When does speaker distortion become audible?

When you got garbage speakers!!

I'd be wary if you don't have good a/b capability. You may be listening to truncated information. The highs are critical to spatial presentation and what you were hearing before may have been a truthful exposure of the source limitations. I have a number of tubes, cables, and capacitors trialed in my system that eventually exited because they were doing information subtraction.

Most of the speakers have overhunged motors (narrow gap, long coil) producing a lot of distortions especially at longer excursions (bass). Underhung motors (big magnet, wide gap, short coil) produce less distortions (are more linear) but are more expensive and not very common. Acoustic Zen Adagios have "underhung" woofers. Underhung is sometimes even used in tweeters to reduce distortions at high power (long excursions) - Morel Supreme 110.

http://www.gattiweb.com/images/delta_design/Supreme110.pdf

Hi Kijanki, please put a face on the point you made about speaker distortion. IOW, ... is speaker distortion measured in percentages?? What are considered respectable distortion stats as a function of frequency? To what extent is it fair to assume that beyond a certain SPL, speaker distortion rises quickly, kinda' like when an amp clips.

Is it also fair to assume that the higher the magnetic flux density as measure in Gauss, the more control the magnets will have over the cone, thereby lowering distortion. For example, the magnetic flux density of my tweeter and midrange drivers is 20,000 and 15,000 Gauss, respectively. I have no clue if these are good, bad, neutral or irrelevant stats.

Happy Holidays,

Bruce

According to Robert Lee of Acoustic Zen speakers operating at power higher than 10W can get 10-12% of distortion. Most of it comes from the woofer and is less audible.
Here is fragment of interview with Robert Lee:

"That is a good point and I would like to say this. There are thousands of speaker manufacturers worldwide but so far I have identified less than ten who employ underhung drivers. I think that underhung drivers are the best solution to reduce harmonic distortion in the bass. No one ever talks about the huge amounts of THD in the low frequencies, especially when you are playing things loud. Most drivers create from 10-12% THD when you listen at over 10 watts. If you are listening to 10 watts through your speaker system, you get 5% harmonic distortion. So what are you listening to? When people design amplifiers, they rate them at 0.05% harmonic distortion. Meanwhile even at modest volume levels, your low-frequency drivers put out 5% or greater harmonic distortion so nobody can listen at even low levels and achieve true purity with low distortion, never mind concert levels.
That's why I selected to use both the underhung driver and a ribbon tweeter of my own design."

As for the flux density your assumption seems logical to me but perhaps speaker builders can chime in?