It is necessary. Otherwise, how we will compare drivers objectively?
Listening comparison of different drivers is very hard and open to endless debate, especially in the bass range. Audio tastes are different between people. Objective measurements are the only way to go.
this makes no technical sense. the voltage across the voice coil (and thus its impedance) has three components:
- ohmic voltage Re*i
- magnetically induced voltage: N*dPhi/dt, ie. the semi inductive behavior of the coil - this may modulate with coil position
- Motional Back EMF x'*Bl, mass, damping and compliance determines the velocity response to motor force, the back EMF responsible for the electrical damping when the coil is driven by a low impedance source
what you describe are simply the challenges for obtaining a linear volume displacement and has nothing at all to do with the driver size. A small driver can reproduce bass with low distortion if the volume displacement is linear enough. What we present are solid methods to improve the linearity of all drivers irrespective of size and stroke
We have put the entire motor topology out in the open along with detailed measurements in our data sheets. The flux modulation (Bl modulation) is proportional to the current in the coil and the position derivtive of the inductance vs position. Consequently, haviong a flat L(x) eliminates flux modulation and also impedance modulation (its a two for one). See more includning a comparison with a standard motor in this white paper and its references including the AES paper from 2016: https://purifi-audio.com/2021/10/14/some-speaker-problems-that-needed-solving/
The field coil acts as a shorting ring no matter how saturated the ferro magentic circuit is. Saturation does reduce hysteresis distortion a bit but unfortunately not enough to solve the problem. Shorting rings help.
what do you mean?
lrisbo - nice discussion, and I would like to address all your points. But I am afraid we we are getting the audience at this forum bored. Maybe we should start a new thread elsewhere?
Tube DIY folks, what do you think?
Tube DIY folks, what do you think?
sser2,
You said:
"Complex sounds like orchestral strings, chorus, or full organ are very revealing of non-harmonic distortion, which makes the sound homogenized"
Perhaps Intermodulation Distortion is the effect you were talking about.
Now, for Newbees, a discussion of Intermodulation Distortion:
Take two frequencies, f1 and f2:
Then | f1 - f2 |, and f1 + f2 are the 2nd order Intermodulation distortion frequencies.
( '| to |' ) indicates the absolute unsigned number [non negative number]
And | 2 x f1 - f2 |, and | 2 x f2 - f1 | are the 3rd order intermodulation distortion frequencies.
Again, ( '| to |' ) indicates the absolute unsigned frequency [non negative frequency]
Examples:
2nd order intermodulation:
Start with original frequencies, f1 = 400 Hz, and f2 = 550 Hz
400 Hz - 550 Hz = -150 Hz, | -150 Hz | = 150 Hz
400 Hz + 550 Hz = 950 Hz
150 Hz and 950 Hz are the Intermodulation distortion frequencies (are not the original 400 Hz and 550 Hz we started with).
3rd order intermodulation:
Start with original frequencies, f1 = 400 Hz, and f2 = 550 Hz
2 x 550 Hz - 400 Hz = 1100 Hz - 400 Hz = 700 Hz
2 x 400 Hz - 550 Hz = 800 Hz - 550 Hz = 250 Hz
700 Hz and 250 Hz are the Intermodulation distortion frequencies (are not the original 400 Hz and 550 Hz we started with).
Another example of 3rd order intermodulation:
Start with original frequencies, f1 = 2000 Hz, and f2 = 2200 Hz
2 x 2000 Hz - 2200 Hz = 4000 Hz - 2200 Hz = 1800 Hz
2 x 2200 Hz - 2000 Hz = 4400 Hz - 2000 Hz = 2400 Hz
1800 Hz and 2400 Hz are the Intermodulation distortion frequencies (are not the original 2000 Hz and 2200 Hz we started with).
And, with 2000 Hz and 2200 Hz original tones, the 2nd order Intermodulation Distortion frequencies are 200 Hz, and 4200 Hz.
We started with only 2 frequencies, now we have 6 frequencies.
So, Harmonic Distortion is not the only distortion to consider.
