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View Full Version : Servo drive midrange?



thadman
11-19-2006, 06:56 PM
I've seen several implementations of servo-drive technology (theres an article outlining it in this months Audio XPress) in subwoofers, but not midranges where we are most sensitive to distortion.

After reading up on diyaudio.com, I've come to the conclusion that most distortion from a driver is due to non-linearities in excursion (BL isnt flat).

From my understanding, the servo-drive units (measuring acceleration) apply different amounts of power throughout the stroke making its excursion more linear. Why hasnt this been done for midranges?

Is the active technology inept at responding fast enough in the midrange?

Would it be possible to create a *passive circuit* after measuring a driver (doesnt dayton offer a speaker measurement setup?) and its specific BL curve and applying power at the inverse of the curve (more power at the extremes) to make the BL more flat?

TC Sounds has introduced a *passive* answer to this solution by designing the voice coil around the BL curve (varied amount of windings)...why hasnt this been done on midranges?

Beat_Dominator
11-19-2006, 06:58 PM
I think the processing is not fast enough.

thadman
11-19-2006, 07:16 PM
How many times does it measure acceleration throughout the stroke? 100 times?

@ 2000hz, sampling 100 times per stroke = 5ms per sampling time

I have nothing to compare that time to, but it doesnt seem like a hard job for a small cheapo computer to handle.

Thieroff
11-19-2006, 07:17 PM
TC Sounds has introduced a *passive* answer to this solution by designing the voice coil around the BL curve (varied amount of windings)...why hasnt this been done on midranges?

I believe that winding these type of VCs is time consuming and complicated, also it is more difficult on impedance options. (DVC and such)

Also, a simple midrange doesn't have much throw, a common mid has like 3-4 mm of excursion, compared to the 30+mm of the subs with such VC windings

There's less of a chance of non-linearity with so little throw

Keep in mind this is a new technology also


CT

thadman
11-19-2006, 07:36 PM
Even though midrange drivers have much less throw they are still subject to uneven BL curves. If I recall correctly, Xmax=71% of Bl strength...regardless of how long the stroke is. These designs are still subject to the same detrimental effects of having much less Bl strength at the extremes of their excursion.

thadman
11-19-2006, 07:40 PM
I believe that winding these type of VCs is time consuming and complicated, also it is more difficult on impedance options. (DVC and such)
CT

Scanspeak charges $410 + shipping for a pair of 7" revelators and $796 + s/h for a pair of R2904/7000 ring radiator tweeters. I certainly dont think winding the VC differently would contribute a lot to the cost of these drivers, most of the cost of these drivers is derived from R&D.

thylantyr
11-20-2006, 12:36 PM
Random

1. Who wants to pay huge dollars for a special midrange with dedicted
servo amplifier ? I'm sure someone will, but not me. Take a $50 mid,
design special electronics {more $$$}, design a special amplifier {more $$$}
and you have to sell all this as one complete package. Is there a market for this?
You can probably build a company around this idea and sell it to dumb consumers
regardless if it works or not. lol

2. There are low distortion, high quality midrange drivers on the market with without servo, and it's much cheaper plus you can connect it to any amplifier of
your choosing. Win win situation.

3. Quality midrange drivers {not midwoofers} only have a few mm of linear stroke, cone excursion is low as you play higher frequencies. If cone excursion is low, then the quality rises by default. You can get low distortion sound out of
cheap drivers by operating them at reduced output. Look at headphone drivers,
ultra cheap, high quality sound at certain SPL levels.

4. Line array solutions are probably a better solution to getting low distortion midrange output. Take a cheap midrange, it has the potential for high quality
sound if you operate it at reduced SPL. Take 20 cheap midrange, operate the
array at the SPL of the single driver and distortion is reduced by 1/20 and you
hardly did any work to get low distortion. Depending on design and wiring,
you can boost overal SPL levels to high levels keep great sound.

joetama
11-20-2006, 10:14 PM
Surround less mids have very very little excursion. So there really would be no need for it to be servo driven. ;)