IT cant....I dont think.....I dont profess to be an expert but an excess of acceleratory force is no bad thing surely?
I dont disagree with all that has been said by the way. I just dont understand how anyone can say a driver with a better BL/MMs or accn can be worse than one with a slower accn, all else equal.
I just believe a high BL is desirable, just as a stuffed TL with its flattened impednace characteristic, is also desirable, for a good transient response.
mms/BL is indeed not a good measure trying to "rate" dynamics/resolution, it discards too many vital parameters.
Personally I don't think that these specific T/S params tell the complete story, I rather look for sheer cone area when I'm after dynamics/resolution (my mid is 15" and the compression driver is 3"). And since most any good working large cone drivers are pro stuff with sometimes crazy motors (larger high eff midrange drivers, notably, google up 18sound 10M600 for example) it is natural to overrate their other properties besides Sd by mistake, also because those pro driver also are more linear IF the motor is linear because the high feedback/damping decreases other distortions more than with a lesser motor -- cone is less "clamped" by the back-EMF and this back-EMF is less linear, with weaker motors.
Personally I don't think that these specific T/S params tell the complete story, I rather look for sheer cone area when I'm after dynamics/resolution (my mid is 15" and the compression driver is 3"). And since most any good working large cone drivers are pro stuff with sometimes crazy motors (larger high eff midrange drivers, notably, google up 18sound 10M600 for example) it is natural to overrate their other properties besides Sd by mistake, also because those pro driver also are more linear IF the motor is linear because the high feedback/damping decreases other distortions more than with a lesser motor -- cone is less "clamped" by the back-EMF and this back-EMF is less linear, with weaker motors.
I've wondered a bit about the different claims as to what gives a speaker better subjective dynamics. Since "dynamics" seems to be an elusive concept to define (it isn't, really), there seems to be a number of different camps championing high BxL, low Mms, high BxL/Mms, low R (e.g., through oversized wire cross-sections), high Sd, and so forth. Eventually, I realized that all these things influence the efficiency of the driver:
(Copied from Thiel_small_analysis)
There is even a term rho for the density of air, which becomes pretty large in the throat of a horn, well known to give "good dynamics"!
Is it really so simple as "higher efficiency = better subjective dynamics"?
(Copied from Thiel_small_analysis)
There is even a term rho for the density of air, which becomes pretty large in the throat of a horn, well known to give "good dynamics"!
Is it really so simple as "higher efficiency = better subjective dynamics"?
Yes!!!!!
I agree that Bl/Mms is not a very good indicator of dynamics. But stronger motor+light cone gives better dynamics than weaker motor+heavy cone. At least that much is established by the above equation.
Of course, the counterargument is that you can provide more power and get the same absolute SPL, but it isn't the same as having a high efficiency driver. You start getting into issues with excursion, linearity and the ability of the amp to deliver more current.
I believe 'badman' on this forum said something on another thread that was relevant:
"if you can see the cone move regularly, you haven't got enough speaker"
yes lol......Mms/Sd is important for me when choosing a driver, and despite all of this thread and my (perhaps fumbling) input, I have never used the ratio MMs/BL to select a driver.
Klaus' posts seem highly relevant and logical though. At least there are others that feel low Qts or higher BL drivers arent the spawn of Satan.....efficiency and BL just HAVE to correlate with transient dynamic capability, though its clearly NOT as simple as just that.
Very interesting papers....
Klaus' posts seem highly relevant and logical though. At least there are others that feel low Qts or higher BL drivers arent the spawn of Satan.....efficiency and BL just HAVE to correlate with transient dynamic capability, though its clearly NOT as simple as just that.
Very interesting papers....
Quote
Of course, the counterargument is that you can provide more power and get the same absolute SPL, but it isn't the same as having a high efficiency driver. You start getting into issues with excursion, linearity and the ability of the amp to deliver more current.
Excursion linearity depends on the linearity of B (admitting length L is constant in the gap) and of the suspension, not of a high value of BL.
Of course, the counterargument is that you can provide more power and get the same absolute SPL, but it isn't the same as having a high efficiency driver. You start getting into issues with excursion, linearity and the ability of the amp to deliver more current.
Excursion linearity depends on the linearity of B (admitting length L is constant in the gap) and of the suspension, not of a high value of BL.
Exactly so. The fine-print is the specific physical equivalent of the word 'and' above. High BL typically results in a more dominant and more linear damping term BL²/Re, while the influence of compliance k_s and the other factors in the force equation (in that high-BL AES paper) is effectively lower than with less damping. A high-BL driver can lower any ill-effects by allowing more feedback except for voice-coil related issues which are outside the loop.
It all comes down to a lucky combination of all the side effects whether a driver will be killer or not. High efficiency drivers IME have a tendency to do generally better, but that is just an opinion.
All the above is assuming regular voltage drive to establish the feedback within the driver as described. With different drive impedances the mechanisms change in their parameters... another variable (or degree of freedom).
---:---
High Q of the mechanical system (Qms) should also be noted as possibly playing a role wrt dynamics/detail. Some woofers with excessive forced-air cooling, siliconed spiders etc are pretty much nonlinear in their mechanical compliance and damping (think turbulences, hysteresis, creep, eddy currents, etc) and tend to sound blurred in spite of their monster motors. I fully support this from my limited experience, I ususally look for a two-digit Qms but less is not a show-stopper for preselection.
- Klaus
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What a great topic ! 
I was wondering a lot of time how to choose a driver to get the better "dynamic"... I read all the topic and I don't really get an answer, except the fact that dynamic isn't a realistic statement.
Btw, I should understand that two well optimised systems "Amplifier + Box + Driver" could do strictly the same result in transients and impulse response even with very different BL/Mms.
Is that correct ?
I was wondering a lot of time how to choose a driver to get the better "dynamic"... I read all the topic and I don't really get an answer, except the fact that dynamic isn't a realistic statement.
Btw, I should understand that two well optimised systems "Amplifier + Box + Driver" could do strictly the same result in transients and impulse response even with very different BL/Mms.
Is that correct ?
As has already been explained here, a cone has to be in sync with a signal to have a flat FR. A high bl and low mms have no advantages in this context.
If one wants max detail, then obviously avoid distortion. But also its possible that less flex and more rigidity in the entire moving mass, especially the cones, might have a positive effect. So low mechanical damping and pistonic behavior could in theory help.
If one wants max detail, then obviously avoid distortion. But also its possible that less flex and more rigidity in the entire moving mass, especially the cones, might have a positive effect. So low mechanical damping and pistonic behavior could in theory help.
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