Driver Condition Assessment

[Mazeppa]

Replies from John at MSound to my queries about how to assess whether a cone type driver is worth repairing or not, whether reconing is appropriate. Offered as an aid to DIY types, my only affifliation with John is that of a customer that has bought one refoaming kit from him. He has given his permission for reprinting in our forum.

Generally, mechanical damage is "visually" obvious, or can be felt by carefully moving the cone in and out and listening for scratching sounds that will indicate shifted magnets, broken or bottomed out or burnt coils.

For electrical damage, a meter is needed to tell you whether the voice-coil is bad... IF the coil reads open (infinitely hi on the meter), then you have a blown out coil. Sometimes you will still get something close to what it "should" be... typically 3.2 (or so) for a 4 ohm coil or around 6.5 (or so) ohms for an 8 ohm coil, but IF it sounds scratchy It's still bad! Then this calls for a recone.

Some other easy checks you might try doing as a step towards considering refoaming anyway: Take a strip of your thicker shimstock and "sweep" the voice-coil cap. IF it does not feel clean and clear, you know you have problems. Remember, this is the "inside" of the former and NOT the wire side... so IF this side feels "lumpy" then the voice-coil has definitely taken some heat! Again, you may HEAR some crunchy sounds with this problem.

OR If you feel galling (where a round former isn't round at the bottom anymore, where the edge has flattened out) or catches at the bottom of the former (note that the former should be UP about a 1/4" from the extreme bottom of gap) and within the reach of your shims, so IF you feel "galling" either the former has bottomed out from too much power (common with the soft formers found on Infinities), or worse... IF your shims get stuck on one side, perhaps you have a shifted magnet assembly which will call for major work; this kind of speaker is pretty much a major loser unless it is a extremely high dollar driver that has a special customer that is willing to shell out whatever it costs to fix it!

ML.John

McPeak Sound Co.

msound@citlink.net