LRDDMC Loudspeaker Resistor Drive Distortion Measurement Challenge

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#101
Current distortion measurement is just reflecting the fact that the 20R resistor isn't causing current distortion - as you'd expect of any resistor.

As you increase the series resistor value, current is progressively defined by the resistor, not the driver under test.

The "test" is therefore meaningless.
 
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#102
I don't get where this comes from. It was not meaningless to me, it shows I can pick up almost any woofer and improve distortion by using a high drive impedance. 20 ohms is not supposed to be some magic value, just a practical value compatible with most setups which is sufficient to expose the effect.
 
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#107
What is interesting is that the benefits appear to occur above the bass frequencies, but at frequencies where parameter variation with excursion would be relatively minimal - and voicecoil inductive reactance (and its effects) relatively insignificant.

Maybe we're looking at the effects of parameter variation with drive current? And is this a driver with high Le, for instance? But then, if so, why do benefits diminish at higher frequencies? How does cone material affect results? It's difficult to extrapolate based on a lone example.
 
#109
There are a bunch of Klippel posters and PDFs available which explain the various distortion mechanisms and how to differentiate them. There is Bl(x) and Le(x) which change with excursion, and there is Bl(i) and Le(i) which change with current. I would be looking at the current dependent distortion mechanisms since excursion decreases with frequency.
 
#112
Regarding parameter variation with drive current, for small excursions in the midrange, you wouldn't really expect much difference between voltage and current drive. Also, you'd reduce that by using a driver with decent flux density (large magnet).
 
#113
#114
It strikes me that some clues to the source of distortions could be found by analysing drive current with voltage drive (and/or drive voltage with current drive).

Also, analysis of IMD, as opposed to the (somewhat more straightforward) HD could well prove very illuminating.
 
#116
tmuikku said:
Here some IMD measurements by Esa Meriläinen he posted on Finnish forum
Click to expand...

Wow! Some comprehensive, well documented tests for once! The improvements with current drive seem so large that one wonders just why this sort of thing hasn't come to light before. My only caveat would be the methodology's weakness in matching levels - also noted in their post #6.

It would seem to be a nice idea for some rigorous subjective (listening) testing to be done to verify audibility...
 
#117
Yeah, Esa wrote the book some years back and has got some opposition and downplaying I think, difficulties getting papers out and so on. Perhaps partly about the "tone" of his text, perhaps partly because audible differences aren't that much with proper systems, who knows. Also, it is likely hard to sell such systems as the speaker is married to the amplifier they would need to be sold together. Today active systems are pretty common so it's likely going to have some traction at some point, it's slow turning industry I think, with lots of safeguarding, old geezers maintaining their position.

Luckily, we don't need to mind any of that in DIY land. Learning that it's all about impedance in series with the driver it doesn't matter if you have a voltage or current amplifier, it's about the circuit impedance, and one could tailor it to liking. Active speaker with regular voltage amplification and DSP, few passive components mixed in, could reap benefits cheaply and basically employing "normal" practices, no any special stuff needed to work out mechanical damping and such. Few currency units to few passive components and bam, distortion got lowered some. Even current drive amp and suitable speaker is doable, if DIYer wants to.
 
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#118
Today active systems are pretty common so it's likely going to have some traction at some point, it's slow turning industry I think, with lots of safeguarding, old geezers maintaining their position.
Click to expand...
The B&M active speakers with motional feedback used current drive from the beginning (i.e. some decades ago). But the main motivation was the cancelling of the Lvc's effect on frequency response, making a control loop around the driver more feasible if the effect of that pole given by Re and Lvc is cancelled out by the use of current drive. The lacking damping around fs is handled by the control loop in this case.

Regards

Charles
 
#120
For sure. In general I bet part of 1st order passive xo system appeal is here in, and not all in "phase" as often associated. Although, both distortion and phase are quite tough to hear. Some people seem to prefer passive xo speakers to active for some reason, and I cannot figure out any other reason than elevated impedance in series with the drivers. Because, whats the difference of DSP and passive xo? If transfer functions were matched only the circuit impedance is assuming DSP is fine quality. Using both passive parts and DSP would be superior to either alone as now circuit impedance and frequency response can be tailored independently. Trade-off is in cost and complexity, but cost and complexity are not audible issues and thus trade-off worth taking if good audio quality has higher priority than cost and complexity.

Some myth busting: How about short and thick audiophile cables? what if I told ya sound was better with thin and long cable, the cheap one, that has some extra resistance to it? Or, what if worse amplifier damping factor sounds better? Well, not sure if I hear any difference with my setup, if there is some it's not too obvious for some reason. Well, these examples cannot be generalized to all cases, but knowing details how this stuff works would help to choose wisely and avoid marketing trap, at least encourage experimentation.

Anyway, on active speaker any woofer could take series inductor, perhaps parallel notch (in series) for breakup. Tweeters could utilize series resistor and parallel inductor as high pass and attenuation, instead of typical series cap and L-pad. Add DSP and you've got ingredients optimize FR, phase and some distortion.
 
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