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In the Forum: Playback Listening
In the Thread: Some Observations about Science and Bass
Post Subject: Negative FeedbackPosted by Vasyachkin on: 7/19/2010
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 Paul S wrote:
I do not know and so could not even guess if the "silicon" or the driver itself would be the weaker link in producing ULF these days.  So I am fishing to see what any readers know about ULF in general and "contemporary" servo ULF in particular. If the accelerometer is not designed for music, what, if not a feedback loop, controls the long stroke of a ULF driver powered with a big AB amp or, more likely, a D or H amp?  Isn't this in the end mostly a less-efficient way of attempting the same thing, ie, "control" of the woofer via its motor?
there isn't necessarily a need to control anything electrically here.  control with respect to subwoofers refers to control of box resonance which can be accomplished mechanically with a resistive box vent.


it is possible to also have amplifiers without negative feedback you know.  as a matter of fact i invented one such amplifier but years later learned that it had already been implemented.  an amplifier using a transformer as a voltage gain element is inherently linear and requires no correction.  


negative feedback is only needed to correct errors.  but it is possible to design a system without errors in the first place.  TC Sounds LMS subwoofer for the most part is such a driver - its error without any accelerometers is at about the same 2% as for Velodyne WITH accelerometer.  


question is - what sounds worse - 2% distortion from a driver or 2% distortion from an accelerometer ?  accelerometer is essentially a piezo tweeter wired in reverse, so Velodyne is essentially a piezo subwoofer LOL.  


well, actually there can be different accelerometer technologies - it can be capacitive as well, but even so the "suspension" is still made out of silicon and crystals aren't known for being very linear when it comes to deformation.

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