View Single Post
  #12   Report Post  
Posted to rec.audio.high-end
Peter Wieck[_2_] Peter Wieck[_2_] is offline
external usenet poster
 
Posts: 137
Default Motional feedback in speakers

Ummmmmm.....

A speaker is a linear motor with a magnet, and a commutator (voice coil). Just as in a PM Motor, when current is applied, the motor spins. DC motors spin according to the polarity of the power applied. Speakers move in or out depending on the polarity of the current applied. And, PM motors do, also, have a fixed resistance across the commutator just like a voice coil.

Now, when current stops being applied, the motor generates current - acts as a generator as it spins down. If it is unloaded, that current goes nowhere and does not add additional resistance to the motor spinning than normal bearing friction. However, if the motor is loaded, there will be additional friction.

Similarly the (conventional) speaker. Try it some time with a sensitive VOM.. The bigger the driver, the more easily this is observed. Just a few taps on the speaker cone will show you.

All and at the same time, DF is only one (1) single factor in how amplifiers interact with speakers. And, today in 2019, the issues that drove speaker design in the era after field-coil speakers were dominant up until the development of acoustic suspension are not particularly relevant as much evolution is taken for granted (and usually is granted). However, as one who spends as much time with electronics from the 1930s as from the the 1970s and up, I see all sorts of variations on how to control large speaker overshoot, sagging, and similar problems. A 15" Zenith speaker driven by a single-ended 6F6 is an entirely different animal than a 12" Long-throw woofer from an AR3a.

Peter Wieck
Melrose Park, PA