Motional feedback subwoofer HELP

[Johanson]

I have been sold a diy built Motional feedback subwoofer that is distorting, plus lots of lose screws, HELP I think i've been conned, so its money back I hope. On the dual coil visaton drivers there is only the normal cable run to the terminals. Should there be another cable run from one of the dual coil drivers for the sensor to feed back to the amp or don't it work that way. THANKS CHAPS

[subwo1]

Being on my favorite subject, I would like to take a go at an answer though motional feedback is a little exotic even for me at this time. A quick reply could be that some subwoofer drive circuits could try to monitor the inductance of the voice coil. Actually, I don't know if doing so is even possible, but maybe theoretically since the inductance maxes out when the coil is at bottom and minimizes at the top of its excursion. I would expect any difference to be small, however, until the coil begins to leave the magnetized core. Others may be able to elucidate on this matter. There may be other ways to estimate cone position without direct positional feedback.

[BlackWidowAudio]

You are right in expecting another connection to the driver.

Electronics & Wireless World published an article, detailing the construction of a motion feedback sub, I think in 97/98, I have the article somewhere.

In this aritcle the Driver was a dual voice coil driver, which used one coil to drive the driver and the other for rate feedback, which i think was then put thru an integrator, to provide the feedback.

Anyway that is all i can remember. I will look for the article, if you want it email me. I will try and get you a copy.

Dan

[BlackWidowAudio]

I just found the article, it was published in Feb 1997.

Dan