Just my opinions
Originally, scientists thought that mathematically, a Bumble Bee was incapable of flying (even though it did).
Then they used the proper math, and low and behold, the Bumble Bee Could Fly!
Your music play back system might not be capable of perfect sound reproduction (none are), but . . .
Enjoy listening to it.
Yes, later you can make improvements, but listen now anyway.
You said:
"Complex sounds like orchestral strings, chorus, or full organ are very revealing of non-harmonic distortion, which makes the sound homogenized"
Perhaps Intermodulation Distortion is the effect you were talking about.
Now, for Newbees, a discussion of Intermodulation Distortion:
Take two frequencies, f1 and f2:
Then | f1 - f2 |, and f1 + f2 are the 2nd order Intermodulation distortion frequencies.
( '| to |' ) indicates the absolute unsigned number [non negative number]
And | 2 x f1 - f2 |, and | 2 x f2 - f1 | are the 3rd order intermodulation distortion frequencies.
Again, ( '| to |' ) indicates the absolute unsigned frequency [non negative frequency]
Examples:
2nd order intermodulation:
Start with original frequencies, f1 = 400 Hz, and f2 = 550 Hz
400 Hz - 550 Hz = -150 Hz, | -150 Hz | = 150 Hz
400 Hz + 550 Hz = 950 Hz
150 Hz and 950 Hz are the Intermodulation distortion frequencies (are not the original 400 Hz and 550 Hz we started with).
3rd order intermodulation:
Start with original frequencies, f1 = 400 Hz, and f2 = 550 Hz
2 x 550 Hz - 400 Hz = 1100 Hz - 400 Hz = 700 Hz
2 x 400 Hz - 550 Hz = 800 Hz - 550 Hz = 250 Hz
700 Hz and 250 Hz are the Intermodulation distortion frequencies (are not the original 400 Hz and 550 Hz we started with).
Another example of 3rd order intermodulation:
Start with original frequencies, f1 = 2000 Hz, and f2 = 2200 Hz
2 x 2000 Hz - 2200 Hz = 4000 Hz - 2200 Hz = 1800 Hz
2 x 2200 Hz - 2000 Hz = 4400 Hz - 2000 Hz = 2400 Hz
1800 Hz and 2400 Hz are the Intermodulation distortion frequencies (are not the original 2000 Hz and 2200 Hz we started with).
And, with 2000 Hz and 2200 Hz original tones, the 2nd order Intermodulation Distortion frequencies are 200 Hz, and 4200 Hz.
We started with only 2 frequencies, now we have 6 frequencies.
So, Harmonic Distortion is not the only distortion to consider.
Just my opinions
Originally, scientists thought that mathematically, a Bumble Bee was incapable of flying (even though it did).
Then they used the proper math, and low and behold, the Bumble Bee Could Fly!
Your music play back system might not be capable of perfect sound reproduction (none are), but . . .
Enjoy listening to it.
Yes, later you can make improvements, but listen now anyway.
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Btw, IMD is not the only kind of non-harmonic distortion in speaker's. There are at least 2 more, decay and border reflections.
sser2,
Thanks for reminding me about more of the many loudspeakers distortions.
A couple more 'distortions':
FM - Frequency Modulation due to the Doppler effect.
Example: A large woofer excursion at 40Hz frequency modulates a 1,000 Hz tone.
Rise Time, a slow build-up to full amplitude of a transient signal.
Example: see some tone burst tests, it is not just the ability to turn off (decay);
It is also the in-ability to come to the full amplitude on the first cycle of a multiple sine wave burst.
Yet, even with all the distortions, many of us are able to enjoy hearing music on our playback systems.
Thanks for reminding me about more of the many loudspeakers distortions.
A couple more 'distortions':
FM - Frequency Modulation due to the Doppler effect.
Example: A large woofer excursion at 40Hz frequency modulates a 1,000 Hz tone.
Rise Time, a slow build-up to full amplitude of a transient signal.
Example: see some tone burst tests, it is not just the ability to turn off (decay);
It is also the in-ability to come to the full amplitude on the first cycle of a multiple sine wave burst.
