I'm a casual and some what lazy student on the topic. There are many authoritative books on the subject. A google search for "electro acoustics of microphones and speakers" will yield a list of books. You may find a .pdf of a book for free. It may require some searching to find one that goes through the acoustic and mechanical equations of motion directly for a microphone and a speaker. Here's an example I found. https://www-fourier.ujf-grenoble.fr/~faure/enseignement/musique/documents/chapter_1_sound/microphones_and_loudspeakers/Glen Ballou - Electroacoustic Devices_ Microphones and Loudspeakers-Focal Press (2009).pdf
To really bend my brain last year I decided to study vinyl records to produce a mathematical simulation of the signal chain from cutting head to phono cartridge playback. Figuring out what the groove displacement profile represented ( velocity? acceleration? something in between?) required a lot of study to sort through industry terms I found confusing.
To really bend my brain last year I decided to study vinyl records to produce a mathematical simulation of the signal chain from cutting head to phono cartridge playback. Figuring out what the groove displacement profile represented ( velocity? acceleration? something in between?) required a lot of study to sort through industry terms I found confusing.
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Thanks for telling me what I'm looking for, I need a punch, not a thunderous roar and I need the fastest possible acceleration of the speaker
Thanks for the info, I know it's not reasonable to drive a speaker designed by crazy people, however I really want to know how they drive it (Those parameters seem unreasonable, it's a Devialet Mania speaker, it has a minimal box, and I'm using a class D tl494 (pointless adding transistors) to drive it, and it works perfectly. But you know, class Dtl494 operates at 110khz)
The Devialet Manta is a portable powered speaker that includes amplification and equalization that is likely very optimized for the driver. So you are bypassing that? I expect it has a low impedance driver to enable a very low battery power supply voltage.
This is counter-intuitive. If it moves faster, the sensitivity will be higher. If there were anything to try and keep up with it would have to try that much harder to do it.
Yes, the speaker has both mechanical resonance (Qms) and electrical resonance (Qes) which combine as Qts. The mechanical resonance has independent influence on the cone over the driving signal, thus modifying the Q.
Referring to 'accuracy' makes it sound like there's a problem. If the resonance Q changes, surely that's a feature and not a distortion?
The change in Qts may not be significant, or detrimental. It all comes down to "it depends".
If the cone displacement follows the applied force linearly, there is no distortion. Of course this is a utopian view that is not reality. So the question becomes, how non-linear? Then, how to fix it? To be perfectly honest, I'll take a speaker that is as reasonably close and be happy with it.
Every technology has its drawbacks. I just want to live with the thing, and everything is a lot better than it was in the 1960s and 1970s, that's for sure.
If the cone displacement follows the applied force linearly, there is no distortion. Of course this is a utopian view that is not reality. So the question becomes, how non-linear? Then, how to fix it? To be perfectly honest, I'll take a speaker that is as reasonably close and be happy with it.
Every technology has its drawbacks. I just want to live with the thing, and everything is a lot better than it was in the 1960s and 1970s, that's for sure.
Thought experiment time.
The cone is always going to follow the applied signal. The more mass, the more far behind, the more sluggish it's going to follow ( likely a phase delay mostly uniform across the surface of the cone (*) and static in the frequency domain.
This distance shift is energy... a hysteresis effect. And it combines both the movement of the mass of the cone ( F = ma ) and the back EMF from the coil. That energy is going to be superimposed on the signal imposed by the driving amplifier.
Again, mass is important, very important. The less mass the lower Force required to accelerate the driver- F(t) = ma(t), where mass is constant ( Phew! ).
The one thing I've wondered, where is that energy coming from? With a constant magnet in the speaker assembly we can not get the energy from the magnet... but what if we have an electromagnet in the speaker engine?
Say, an electrostatic speaker or a Field Coil design? In both cases, there is an external source of energy into the driver, so that can sink the EMF, freeing the amplifier from providing a sink for that....
https://www.audionote.co.uk/e-ltd-speakers
So, with such designs... does the damping of the audio amplifier even matter? Can an tube OTL drive such speakers better even though it has high output impedance - and a pretty crappy damping factor...
