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

This thread really separates the knowledgeable from the clueless.

Who's on first?

heating of the components in the crossover will add to compression

Heat also alters the XO points and not uniformly between drivers.

Your welcome!  

@larryi

Not only does heat affect the voice coil, to the extent the heat gets into the magnetic structure, flux is affected which further adds to thermal compression.

Yes That is one of the many reason for using ALNICO in permanent magnet speakers, it's impervious to heat so it's flux is not affected by the change in temperature.

Finally, I might add that although the paper does not mention this, heating of the components in the crossover will add to compression.  

You are correct I think you can fix that with an active crossover. 😁

 

You’ve got more to worry about in passive crossovers than heat

 

VERY good information to add to my (limited) knowledge base.

Might also explain why it's extremely difficult for me to endure the 3rd (and featured) act of live performances?  As the evening progresses, the "tech" running the sound board bumps the sound levels up a few db during intervals.  By the time it gets to the 3rd set, it's downright painful.  The additive effects of distorted, dynamically compressed sound accompanied by much louder average sound levels is not what an aging audiophile appreciates at a live music venue.

@ditusa --

"Yes That is one of the many reason for using ALNICO in permanent magnet speakers, it’s impervious to heat so it’s flux is not affected by the change in temperature."

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

... there was one major disadvantage in Alnico loudspeakers that would have to be addressed � the susceptibility to permanent demagnetization due to overpowering.

This phenomenon is a result of variability in strength of the permanent magnetic field caused by interference from the voice coil�s electromagnetic field. This is referred to as flux modulation and is a leading cause of distortion in any dynamic loudspeaker. The electromagnetic field generated in the coil pushes against the global magnetic field set up by the permanent magnet and return circuit, causing it to �bend�. Under normal operating conditions, Alnico magnets actually resist this bending better than most other magnet materials. However, should this shift become large enough, it will exceed the coercivity of Alnico and cause it to partially demagnetize.

http://www.audioheritage.org/html/projectmay/technology/1500al.htm

Though in most cases, not least with high efficiency drivers used domestically I gather there are no real drawbacks with Alnico magnets to speak of.

@fiesta75 --

"You’ve got more to worry about in passive crossovers than heat"

Not least that they’re there in the first place, and their more complex iterations usually make matters worse. Heat at some point only adds to those issues, and used in low efficiency speakers this will only be more prevalent.

High eff. horn speakers ideally, or at least often call for steep filter slopes to avoid out-of-band irregularities, and as such active filters offer themselves much better here compared to passive XO’s.

 

Good info on Alnico magnets. They can be re-energized fairly easily too. I still enjoy them even with the increase Neodymium offers

The overpowering demag was mostly or only affecting a few JBL models when the switch was made from low tube power to higher power SS in PA use it is not an issue for other alnico magnet drivers. But it is still passed around as affecting all Alnico and that is just wrong I have dozens of old Alnico drivers meeting spec after lifetimes of use.

@johnk --

Thanks for clarifying. Had no intention to put down Alnico magnets in any way, in fact I'd only cherish their inclusion in a speaker setup.  

I have woofers and midrange compression drivers that utilize alnico magnets.  I don't plan on abusing these drivers to the point where de-magnetification occurs.   A local dealer who had an alnico magnet driver with weak output had the magnet recharged, it did not cost that much to have this done.  I have no idea about the particular effect of the type of magnet employed in a driver, as far as the sound is concerned, except that many of the drivers I like happen to have alnico magnets (and pleated paper surrounds, and other old school design features).

Thermal distortion from my speakers. My ears would blow first! :)

@pcrhkr —

“Thermal distortion from my speakers. My ears would blow first! :)”

One of those instances where it may feel inappropriate stating that this is actually a desirable outset :) Question is if you would know whether thermal distortion/modulation had krept in in the first place, because that’s the real bug for the ones in particular who don’t have high efficiency speakers (and speakers that are passively configured to boot), and at what juncture - much earlier than one would imagine - it may pose an issue. In your case it may be a lesser issue than what many other audiophiles (unknowingly) are facing, at least.

the real bug for the ones in particular who don’t have high efficiency speakers

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.

