Hi Brian!
> From the time you start to mention motor strength,
> you're talking about Qes, not Qms.
Motor strength is relevant to Qms and Qes.
> Which is exactly what will be happening if Qes is
> low. There is a direct correlation between Qes and
> the ability of the motor to stop and start cone
> motion - the lower the Qes, the greater this
> ability. Therefore, in this case the output
> characteristics of the driver are primarily
> dependent on Qes.
Yes, thats motor braking. But I've already described the significance of Qms. From about 10 to 12, is about when the cones getting pretty loose, and distortion and harmonics in these types of devices is typically much higher than others. From about 20, it just gets real bad. I've not overlooked Qes at all - in fact, I've used that on a number of occasions, and stated drivers that absoluetely require an amp thats a good current sink/source, and also, others when its "less needed". Qms describes mechanical damping and motor strength and cone weight are relevant to this, and Qes is the ratio of series motor circuit resistance to the square of BL, or basically electrical damping.
The main purpose of this was originally distortion - and I described how high mechanical Q speakers typically have much higher harmonics and ringing because of the way they are built. But on this side-discussion thats branched out, both Qms and Qes tell the story of the motors filter characteristics.
> I haven't come across any drivers with Qms that
> high. The highest I've seen is Qms=12. In any case,
> you're likely to find that, even with those
> drivers, performance is more affected by Qes, which
> is usually an order of magnitude smaller than Qms.
I agree, theres little drivers with Qms of 20, but Parts Express do have some when I was flicking through their catalogue. These "mudmotors" I talk about absolutely require motor braking, and I described high Qms speakers having very low DC resistance and a requirement of an amplifier with good damping factor - but these still have triple digit distortion figures, and thats a real bad thing. So these ones will be worse, even once taking advantage of motor braking. But not all manufactures do this, and some will make both Qms and Qes very high, and therefore Qts too, and these motors just plain suck, lots of overring.
One look at Qms - and the motor with Qms of 12, probably has a lot greater control over the cone at resonance than one with a Qms of 20. But these devices still "arn't as good". You've overlooked the important of Qms in my last post, and how the driver is constructed.
> Nope. The motor braking won't be infinite - it's
> dependent on the driver's Qes :-).
Yes, but the wire is just about infinite damping - DC resistance and BL still has the ability to change Qes.
Just because the cone seems stiff when we tap it with the terminals shorted - you see the effect of motor damping, but you dont know how much system performance is affected. Sure, electrical damping does play a major part in how the driver is damped - my argument is that high Qms speakers have a poor design to realize maximum bass extension, and the driver is not balanced for anything else, and have high distortion at resonance and high harmonics too. You know the ones I'm talking about - you've seen them, and you've probably avoided them too, and we've all joked about it. Its the one you hear blaring from that kids racing car down the street, with the really crap sound system installed. They just go to Wal-Mart and buy a 50 dollar woofer and stick it in one of those wedge-shaped pre-made boxes. Then the trunk lid rattles and they think it's cool.
So getting back to the main argument; the magnetic structure is the prime contributor to distortion. These high Qms mudmotors typically are built very poor to realize maximum bass extension which necessitates poor motor contol, an on devices like this, it's the case that they've cut costs in attempt to tune the woofer very low, and thats the reason they have to tune their woofers this way. And on poor motors like these often they'll use really crap non-symmetrical cheap magnets and these drivers are the ones with triple digit distortion. It all comes back down to how the manufacture decides to "spend his money". That doesn't mean all high Qms speakers are mudmotors, but all these "mudmotors" I've seen - typically sound real bad, and typically, most designed this way are. Theres much more 80Hz and 120Hz and such harmonics being generated from speakers like this, and thats distortion which we can avoid - using better parts.
Adrian
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