When does speaker distortion become audible?

At 20 Hz it was over 5% but according to this article:
http://www.bksv.com/doc/BO0385.pdf
it is harder to hear distortions below 400Hz. Single tone shows only THD but there are other distortions that might be more audible. Intermodulation, caused by nonlinear motion and membrane bending, produces new frequencies when speaker is driven by two frequencies.

According to this article: http://publications.lib.chalmers.se/records/fulltext/126969.pdf
THD testing does not reveal all nonlinearities of the speaker. Harmonic distortion will alter instruments' overtones adding coloration while intermodulation distortion will be much more audible.

Kijanki,... I started reading the article. It's fascinating. It looks like it really speaks to a fallacy in cold reading bench test reports in general and those relating to speakers in particular. Namely, the bench tests may be testing stats that are not terribly important, and not testing stats that may be important. Ergo, why live auditioning is so important.

When does speaker distortion become audible?

My answer is simple. It's always audible.

Since it seems safe to assume that no speaker is audibly perfect, all speakers can be presumed to distort the signal that is provided to them to an audible degree. And most likely in multiple ways.

And, hypothetically speaking, even if there were a speaker that is audibly perfect in some rooms, it would undoubtedly not be perfect in many or most others.

Regards,
-- Al

Makes sense Al. Moreover, listening to a sonically perfect speaker might be figuratively like drinking triple distilled pure water. Pure H2O -- yes. Taste good, not really.

Hi BIF, what does it take in your mind to come up with nonsensical lines like this,
"Sustained listening at 100 db will rupture the organs in small animals and damage one's hearing."

And not put a smiley face after it:)

"If the first 100db suck, why continue?"
PHP143