(*) This is a first order approximation and assume the cone is completely rigid and its behavior doesn't change with frequency.
The cone is always going to follow the applied signal. The more mass, the more far behind, the more sluggish it's going to follow ( likely a phase delay mostly uniform across the surface of the cone (*) and static in the frequency domain.
This distance shift is energy... a hysteresis effect. And it combines both the movement of the mass of the cone ( F = ma ) and the back EMF from the coil. That energy is going to be superimposed on the signal imposed by the driving amplifier.
Again, mass is important, very important. The less mass the lower Force required to accelerate the driver- F(t) = ma(t), where mass is constant ( Phew! ).
The one thing I've wondered, where is that energy coming from? With a constant magnet in the speaker assembly we can not get the energy from the magnet... but what if we have an electromagnet in the speaker engine?
Say, an electrostatic speaker or a Field Coil design? In both cases, there is an external source of energy into the driver, so that can sink the EMF, freeing the amplifier from providing a sink for that....
https://www.audionote.co.uk/e-ltd-speakers
So, with such designs... does the damping of the audio amplifier even matter? Can an tube OTL drive such speakers better even though it has high output impedance - and a pretty crappy damping factor...
(*) This is a first order approximation and assume the cone is completely rigid and its behavior doesn't change with frequency.
Hi Tony,
OTL amplifiers are a misuse of a device. Tubes are limited in current capacity when you consider currents required in dynamic loudspeakers. That is why a matching transformer is used. Those old engineers, they really knew what they were doing after all. Yet some folks still second guess them.
I'm working on a pair of Acoustat Servo-Charge amplifiers. They drive panels directly - a correct use for a tube. With 5,000 VDC B+, not a great environment for transistors. Each device type has an optimal use case.
As for speakers, you have cone mass and also air mass. That is non-linear with force. As for a dynamic magnetic field, sure you can dump more energy into the system. With a DSP and input signal, this may well be a great error correction system. Doesn't have to be perfect, it would probably be much better than what we have now. Mount that coil externally, maybe behind or inside the magnet structure. We will generate more heat in the process. I guess we would have something called a "correction amplifier" in addition to the amplifier driving the voice coil.
OTL amplifiers are a misuse of a device. Tubes are limited in current capacity when you consider currents required in dynamic loudspeakers. That is why a matching transformer is used. Those old engineers, they really knew what they were doing after all. Yet some folks still second guess them.
I'm working on a pair of Acoustat Servo-Charge amplifiers. They drive panels directly - a correct use for a tube. With 5,000 VDC B+, not a great environment for transistors. Each device type has an optimal use case.
As for speakers, you have cone mass and also air mass. That is non-linear with force. As for a dynamic magnetic field, sure you can dump more energy into the system. With a DSP and input signal, this may well be a great error correction system. Doesn't have to be perfect, it would probably be much better than what we have now. Mount that coil externally, maybe behind or inside the magnet structure. We will generate more heat in the process. I guess we would have something called a "correction amplifier" in addition to the amplifier driving the voice coil.
Tony, we may need to get a few things straight before moving forward.
See my post# 65 Mass is not a problem.
Mass does not cause a delay.
Mass is a linear property, hysteresis is a nonlinear effect.
F=ma.
I don't know how you're looking at this... but I'm looking at the basic physics of it. A force is applied to the speaker and it must move accordingly. It does not move instantaneously, there is a time delay. Efficiency has little to do with this... at best for a given force applied, a higher efficiency of the system will minimize the time lag between the force application and the motion of the piston itself.
Mass is static but it affects the energy required to move it, and the acceleration ( I think velocity is an issue too, but it's more of a function of time.. v(t) for a given input force ).
The delay between the speaker moving to the applied force is in the time domain, not the frequency domain... the speaker lags the electromotive force. You can not refute that as it is basic physics!