 

This gentleman understood the importance of speaker efficiency. See link below

Enjoy! That's what it's all about! 😎

 

Mike

http://www.lansingheritage.org/html/jbl/reference/technical/efficiency.htm

Or not. I never liked recording in Auxberger rooms.

@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

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

I concur.

 

Mike

The interesting thing about Alnico magnets and compression is that some theorize that the particular sound of Alnico magnet speakers is that they are actually subject to more compression than other magnet types because flux density is lower under dynamic conditions when the voice coil is excited. 

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.

@ieales 

The industry moved away from higher efficiency because its expensive, when solid state power became available. Sometime during the 1960s it became obvious that transistors were substantially less expensive than tube power. So with the less expensive power came speakers that were less efficient because (no surprise here) the speaker manufacturers could make more money. As tube popularity waned, output transformers and the tubes themselves became progressively more expensive; meanwhile solid state power got cheaper.

But prior to all that, the industry moved away from field coil to permanent magnets, not because permanent magnets were better, but because they were cheaper as well! In a similar way, CDs were cheaper than LPs on both the record side and playback side.

Whenever you see movements like this, in audio traditionally its always been about increasing profit. There are things that fly in the face of this a bit, for example some manufacturers have learned how to reduce thermal compression in less efficient drivers by proper venting of the pole piece, allowing for greater cooling (although things like that can be applied to higher efficiency too...); IOW they are trying to improve the product rather than make more money on it. But that sort of thing is rare.

 

The question was rhetorical 🙄

 I posted because I feel many over-fixate on known or obscure issues without realizing nothing is or can be perfect all is flawed. 

As Atmasphere described, cost was a big driver to higher power and lower efficiency.  But, it was also partly a result of the success of stereo.  When it was just one box, it wasn't quite so bad that the box was big in size.  But, when stereo came along, there was a big push toward making smaller speakers.  Smaller size meant lower efficiency, but, that tradeoff was now possible because the transistor made it possible to get more power relatively cheaply.  

 I posted because I feel many over-fixate on known or obscure issues without realizing nothing is or can be perfect all is flawed

I guess Easter week is as good a time as any to get philosophical, but even my almost 40 year old speakers have sounded close to perfect for 3+ decades.

Or at least they offer a close enough taste, to convey the perfection of the thoughts.

but even my almost 40 year old speakers have sounded close to perfect for 3+ decades

I'll wager that just replacing the caps would astound you. Nothing fancy, just polypropylene for electrolytics and Mylars [<<--- N A S T Y]. Erse and Dayton are plenty good.

Solder any and all push on connections.

I know because I BTDT for decades... 😎

If your speakers come from the likes of Spica, buy a couple of extra of each cap and match* as closely as possible to stock films. 40 year electrolytics are going to have an ESR that's likely off the charts.

* Requires a capacitance meter or a pal with one.

But prior to all that, the industry moved away from field coil to permanent magnets, not because permanent magnets were better, but because they were cheaper as well!

That is correct.

@larryi,

The interesting thing about Alnico magnets and compression is that some theorize that the particular sound of Alnico magnet speakers is that they are actually subject to more compression than other magnet types because flux density is lower under dynamic conditions when the voice coil is excited.

I think they are confusing dynamic instabilities within the voice coil with compression, I could be wrong. Also, JBL uses Alnico 5dg magnets. The 4dg and 3dg magnets are lower in strength as some design require less strength. Just when you thought you had perfect sound. LOL 😎See link below: Suspension Bounce as a Distortion.

Mike

 

This "thermal compression" issue really impacts those that listen for long periods at higher levels.     In the studio where I go often, this is a MAJOR problem affecting lots of speakers. Active ones and especially passive ones. Cheap drivers or entry level speakers with little cooling can be heated up (long hours of loud music) and become "power compressed".  The effect is distortion but also more than that: its reduced dynamics.  For many tracking engineers, the reduced dynamics of the speaker is THE major issue affecting their work as tracking live sources requires intense dynamic range.  

I don't think there are many consumer customers listening at high levels for hours on end.

Brad