Yet, even with all the distortions, many of us are able to enjoy hearing music on our playback systems.
Very interesting, there are so many different types of loudspeaker distortion and all of them are important (more or less) and perceptible, but, according to you, equal or greater amount of amplifier distortions (of the same type, say H3) are not important?!?! Amusing...
I agree! This is an interesting discussion and potentially valuable to speaker people, so for the sake of making it easier to find for those who need this information in the future, I think it should be moved to a speaker forum.
It is sometimes hard to determine if a discussion belongs in Tubes/Valves threads or in the Loudspeaker threads (and if so, which of the Loudspeaker threads . . . Full Range or Multi-Way?).
It is sometimes hard to determine if a discussion about a Tube Guitar Amp belongs in Tubes/Valves threads or in the Instruments and Amps threads.
I do wish that Guitar Amp persons who post Guitar Amps in the Tubes/Valves threads would put in the words:
"This thread is for a Tube Guitar Amp" (right up front, in Post # 1) if they use the Tubes/Valves threads for the Guitar Amp posting.
That way those of us who are more of a Hi Fi / Stereo playback system person,
would know right away to put on our "Guitar Amp Thinking Cap" for that Tubes/Valves Posting.
Please, I hate getting all the way to post # 10 before I find out that this thread is for a Guitar Amp, not a Hi Fi / Stereo playback Amp.
Those of us who are not guitar amp knowledgeable will not know that a 'Duframis model 45x' is a Guitar Amp, and we may choose to not look up what a 'Duframis model 45x' is.
Do any Tube Guitar Amp people understand that?
Thanks to any/all of you that do tell us up front the object for discussion is a Tube Guitar Amp.
It is sometimes hard to determine if a discussion about a Tube Guitar Amp belongs in Tubes/Valves threads or in the Instruments and Amps threads.
I do wish that Guitar Amp persons who post Guitar Amps in the Tubes/Valves threads would put in the words:
"This thread is for a Tube Guitar Amp" (right up front, in Post # 1) if they use the Tubes/Valves threads for the Guitar Amp posting.
That way those of us who are more of a Hi Fi / Stereo playback system person,
would know right away to put on our "Guitar Amp Thinking Cap" for that Tubes/Valves Posting.
Please, I hate getting all the way to post # 10 before I find out that this thread is for a Guitar Amp, not a Hi Fi / Stereo playback Amp.
Those of us who are not guitar amp knowledgeable will not know that a 'Duframis model 45x' is a Guitar Amp, and we may choose to not look up what a 'Duframis model 45x' is.
Do any Tube Guitar Amp people understand that?
Thanks to any/all of you that do tell us up front the object for discussion is a Tube Guitar Amp.
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I don't see where this thread is about guitar amps at all??
(And FWIW, isn't #10 in this thread from you?)
Perhaps this thread needs a notice (maybe at post #1, mods?) alerting readers that, while pentodes are in the title, the general topic is an aspect of the amp/speaker interface - namely current driving loudspeakers using simple pentode amps. The discussion includes:
- some elements of loudspeaker distortion; and
- some amplifier configurations that may affect loudspeaker distortion
PRR,
You are correct.
My first statement did have some meaning in this current thread.
Amplifier impedance and loudspeaker characteristics, does it belong in Tubes/Valves, or in loudspeakers.
But I should not have used this thread to mention the problem of where tube guitar amplifiers belong.
That is a subject for another thread.
You are correct.
My first statement did have some meaning in this current thread.
Amplifier impedance and loudspeaker characteristics, does it belong in Tubes/Valves, or in loudspeakers.
But I should not have used this thread to mention the problem of where tube guitar amplifiers belong.
That is a subject for another thread.
We should not forget the third one:
. some elements of the intrinsic amplifier distortion
Sonce,
I love your point about intrinsic amplifier distortion.
Pluck a standup Bass, and get a particular harmonic structure.
Bow a standup Bass, and get a second harmonic structure.
Pull the string far away from the Bass, and let it fly loose. Whack! You get a third harmonic structure.
I have heard Bass players do all of these.
The same is true of intrinsic amplifier distortion.
