Monday, December 28, 2020

Fixing Home Speaker

 I have a set of Polk Monitor series speakers from the late 1980's.  These are fantastic speakers in my opinion, even now.  However, in one of the speakers (each has 2 drivers) both drivers started crackling very bad.  Upon inspection I found the coils dragging on the magnets.  The drivers in the other speaker were fine.  You can hear the dragging when you press in on the passive bass radiator which pushes the drivers out.  

I looked into these drivers with are part number MW 6503 and have been discontinued.  There are copies available for $35 to $70 range each.

I experimented with pressing on the cone in various places to find a place where it would not drag.  It seemed to be an alignment issue.  Maybe they creped a bit over time? I decided I would try to align them back.  Nothing to lose here right?  Either I fix them or I needed to replace them anyway.  I took a piece of plywood and a vise and began carefully pinching an edge of the magnet where the dragging was gone.  This basically bends the driver frame a bit to realign the coil with the magnet.  To my amazement it actually worked.  Here is the after video.
This is tricky to get right.  The metal has significant spring back and you want to bend in small increments. You have to carefully get it to yield just a bit at a time and retest.