The equations on this are rarther straightforward... it's Newton's classic mechanics and a little bit of Maxwell's E&M for the electro motive force.
I don't know how you're looking at this... but I'm looking at the basic physics of it. A force is applied to the speaker and it must move accordingly. It does not move instantaneously, there is a time delay. Efficiency has little to do with this... at best for a given force applied, a higher efficiency of the system will minimize the time lag between the force application and the motion of the piston itself.
Mass is static but it affects the energy required to move it, and the acceleration ( I think velocity is an issue too, but it's more of a function of time.. v(t) for a given input force ).
The delay between the speaker moving to the applied force is in the time domain, not the frequency domain... the speaker lags the electromotive force. You can not refute that as it is basic physics!
The equations on this are rarther straightforward... it's Newton's classic mechanics and a little bit of Maxwell's E&M for the electro motive force.
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Mass doesn't cause delay. It may cause a phase shift, which is a different thing in this case.
The current drive folks will not agree with the need for a huge damping factor. Given that the DC resistance of most drivers is about 75% of the impedance, it seems pointless to ask for a damping factor more than 10/75% =~ 13. It could be argued that the best damping factor is one, since it deals with both parallel and series resonances.
I think it is a mistake to think of cone movement or velocity in the time domain, except as it relates to physical limits. Hearing and sound are frequency domain systems, as are damping and resonance.
I think it is a mistake to think of cone movement or velocity in the time domain, except as it relates to physical limits. Hearing and sound are frequency domain systems, as are damping and resonance.
[ using lots of output tubes ]
https://www.google.com/search?q=otl...FMi03LjGgB91BsgcFMi03LjG4B6IO&sclient=gws-wiz
https://www.google.com/search?q=otl...FMi03LjGgB91BsgcFMi03LjG4B6IO&sclient=gws-wiz
The phase shift.... that is, the cone moving BEHIND the driving signal is exactly what I'm describing... a distortion in the time domain!
I think you and I are discussing different things.
And I believe it causes IM, which we do hear.
OK, basic physics:
a = F/m = 2F/2m = 3F/3m = ...
So, if you have more massive woofer cone, you must push it with more F, to get equal acceleration which lighter cone has. How you can do it? With stronger magnet, or more precise - with bigger Bl. Simple!
Why equal (given) force to the more massive woofer cone? Why not more force?
Moral of the story: no time delay difference between high-mass cone with bigger magnet and low-mass cone.
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MASS of the cone + restriction of suspension + the ENERGY of the 'motor' = Rise time / Transient response / Speed & Delay.
ANY amount of 'time delay' introduces phase response effects.
Once again > the use of square waves with microphone & oscilloscope WILL reveal interesting things.
For some reason this method of additional testing is rarely used 😎
ANY amount of 'time delay' introduces phase response effects.
Once again > the use of square waves with microphone & oscilloscope WILL reveal interesting things.
For some reason this method of additional testing is rarely used 😎
Simple reasons
(1) More force from amp... more distortion, more noise
(2) More force from speaker, where does it come from? The magnet. The magnet doesn't generate energy, it's the interaction of the current through the coil going through the magnetic flux... how does the magnet react to it?
Need to look into the fundamentals behind the equations... that's Physics.
That's the reason I bought up electro magnets in the speaker assembly instead of a permanent magnet. In such a magnet you can apply ( and dissipate ) energy, thus it can keep its magnetic field constant as the coil moves about the magnetic field.
If the flux of the permanent magnet is being affected, then that's going to be a distortion.
That's why I enclosed the write up from the Audio Note people... interesting. he's not giving away his IP (Intellectual Property) but hinting at it.
Why do speakers heat up? Do the permanent magnets warm up too as they absorb energy from the effects of the coil's current.. that's back EMF.
And, how do you know there is NO time delay? Is current instantaneous? Does the voice coil move instantaneously when a current is applied to it in a magnetic field?
Notice the purely mechanical analysis of mechanically closely coupled systems doesn't work for a speaker that is loosely coupled via electro mechanical forces. The mass will resist the movement...
