The new rule is adopted from
https://www.ftc.gov/system/files/ftc_gov/pdf/p974222amplifierrulesnprm.pdf
(the previous supplementary discussion of 2023).
In brief, if you want to advertise the power of an amplifier in the USA, the test must be made in an ambient temperature of at least 77F, and must disclose:
measured output watts into an 8 ohm load
available at all frequencies from 20 to 20,000 Hz
with a maximum THD+N of 1% at any point from 250mW to the rated output
If the amplifier provides more than one channel of amplification, two channels (front left and front right if there is a choice of more) must be driven simultaneously to the same power and meet the same THD+N standard.
Amplifiers marketed specifically as "subwoofer" amplifiers are excluded.
Additional information may be disclosed, but the use of asterisks, small print and similar measures to obscure or disclaim actual performance is forbidden.
E.g. you can advertise that your amp can measure better than the standard,
but if so, the standard measurement must be disclosed.
The discussion states that tube amplifier manufacturers were responsible for the change from an initial proposal of 0.1% THD+N.
The FTC also clarifies that their intention was always to include noise in total harmonic distortion, but realizes that the two can be measured separately,
so the new requirement applies to the sum.
-dsr-
--
https://randomstring.org/~dsr/eula.html is hereby incorporated by reference.
there is no justice, there is just us.
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