Just how soft, or how loud, you play the amplifier changes the intrinsic distortion.
A guitar amplifier is driven at levels from soft to extremely loud; all for musical effect.
A mono or stereo amplifier is driven at levels from soft to extremely loud. Extremely loud destroys the music.
Just my observations and opinions.
I love your point about intrinsic amplifier distortion.
Pluck a standup Bass, and get a particular harmonic structure.
Bow a standup Bass, and get a second harmonic structure.
Pull the string far away from the Bass, and let it fly loose. Whack! You get a third harmonic structure.
I have heard Bass players do all of these.
The same is true of intrinsic amplifier distortion.
Just how soft, or how loud, you play the amplifier changes the intrinsic distortion.
A guitar amplifier is driven at levels from soft to extremely loud; all for musical effect.
A mono or stereo amplifier is driven at levels from soft to extremely loud. Extremely loud destroys the music.
Just my observations and opinions.
I concur that the focus of this thread is no-NFB pentode amplifier, as one possible implementation of current drive of a loudspeaker. By necessity it involves discussing the properties a loudspeaker should possess in order to be suitable for no-NFB pentode drive. As it happened, discussion at times deviated from the main focus, e.g. into a class of speakers, namely midbass, that are not suitable for the stated purpose. I am absolutely not against a good (though not really relevant) exchange of ideas, but would prefer not to stray away too far. The topic of this post is whether or not harmonic distortion is indicative of speaker quality. This is relevant to all kinds of speakers, voltage-driven or current-driven, so I am sort of bending my own rules. But I believe this small deviation is justified.
Importance of moving mass
The first graph is harmonic distortion of a Satori driver (John Krutke's web site. As one can see, the driver has very low harmonic distortion (fractions of percentage point) in the 200-500 Hz area. The second graph is cumulative decay spectrum of the same driver. Noteworthy, measurements are limited by 3 ms. The driver's "ringing" at 200-500 Hz remains relatively high amplitude at 3 ms; extrapolating, it should subside somewhere close to 10 ms.
How good or bad this is? To answer this question, we can look at the third graph, which is the cumulative decay of the Bohlender-Graebener Neo-8. Here all kind of ringing is largely gone in 0.5 ms. So, the Satori is really bad by comparison - right there at the frequencies where its harmonic distortion is lowest. Listening evaluation confirms it. Neo-8 has exquisite midrange clarity. The mid-bass drivers I've heard are muddled by comparison.
Compared to psychoacoustically benign low order HD, speaker ringing is very offensive to ear because it occurs at frequencies that have little to do with music sounds. It is perceived as veil, grit, and/or homogenization. And this very serious distortion flies completely under the radar of the HD tests.
One might ask why mid-bass driver ringing is so bad. I believe the answer is simple. Speaker's moving element can be regarded as multitude of mass-loaded springs. Once these elements are excited, their oscillation decay times are determined by damping - mechanical losses of internal friction in cone material, as well as air friction. With other things equal, ringing Q increases with increasing mass, so drivers of the same size, but larger Mms have worse ringing. BTW, ringing in midrange frequencies is not affected by electric damping.
I dearsay that high moving mass is an enemy of good mid- and high-frequency sound. There could be a metric that reflects this, "air motion index". AMI=Ma/Mms, where Ma is the mass of air in the composite Mms. The best driver will have AMI of 1. Such drivers exist, they are plasma tweeters. In a plasma tweeter the sound source is a sphere of plasma that changes its diameter to produce sound. As there is no mass involved, Ma=Mms. Electrostats and planars come second; their diaphragms are microns-thick films, almost weightless. These types of speakers have the best mid-high sound, far superior to that of any cone speaker.
From all this, the lower the Mms of a midrange driver, the better the sound quality.
Importance of moving mass
The first graph is harmonic distortion of a Satori driver (John Krutke's web site. As one can see, the driver has very low harmonic distortion (fractions of percentage point) in the 200-500 Hz area. The second graph is cumulative decay spectrum of the same driver. Noteworthy, measurements are limited by 3 ms. The driver's "ringing" at 200-500 Hz remains relatively high amplitude at 3 ms; extrapolating, it should subside somewhere close to 10 ms.
