Why are amplifier values posted at 1kHz?

[drgonzonm]

This is another one of the those nagging questions.  So its a standard, but why would someone want to make this frequency a standard?
It doesn't jive with the 400Hz speaker nominal resistance is quoted.  From page 4 of http://www.learnabout-electronics.org/Downloads/ac_theory_module07.pdf,
 For example, audio commonly uses a frequency of 1kHz as the standard for measuring impedance. This is because 1kHz is approximately
the centre of an audio amplifier ́s bandwidth, measured on a logarithmic scale

Where's Woody Allen, when we need him to make a movie about "Amplifiers and their Design" and questions not important enough to ask.   

[silverfox]

My guess would be: The system impedance may be optimal for testing at that frequency and that is how it originally got accepted. A good first look at system performance.


But significantly too:  We've always done it that way. The consumer recognizes that test as a gold standard and even though most do not understand the results. If it's not included in the spec sheet, the consumer will subconsciously prejudice the product. Can you image the situation when discussing the potential purchase amongst peers- What does it look like at 1 kHz? I don't know there wasn't any data on that- (falls down status ladder 3 rungs).

Probably manufactures' also don't know enough about the test- Particularly the sales department, so if it's not included or someone offers a different approach in a meeting, the new practice gets shot down with derogatory corporate speak encouraging the offerer to shut up until they are one of the chosen elite and smart enough to realize the meeting is not really about change or improvement but positioning towards the next layer up in the food chain.

Cost- A 1 kHz signal generator is less expensive than a spectrum analyser.

Silverfox.

[tubeswell]

... 1kHz is approximately the centre of an audio amplifier ́s bandwidth, measured on a logarithmic scale...

The load resistance of a speaker hooked up to an OT is something that shifts all over the place (within the elliptical load area on the plate characteristics graph) depending on a whole bunch of parameters including the OT impedance ratio, the amount of iron in the core, GFB in the circuit, and the speaker's resonance and excursion etc, which affect the speaker's impedance for any given frequency. 1kHz is a nominal handle for getting an idea of the approximate performance of the whole shifty thing