kHz, with a maximum total harmonic distortion of 0.1%" These are the specs from the measurements pursuant to the FTC regs(at least 5 continuous minutes at the full rated power). Additional numbers(higher)follow, under standards suggested by industry groups in various countries.
