Thermal Distortion your loudspeaker most likely suffers from it. But do you care?
Thermal Distortion is much more serious than just a maximum power handling limitation or side effect.TD is overlooked by most manufacturers as there is no easy (low cost) solution and TD is audible and measurable most of the time at most power levels. TD is caused by the conductive metal (aluminum, copper, or silver) voice coil getting hotter when you pass electrical energy through it. The more power you pass through it the hotter the metal gets. The hotter the metal gets the more the electrical resistance increase. The efficiency goes down and you need to ram in more and more power for smaller and smaller increases in SPL. It can be the reason you get fatigued while listening. If you are running massive power you are creating more TD in your transducers. But do you care? And is it a reason some prefer horn-loaded designs or SET-powered systems since they have the least problems with TD?
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.
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.
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!
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.
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.
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.
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.
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 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.
''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
@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?
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.
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!
"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."
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.
“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.
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).
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.
"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.
"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.
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.
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. 😁
Thank you for the interesting paper you attached to one of your postings. I just got around to reading it and it is very interesting. 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. I also did not consider that changes in Thiele-Small parameters also add to compression. Finally, I might add that although the paper does not mention this, heating of the components in the crossover will add to compression.
Please pardon my ignorance, but I am confused by the references to liquid metal wires or liquid metal passive preamps. What metal that is liquid at room temperature is used to make this equipment? How is it contained so that it can't leak out?
Can anyone confirm my lay understanding that Zobel Networks do, in fact, have a significant, if not great, effect on the SQ when applied correctly to a speaker?
AKA, “Deulund-Mundorf Ultra Speaker Purifiers” sold on AG.
Crossover components most certainly can get hot enough for thermal compression to be an issue. A friend of mine who repairs gear showed me a couple of inductors he took out of a pair of speakers that where played at a really high volume level. Remarkably, the drivers were not blown, but the plastic formers for the inductors completely melted--what was left was a spool of wire sitting in a pool of plastic.
"Back when tubes were king, high efficiency speakers were very common because tube power was (and continues to be) expensive.
When solid state amps were commonplace, speaker efficiency started to go down.
The problem here is that it never helps to have an amplifier drive a speaker that is a difficult load and in particular low efficiency. The result will be higher distortion from the amplifier if nothing else, and that distortion usually manifests as higher ordered harmonics, to which the ear assigns the tonality of 'harsh and bright' and is keenly sensitive to their presence since it uses them to sense sound pressure.
So we've been hearing 'harsh and bright' for 50 years now. Some is the fault of amplifier design of course, but difficult to drive speakers don't help.
So inefficient and low impedance speakers should be avoided if you want to get the most out of your amplifier dollar investment."
But what makes a speaker a difficult load also and not least involves the effects of passive cross-overs (unless this is implicit to what you're saying here, but it's unclear to me) in terms of their complexity and the (steep) phase angles presented, not to mention smearing of the signal here.
This is interesting due to observations I've made going from passive to active speaker designs (with the same speakers), where I've found going active with solid state amps makes for a sound more akin to the sonic imprinting of SET's; passive sounds more sluggish, heavier even and less resolved (but to some more pleasing this way), whereas active makes for a more transiently clean (less smeared), less grainy and more liquid and open presentation. Easier on the ears, and more fleshed out.
I'd have cherished the opportunity of using 16 ohm versions of the drivers used in my speakers (not least the compression driver, which is available in a 16 ohm version), having then both high efficiency, high impedance and passive filter-less speakers. I would assume though passive filters and their negation to be a similarly or even more important means of making the amp seeing into an easier load, certainly bypassing more complex passive filters. A "purer" low impedance load seems preferable to a higher ditto marred by steep phase angles, but I guess it also depends on the specific amp.
Modern high powered amps (400+ watts) that can run into a 1 ohm load can certainly burn pretty much any low impedance device up. How much heat is developed depends entirely on current flow which depends in part on the impedance of the load, lower impedance devices being more likely to heat up. How fast depends on the amount of heat sink is available for the device and how well it is ventilated.
The most significant problem is not thermal distortion but failure of the device. Modern voice coils with Kapton formers are surprisingly tolerant. Although resistance does increase with temperature the effect is minimal. It might skew the frequency response of the speaker a little and decrease output or available power but it will not cause IM or Harmonic distortion. You can read about the effect here https://www.cirris.com/learning-center/general-testing/special-topics/177-temperature-coefficient-of-copper and here, https://en.wikipedia.org/wiki/Power_compression#:~:text=In%20a%20loudspeaker%2C%20power%20compression,power%20of%20the%20audio%20amplifier.
Thermal compression can be a problem in large commercial concert systems. It is not a significant problem in home HiFi systems. It would best be characterized as inaudible. The sky is not falling and you need not go looking for 16 ohm loudspeakers. Take a deep breath and say,"OOOOOOOOHMMMMMMMM....
Back when tubes were king, high efficiency speakers were very common because tube power was (and continues to be) expensive.
When solid state amps were commonplace, speaker efficiency started to go down.
The problem here is that it never helps to have an amplifier drive a speaker that is a difficult load and in particular low efficiency. The result will be higher distortion from the amplifier if nothing else, and that distortion usually manifests as higher ordered harmonics, to which the ear assigns the tonality of 'harsh and bright' and is keenly sensitive to their presence since it uses them to sense sound pressure.
So we've been hearing 'harsh and bright' for 50 years now. Some is the fault of amplifier design of course, but difficult to drive speakers don't help.
So inefficient and low impedance speakers should be avoided if you want to get the most out of your amplifier dollar investment.
Pannels don't suffer from it but they have their own design limitations related to limited excursions, dipole effect cancellations, beaming, and pannel size reducing higher frequency. Nothings perfect.
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