Thermal Distortion your loudspeaker most likely suffers from it. But do you care?

@ieales --

"If high efficiency speakers are so darned good, why did the industry move away from them? So electronics makers could sell more expensive Power? Methinks not."

Actually more power got less expensive with the advent of the transistor, at which point Edgar Villchur also made his entry with his "acoustic-suspension" AR-1’s as a much smaller and much less efficient speaker package - a package that needed the extra power, of course.

It was and largely still is about (size-)convenience and the introduction of a mass domestic market, albeit at the time (and reiterated today by the likes of John Atkinson) it was sold off with the marketing bling as offering the same extension from a fraction of a size with less distortion. What’s not to like?

Well, Mr. Atkinson was (and likely still is) an avid supporter of MQA, so let that seep for a while like a good Earl Grey.

In the context of this thread it’s about thermal compression/distortion/modulation, and there’s no escaping physics here with regard to overall size requirement of a speaker system that naturally accommodates high efficiency, and thus is much more impervious to thermal issues.

The question though also seems to be: does it matter, or how much does it matter in a domestic environment with typically moderately sized listening rooms? Here’s a quote from yet another fine article supplied by poster @ditusa on the subject of efficiency:

"In all fairness, this limitation in dynamic range [with a small, inefficient speaker system] is of little interest to many listeners. At "average" loudness, neither type of system is apt to be momentarily overloaded. But the difference can be easily demonstrated under the right conditions. The man who wants to hear the smash of cymbals, the "bite" of a Steinway grand, a full concert intensity, will not be able to duplicate these sounds readily with a bookshelf-type loudspeaker system.
"This is all very interesting, no doubt," says the prospective costumer, "but you still haven’t told me which type of system is better."
The answer is that if all other considerations can be ignored, a good big system is almost always better than a good small system."

http://www.lansingheritage.org/images/jbl/reference/technical/efficiency/page03.jpg

a good big system is almost always better than a good small system

provided one has the space to accommodate the system. Many a good big system has been utterly compromised in a space too small or with another failing where a smaller less efficient system would shine.

For ½ century, I've been telling people the room is part of the system and it's possible to buy the best of and end up with unlistenable!

 

I would not claim to be an expert on thermal dissipation through a conductor which travels through a magnetic field.  However through the  decades of experience in electronics and and a hobbyist at speaker building I do know that the speakers that I used have a  vented pole  piece which aids in keeping the speaker cool while in operation. Also it has a large magnet which helps, large compliance, spider to aid control. Most quality high excursion woofers use this design for that very reason. There is much science applied when figuring the "thermal factor "  My woofers came with technical blue prints showing Q, free air resonance, magnet weight, cone mass , pole gap magnet strength. and so on. So what?  As back EMF is created by a speaker conductor going through large excursions  the thermal distortion is minimal compared to other factors.  One of which and foremost the power amplifiers ability to deal with back EMF which is the reverse movement of the cone throughout music reproduction. I tested several high quality, high current,  solid state amplifiers that could not deal with it and distorted before the speakers did. In my case the best bang for the buck was a quality tube unit. The cones move more, no distortion. That was one of many examples. Matching the type of speakers with the best amplifier makes a huge difference. Also, if you exceed the rated RMS continuous rating to get great dynamics, then you are mismatched. This factor remains true with tweeters and mid range drivers as well.  Most important is the end result, sound. My comments are strictly for completely passive speakers. Thermal problems causing audible distortion is the least factor to be concerned with.

@johnk are we talking about compression? Or something else?

 

I would not claim to be an expert on thermal dissipation through a conductor which travels through a magnetic field.

Me too.

 

However through the decades of experience in electronics and and a hobbyist at speaker building I do know that the speakers that I used have a vented pole piece which aids in keeping the speaker cool while in operation. Also it has a large magnet which helps, large compliance, spider to aid control. Most quality high excursion woofers use this design for that very reason. There is much science applied when figuring the "thermal factor "

If we are talking about compression, then I believe that that sets in on the order or milliseconds, and not minutes, so it is not a long term event.

 

My woofers came with technical blue prints showing Q, free air resonance, magnet weight, cone mass , pole gap magnet strength. and so on. So what? …

Did they have compression plots?

 

 

As back EMF is created by a speaker conductor going through large excursions the thermal distortion is minimal compared to other factors. One of which and foremost the power amplifiers ability to deal with back EMF which is the reverse movement of the cone throughout music reproduction. I tested several high quality, high current, solid state amplifiers that could not deal with it and distorted before the speakers did. In my case the best bang for the buck was a quality tube unit. The cones move more, no distortion. That was one of many examples.

I am pretty sure that tube amps are renowned for having a low damping factor compared to SS amps.
(Or do I have that backwards?)

And I am also pretty sure that back EMF is primarily addressed with amps that have a high damping factor?

 

Matching the type of speakers with the best amplifier makes a huge difference.

Agreed.

 

Also, if you exceed the rated RMS continuous rating to get great dynamics, then you are mismatched. This factor remains true with tweeters and mid range drivers as well. Most important is the end result, sound. My comments are strictly for completely passive speakers.

If the speakers have instantaneous wattage specs, then it could make it easier?
What would be the sound of compresssion limiting?

 

Thermal problems causing audible distortion is the least factor to be concerned with.

It is something that is likely of more interest to people that like higher dynamic range recorded music.

I’l boil down yo answer to “No”.
… Where this was the question:

Thermal Distortion your loudspeaker most likely suffers from it. But do you care?

''Alnico magnet’s were/are sometimes prone to demagnetize:''  Yes!

My understanding is: The JBL LE15A 15'' Alnico woofer has a top plate of more then 1/2 an inch thick, short coil, long magnetic gap, the flux density in the voice coil gap is 11000 gauss, hence it will not demagnetize itself when hit hard with high level input power. That's one of the reason why its considered to be the best vintage 15'' Alnico woofer JBL ever made. Also Alnico is the best for making permanent magnet speaker drivers, Alnico stability and resistance to back EMF is really good. JBL engineers discovered that more then 75 years ago. That is the reason why JBL chose Alnico 5dg magnet for the JBL1501Al-2 woofer, not Ferrite nor Neodymium. Enjoy! That's what it's all about! 😁 

IMO Ferrite is basically a lousy magnet material for speakers but it is cheap and readily available. 

Mike

''The new 1500Al used in the S9800 can take continued pulses of 5000 watts and loose no more than 1%. The test can only be done a few times before the coil is destroyed, but the magnetic assembly is totally stable.''-Greg Timbers JBL engineer

http://www.lansingheritage.org/html/jbl/specs/pro-comp/2215.htm

http://www.atma-sphere.com/en/resources-common-power-amplifier-myths.html