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Notes
At AMR we feel that the IHF standard represents the best available rigidly mandated and standardised, musically relevant measurements
applicable today (in preference to DIN45500 among others) despite their formidable age and our wish for something more up-to-date, while
the FTC mandated standard is applicable under like-for-like ‘fair trade descriptions’ requirements in the USA (but we feel what is fair in the USA
is still fair elsewhere) to make sure that one maker’s advertised ‘watt’ is like-for-like equal to that of another. As a result we feature IHF-based
specifications and measurements where possible and FTC where mandated/appropriate.
i. FTC: Federal Trade Commission (USA)
Federal Trade Commission: a US-based trade standard body whose standardised measurement procedures (2000 revision) we apply where we
would be required to do so under US Law, even though we are UK-based. Past the FTC ruling (originally from 1974, updated in 2003) derived
rating there is a secondary power rating, the IHF ‘Dynamic Power’ (also defined in the mid 70’s) which is the maximum power the amplifier
can put out for a burst 20ms long, or in other words for a short musical peak. An amplifier that can deliver 200W for 20ms but 50W
continuously will have a FTC Power Rating of 50W but an IHF Dynamic Power Rating of 200W. An amplifier that can deliver 200W for 2ms
but 150W continuously will have a FTC Power Rating of 150W but an IHF Dynamic Power Rating of 200W. However, the available
undistorted peak output with music signals is actually the same for both Amplifiers.
ii. IHF: Institute of High Fidelity
Institute of High Fidelity: a US-based standard body (now incorporated into the International Electrotechnical Commission) whose standardised
measurements we usually apply. The Federal Trade Commission defines the information about an amplifier that a US manufacturer (or
distributor) must provide. FTC ratings derive from test data, and state an amplifier’s continuous average output capability into a defined load
across a defined frequency range (usually 20Hz - 20kHz, but any range can be used as long as it is stated). Also, the amplifier is tested with ‘both
channels driven’ (placing maximum strain on the power supply), so the test demonstrates its capacity in real-world conditions. This allows like-
for-like comparison of amplifiers that use FTC ratings. For that reason, you won’t find any published FTC ratings for an amplifier’s output into
a 2 Ohm load.
Abbingdon Music Research is a subsidiary of the Abbingdon Global Group
22 Notting Hill Gate; London; W11 3JE; United Kingdom;
Tel: +44 (0) 870 420 5505; Fax: +44 (0) 700 596 1065