-addendum:
..under operational load.
The AIC drivers from 18 Sound are also better in this respect, under operational load.
Doppler Distortion in loudspeakers
"Both are just different descriptions of the identical physical phenomenon to which Doppler's name has become attached. Siegfried also said that "I have not seen the associated PM pointed out in text books, but it follows from FM or PM modulation theory" - this is really the crux of what this article is about - that no textbooks describe the phase change (and resulting phase/ frequency modulation) as the cone moves closer to or further away from the listener, and this leads to a general misunderstanding as to the real cause of the effect, and obscures other effects that could have been extrapolated had this been more widely known. More to come on this aspect shortly, but rest assured that it will not make a large difference to the way we design (or listen to) loudspeakers, but simply explains other phenomena that were not seen or predicted previously."
Lots of people have shown preference for field coil and Alnico magnets. Alnico interests me in particular because the material is described as electrically conductive, which makes me wonder whether it also has characteristics of a shorting ring. Has anyone measured the impedance of drivers using these?
-addendum:
..under operational load.
The AIC drivers from 18 Sound are also better in this respect, under operational load.
Thanks
Thank you Jack!
This is exactly what I have been driving at and finally gave up.
You don’t have to drive LF speakers to within a MM of it’s life to hear this.
Barry.
Chris, in your rush to make some point important to you, you seem to have forgotten all about T/S parameters. Saying a cone (and coil and former) aren't heavy compared to air is just crazy.
A woofer I have has a max displacement of 15.5 mm and a surface area of .08 m2.... and a cone weight well over half a pound (261 grams*). If air weighs what you say it does, then under a full head of steam, that half pound cone is trying to set in motion .0015 kg of air.
I can't claim to be sure of this model and I hope others will correct me and add smarts to the discussion.
But sure seems futile to try to accurately accelerate and decelerate a half pound object in really, really, thin air. At least it is futile without some feedback loop.
B.
*these weights are just nuts. It is due to the marketing department (and to certain mischievous viewpoints on this forum) that insist on making woofers that can absorb more power than my kitchen toaster. But if you are experimenting with motional feedback, ahem, ahem, you really do want to do your breadboard testing with a blast-proof driver.
Last edited:
Ben,
Did you click the link I posted?
The driver there would be much more to your distate than anything with a measly 261g Mms. Yet, the driver in question produces spectacularly good results when used below a couple of hundred Hz.
I also see no problem with using a heavy thing to move a light thing. The heavy thing is still under extreme control from the motor.
Chris
Interesting because that's the mic I now see on Google searches. But a couple of years back it was something else, not Beyer, and very expensive. Similar look, but slimmer. Will continue to search for it. Anyway, I think it was just an array of small electret capsules.
EDIT. Might have been the Microtech Gefell KEM 975 I saw.
I'd have to agree with Chris, I simply don't see any relevance to the diaphragm mass as far as performance goes. We are talking about LF drivers here and their impulse response need not be that "fast" to be accurate. Even if "fast" were required, that's just a matter of increasing the force.
Sure, given air as the medium, the efficiency exchange (radiation efficiency)is greatest when the diaphragm mass density equals the air mass density, but it does this over an ever narrower bandwidth. What one usually wants is reasonable efficiency over a much wider bandwidth, meaning a much heavier cone. Add more force and you get what we all use now a heavy cone, big magnet woofer. Its HF performance is more dependent on how well the cone suppresses the rim resonance (surround), which is usually the first major cone breakup mode with any significant effect.
-transients (dynamics). (..inertia and momentum with the heavier cone/pole-vc and the necessarily *chunkier surround & spider.)
..and a whole host of problems with the driver in regard to (much) higher mass drivers (and engineering it to perform moderately well).
Still, over-build drivers with a good motion-sensing/correction (servo) system can effectively overcome this limitation at low and very low freq.s..
-um, yeah: chunkier - a new technical term.
..and a whole host of problems with the driver in regard to (much) higher mass drivers (and engineering it to perform moderately well).
Still, over-build drivers with a good motion-sensing/correction (servo) system can effectively overcome this limitation at low and very low freq.s..
-um, yeah: chunkier - a new technical term.
Generally low mass high BL drivers have good dynamics. Look at a typical full range like the 8" audio nirvanas or some of the pro drivers like B and C. They can keep up with horns even.
However thats not the whole story because a more rigid cone will also deform less and so produce less smear of the signal. So this also effects dynamics.
Looking at a typical full range with a light cone you also find weak bass output. There is a physical reason why lighter cones can't produce deep bass. Someone who knows more about this can explain this better but they can't resonate down low. But I think with a non-zero impedance they can produce more bass. They are often used in horns which produce bass differently.
However thats not the whole story because a more rigid cone will also deform less and so produce less smear of the signal. So this also effects dynamics.