That why a while back I brought in the Plasmatronic... pretty much a massless device. It's dynamics are superb!
In a speaker with significant mass and static/sliding coefficients of friction, there will always be a time delay between the position of the driver and the signal that was fed to it. 99.99% of all speakers have such mass and friction.
Please don't quote me variations of F=ma.... in reality the equation is F(t) =m dot a(t). There's a lot of meaning in there. Think about what the models are telling you and how the system is working... actually, it's a model, but that's Physics for you.
So back to my original observations...
Postulate: The lower the mass of a speaker, the lower the friction of the motor and the more invariant the field of the driving motor's magnet the lower phase shift between the driver and the driving signal. Such a phase shift is a time domain distortion and a cause of heat.
Also, derivative of the postulate: The lower the mass of a speaker, lower friction (..) and invariant quality of the driving magnet, the less back EMF is created and the less need for the driving amplifier to provide and energy sink ( damping factor ).
And one more... most amplifiers use the GND as the return... so they may not care so much about the back EMF as it goes to ground. But how about amplifier designs... like a bridged device, or push pull, where the return doesn't go to ground but sees instead another driving device pulling current?
Those topologies would be more affected by the "constriction" in the return path and more affected by back EMF.
Check this out.. https://www.diyaudio.com/community/threads/voice-coil-inductance-le-and-transient-responce.15968/
(1) More force from amp... more distortion, more noise
(2) More force from speaker, where does it come from? The magnet. The magnet doesn't generate energy, it's the interaction of the current through the coil going through the magnetic flux... how does the magnet react to it?
Need to look into the fundamentals behind the equations... that's Physics.
That's the reason I bought up electro magnets in the speaker assembly instead of a permanent magnet. In such a magnet you can apply ( and dissipate ) energy, thus it can keep its magnetic field constant as the coil moves about the magnetic field.
If the flux of the permanent magnet is being affected, then that's going to be a distortion.
That's why I enclosed the write up from the Audio Note people... interesting. he's not giving away his IP (Intellectual Property) but hinting at it.
Why do speakers heat up? Do the permanent magnets warm up too as they absorb energy from the effects of the coil's current.. that's back EMF.
And, how do you know there is NO time delay? Is current instantaneous? Does the voice coil move instantaneously when a current is applied to it in a magnetic field?
Notice the purely mechanical analysis of mechanically closely coupled systems doesn't work for a speaker that is loosely coupled via electro mechanical forces. The mass will resist the movement...
- A body remains at rest, or in motion at a constant speed in a straight line, unless it is acted upon by a force.
That why a while back I brought in the Plasmatronic... pretty much a massless device. It's dynamics are superb!
In a speaker with significant mass and static/sliding coefficients of friction, there will always be a time delay between the position of the driver and the signal that was fed to it. 99.99% of all speakers have such mass and friction.
Please don't quote me variations of F=ma.... in reality the equation is F(t) =m dot a(t). There's a lot of meaning in there. Think about what the models are telling you and how the system is working... actually, it's a model, but that's Physics for you.
So back to my original observations...
Postulate: The lower the mass of a speaker, the lower the friction of the motor and the more invariant the field of the driving motor's magnet the lower phase shift between the driver and the driving signal. Such a phase shift is a time domain distortion and a cause of heat.
Also, derivative of the postulate: The lower the mass of a speaker, lower friction (..) and invariant quality of the driving magnet, the less back EMF is created and the less need for the driving amplifier to provide and energy sink ( damping factor ).
And one more... most amplifiers use the GND as the return... so they may not care so much about the back EMF as it goes to ground. But how about amplifier designs... like a bridged device, or push pull, where the return doesn't go to ground but sees instead another driving device pulling current?
Those topologies would be more affected by the "constriction" in the return path and more affected by back EMF.
Check this out.. https://www.diyaudio.com/community/threads/voice-coil-inductance-le-and-transient-responce.15968/
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As good and as convenient as it may be, it shows no more than a phase and/or response plot.