How good or bad this is? To answer this question, we can look at the third graph, which is the cumulative decay of the Bohlender-Graebener Neo-8. Here all kind of ringing is largely gone in 0.5 ms. So, the Satori is really bad by comparison - right there at the frequencies where its harmonic distortion is lowest. Listening evaluation confirms it. Neo-8 has exquisite midrange clarity. The mid-bass drivers I've heard are muddled by comparison.
Compared to psychoacoustically benign low order HD, speaker ringing is very offensive to ear because it occurs at frequencies that have little to do with music sounds. It is perceived as veil, grit, and/or homogenization. And this very serious distortion flies completely under the radar of the HD tests.
One might ask why mid-bass driver ringing is so bad. I believe the answer is simple. Speaker's moving element can be regarded as multitude of mass-loaded springs. Once these elements are excited, their oscillation decay times are determined by damping - mechanical losses of internal friction in cone material, as well as air friction. With other things equal, ringing Q increases with increasing mass, so drivers of the same size, but larger Mms have worse ringing. BTW, ringing in midrange frequencies is not affected by electric damping.
I dearsay that high moving mass is an enemy of good mid- and high-frequency sound. There could be a metric that reflects this, "air motion index". AMI=Ma/Mms, where Ma is the mass of air in the composite Mms. The best driver will have AMI of 1. Such drivers exist, they are plasma tweeters. In a plasma tweeter the sound source is a sphere of plasma that changes its diameter to produce sound. As there is no mass involved, Ma=Mms. Electrostats and planars come second; their diaphragms are microns-thick films, almost weightless. These types of speakers have the best mid-high sound, far superior to that of any cone speaker.
From all this, the lower the Mms of a midrange driver, the better the sound quality.
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Of course low harmonic distortion is ONE OF THE INDICATIVES of loudspeaker quality. But if OTHER non-linearities are much bigger, low distortion alone is no longer relevant. How difficult is this to comprehend?
Obviously, for someone it is very, very difficult to comprehend this simple logic: if two different non-linearities exist in one loudspeaker, both must be low, for good sound quality!
If one of the non-linearities is very bad, then it is absolutely of no relevance if the other non-linearity is exceptionally low. How difficult is this to comprehend?
Besides, you are comparing apples and oranges. Again.
In this case, you are comparing midbass driver (Satori) to (mid)tweeter (NEO-8)!? Basically, you are comparing a woofer to a tweeter! Are you serious?
NEO-8 can not, and must not, work below 500 Hz! On the other side, Satori (and any other midbass) will happily work below 500 Hz. Did you made a listening evaluation of NEO-8 in the 100 Hz - 500 Hz range? I can bet the NEO-8 will sound muddled and very distorted by comparison to Satori in the 100 Hz - 500 Hz range, in spite of the much lower diaphragm moving mass Mms.
May I remind you of your preferred three-way loudspeaker with crossover frequencies 120 Hz and 800 Hz?
But it IS in the radar of the cumulative spectral decay ("waterfall") measurements! Of course distortion test can not measure waterfall diagrams! Are you serious?
You have to look at many different loudspeaker measurements, to declare which driver is good or bad.
Wrong! There are plenty of waterfall measurements to prove you wrong on this. Mms has to be optimal for the cone driver - not too large, but also not too small. For any conventional cone midbass driver from 3" to 15", very small Mms (in his group) means very thin and light cone, prone to resonances which results in a very bad waterfall diagram!
Also, your mantra "lower Mms -better sound quality" contradicts your previous believing:
How on earth 12" midbass driver is better than 6.5" driver, when 12" midbass driver has much bigger Mms compared to any midbass 6.5" driver?
On Mr. Krutke's web site, ALL mid-bass drivers tested have bad waterfall in the mid and upper mid ranges. Essentially, they have bad waterfall over their entire working range. Local 2 ms would be quite an achievement for this kind of driver. With typical tweeter crossover point of 3-4 K, one should be content with poor quality of midrange due to ringing in these drivers.