Speaker's harmonics - against what?

[anli]

Good speaker's datasheets, along with frequency response, supply
distortions (mostly second and third harmonics) curves. Does anybody
know how does "zero level" for these curves is defined? I see two
opportunities:

- "zero db" level is sensitivity at the same frequency,
- it is some kind of "normalized" level, which doesn't depend
on frequency (for example, from main speaker's parameters table).

Are there any official recomendations? Is there de-facto standard?

[catapult]

- "zero db" level is sensitivity at the same frequency,

That's how it's usually done. They often plot the fundamental frequency response and the harmonics on the same chart. There may be a note that the harmonics have been raised 20dB or whatever to get them to fit on the chart. So, you measure the distance between the fundamental and the harmonic, add the amount the harmonic was shifted and that's the difference.

Harmonic 20dB below the fundamental, harmonic shifted 20dB, total difference is 40dB or 1% distortion at that frequency.

[anli]

Originally posted by catapult
...So, you measure the distance between the fundamental and the harmonic, add the amount the harmonic was shifted and that's the difference.

Aha, I see, thanks! It is in accordance with my suggestion. The thing is I'm going to add a harmonics plot to my program ( http://gaydenko.com/qloud/ ). I think, the way harmonics are shown in datasheets is rather specious for our eyes: response decreases at speaker frequency range edges *and* harmonics decrease in sync. OTOH, near-edge behaviour seems very important to me (for example, to determine xover cut point and/or order).

Probably I'll prefer "more frankly" way - I mean separate harmonics plot where "zero level" at any frequency is a speaker response at this frequency.