Looking at a typical full range with a light cone you also find weak bass output. There is a physical reason why lighter cones can't produce deep bass. Someone who knows more about this can explain this better but they can't resonate down low. But I think with a non-zero impedance they can produce more bass. They are often used in horns which produce bass differently.
If you take a woofer and you look at the impulse response of the filter that will drive it, the slew rate just isn't very large so the "dynamics" argument doesn't have a good basis in fact. AT any rate all the terms and effects that are being used are subjective and don't have any real analytical basis (not that anyone cares about the science behind audio!!)
Servo control doesn't change anything. Servo would be a good solution to nonlinearity (if such a thing were actually a problem.) In fact servo control of loudspeakers has been tried and tried again and still no product sticks in the marketplace. There's a reason for that.
PS - I use a heavy cone 15" speaker in my system and the dynamics are outstanding. I'd look elsewhere for an explanation of "dynamics". It has interested me for a long time and I have investigated many ideas, none of them has panned out to explain this completely subjective aspect of audio. I believe its there, but its not any of the obvious things - like cone mass, nonlinearity, thermal modulation, its none of those.
Servo control doesn't change anything. Servo would be a good solution to nonlinearity (if such a thing were actually a problem.) In fact servo control of loudspeakers has been tried and tried again and still no product sticks in the marketplace. There's a reason for that.
PS - I use a heavy cone 15" speaker in my system and the dynamics are outstanding. I'd look elsewhere for an explanation of "dynamics". It has interested me for a long time and I have investigated many ideas, none of them has panned out to explain this completely subjective aspect of audio. I believe its there, but its not any of the obvious things - like cone mass, nonlinearity, thermal modulation, its none of those.
Last edited:
Dynamics as normally described is a perception. There are lots of complicated reasons for perception. I had used a pair of JX125 which has a pretty good low frequency resonance, and it produced very low frequency of organs in a small room. Have no memory of the dynamics.
With a low mass, the cone is easier to stop at the extremes where the BL generally gets lower, this is when using a suffer spider generally seems to help as well. I think the shape of the spider Km is going to have an effect.
With a low mass, the cone is easier to stop at the extremes where the BL generally gets lower, this is when using a suffer spider generally seems to help as well. I think the shape of the spider Km is going to have an effect.
Last edited:
I agree with both of the previous posts. Dynamics are not something that are easily quantified and remain a subjective term. But anyone who's listened to a good compression driver or line array knows that dynamics are real, and for some of us an important quality.
Cranking your little clock radio is not dynamics. It has to do with the effortlessness and efficiency with which sound is radiated into the air. There's an authority to the sound. I believe horns create an impedance match between the driver and the air that conducts sound more efficiently, and so have an advantage here. Line arrays as well just rip into the air even at lower volumes. An increase in the size of the wave front is part of what does this. There are likely some obscure and complicated physics involved here.
Lack of dynamics could be considered distortion, though again this is an area not well understood.
Cranking your little clock radio is not dynamics. It has to do with the effortlessness and efficiency with which sound is radiated into the air. There's an authority to the sound. I believe horns create an impedance match between the driver and the air that conducts sound more efficiently, and so have an advantage here. Line arrays as well just rip into the air even at lower volumes. An increase in the size of the wave front is part of what does this. There are likely some obscure and complicated physics involved here.
Lack of dynamics could be considered distortion, though again this is an area not well understood.
Once again, Dr. Pangloss* tells us we are living in the best of all possible worlds, citing again his modest-scale speakers.
It has been the historic movement of audio to enlarge the feedback loop and that includes speakers. Sealed boxes do provide a measure of feedback in the form of degenerative control. BR and false-horns do not. There is no sure path to error correction except by means of feedback.
While to my knowledge all those who have tried motional feedback have been enthusiastic about the benefits, making it work commercially is very difficult. I think the basic problem is that the Rice-Kellogg driver is as silly a concept as using an internal combustion engine to power a vehicle***. What engineer in their right mind would create a woofer system where the oscillation point is within the working passband?** Which means you have to manage the feedback loop while the phase relationships are doing summersaults.
B.
* Voltaire's Candide
** engineering issues are somewhat more benign north of the woofer band
*** zero torque at stall
Last edited:
Phase linearity plays an important roll in preserving spacial information. Polarity is also important, but for some reason, after I linearize phase response of a system, polarity difference is not so obvious.
Dynamics is the next thing I am trying to improve. Although making the speaker residual sound decay faster does improve perceived dynamics, the dynamics of the attack transients still is not improved nearly as much as I would like.
Dynamics is the next thing I am trying to improve. Although making the speaker residual sound decay faster does improve perceived dynamics, the dynamics of the attack transients still is not improved nearly as much as I would like.
Yes they are deforming a lot and the peripheral region of the cone don't move enough... the bass is coming from a very restricted surface around the coil.