If the whole cone is not moving in unison there is distortion. Is that what you meant?
@oldhvymec --

So 101 on speaker building for me is know what your talking about..
My terminology may not be the as eloquent as the word salad connoisseurs, BUT my personal observation and understanding of "bass distortion" seems to conflict with most of "New way" of thinking..

FIRST; PHASE PLUGS are the ONLY way to decrease bass distortion properly on all round cone drivers "second wave". OR Don’t use cone drivers, OR Don’t use large surface area drivers.. The is NO OTHER WAY...

I’m far less complicated here using large coned, high efficiency drivers presently from ~615Hz and down - "second wave" be damned; (per channel) two of them ported (~85 to 615Hz) and the last one is loaded in a tapped horn to cover the rest of the range down to some 20-25Hz. At SPL’s that shakes the air and surroundings quite violently the TH woofer moves or rather vibrates about a mm at most (it can move up 18-20 mm peak to peak), while the main speaker dual woofers don’t visibly move at all (less cone movement means less inertia build-up, and more cone area means better air coupling). For all intends and purposes the 15" woofers here all stroll along at levels that are viscerally felt. The compression driver and large horn (more than 5 sq. ft. mouth area) that covers the remainder of the frequency span from ~615Hz on up sports a 111dB sensitivity, and rarely see more than a single watt from the amp feeding them actively. They’re cruising while I’m potentially bruising, if you get the picture. In both cases distortion is vanishingly low, despite claimed 2nd waves and stated high compression ratios - even approaching decibels that are ear shattering in a home environment.

If I were to be discouraged by notions not to use large diffraction horns (much) deeper than 12" in a home environment nor large coned HE woofers due to second wave distortion, I’d be an important experience so much poorer. As an example quite a few people rave about the waveguides used in JBL’s more recent monitors, and yet compared to an older and much(!) larger EV diffraction horn with its landmine big CD they sound small and almost malnourished - the 4367 waveguide indeed mode-y and strident - and less relaxed and full. Commercially large size doesn’t sell, but I’d go so far to say that with horns in particular it’s the one ingredient that makes a substantial difference. There’s no working around that, even if it means refining flare geometries from a smaller size - period. Indeed, the larger the horn the less it sounds like a horn, or like two friends, both audio buffs, who heard my EV system the other day, said: "It sounds like ESL’s on steroids."

Lot’s of reasons not to go big with speakers, pro segment not least, but I’d say most of them are preconceived rather than coming from actual experience. Just my $0.02..
I’m far less complicated here using large coned, high efficiency drivers presently from ~615Hz and down - "second wave" be damned;

<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>..

It is the main reason for distortion other than VC overheat (change in resistance). Like I said if you can keep ANY secondary wave from coming back on ANY driver you’ve done something few have.

I found the speed of most driver and Voice Coils a LOT of extra weight. I like domes but there are some HEAVY ring and dome drivers out there. Still great dispersion with domes with a minimum of combing.. (I gotta finish that one)

I use 3 different designs now. The RMx Elixirs modified is the best so far. Hybrid line array dipole. Separate poles, no common driver front to rear. It’s NOT OB. 93% E. They are getting spring isolation too with 1.5" of Butcher Block base. They are made of HDF. With the new base, added rear enclosure and a 17 lb AC tweeter little over 480lbs each.. They are mass loaded.. LOL Narrow baffle neo 8 planar design..

The bass sections in all my monitors NOW are separate or not used.

I have two project yet to finish. that really address the WHOLE "second wave" issue.

1. Narrow baffle Line array of domes/rings and a single AC G1 tweeter

2. Narrow baffle Line array of neo 10 planars and a single AC G1 tweeter

Both about 72" long, for an 8 foot ceiling, 84" for 9 foot ceilings.

Yikes.. that was a long one.. Jeeeeez OP say something. :-)

Hands are feeling good.. Use them while I can.. AY?

Master M how goes the acoustic journey? Adjustable spring BASS traps  (pipe organ tech) coming up..:-)

I'll post.. pics pretty quick.. I'm being lazy...

Regards
Master M how goes the acoustic journey? Adjustable spring BASS traps (pipe organ tech) coming up..:-)
It takes me a lot of listening and some enhancement device trick to succeed, but much time... 2 weeks of listening and fine tuning, but i had 29 pipes and tubes ...This is finished now.... 😊

My last idea comes directly from the last acoustical research ,but i am proud to be the sole creator of my design... Like you are for your speakers...

We listen not to frequency like assume those who use an electronic equalizer and a mic with a tested response frequency for a PRECISE ARTIFICIAL location...

We listen to some multi dimensional complex different wavefronts, a bunch of frequencies,( like the voice timbre of a singer) coming from the tweeter, the bass drivers, and from early and late reflections in a PRECISE NATURAL time frame...

I used this fact creating my H.M.E. (Helmoltz mechanical equalizer): imagine a snake with head and tail...

The HEAD begins a few centimeters from the tweeter of one of my speakers with 2 pipes near the tweeter and 2 bottles near the port hole; then going to my left on the first reflection point with 6 pipes; then to my rear with the MAIN BODY of the snake, 8 pipes ,one 8 feet high; and then goes to the second reflection point to my right, with 6 pipes and finally ends at the TAIL, with 3 pipes near the bass driver of this speaker, with one bottle near the port hole....Asymmetric distribution of pipes and bottles and differences between them are very important at the head and tail....

Result: "listener envelopment" factor LEV and "source width" factor ASW and imaging complete optimization...

This means my 50 dollars speakers sound like almost the best speakers there is to my ears, with ONLY their design normal limitations and no more limitations from the room now... In the opposite, my room enhanced the speakers design to MY EARS (not to a mic from a mic)...

It seems you were the only one to catch something about my idea with your comparison with silent organ pipe acoustical tuning in church.... This was half of my idea.... The other half is related to the way the ears/brain recreate the FIRST frontwave sound coming from the 2 speakers early and late reflections for each ear.... The gist of my idea is to control these different reflections with a qualitative control different for each ear...This is the powerful head and tail of my acoustical snake or H.M.E. we can also reduce his name to a true "Helmholtz grid".... Speakers were not there tough at the time of Helmholtz....


Acoustic is so powerful that it is the main factor in audiophile perceived experience... The failure to understand this push the market obsession with upgrading electronics parts....There is less difference between each electronics parts at ANY cost than between electronic part in a bad or in a good room... PERIOD....

The tragedy is : it is not all people who can experience it in a dedicated room....The rest is audiophile blind history obsession with all that matter the less, cables,analog/digital,tubes/S.S. etc, at the cost of which really matter the most: acoustic....

NO ONE listen to his speakers only...We listen to our room.... The direct waves coming from the speakers are perceived, even in near listening field, MIXED with the reflections.... In my own room in one second the waves cross the room 80 times horizontally and more vertically ( my room is 13 feet square 8 1/2 feet high)....My ear/brain use a 80 milliseconds window, in which already many crossings(direct,early and late reflections) will be analyzed internally from EACH one ear... When people think that near listening field nullify the powerful impediment of their non controlled room this is completely false....Any change in my own acoustical settings were detected by me in nearfield listening or regular one position alike...


My best to you....