Voice coil gap tightness

[breez]

How tight is the voice coil gap in common subwoofer drivers? I have a Peerless Resolution 15" driver and during break-in I may have accidentally overheated the voice coil.

This was a while back, but there must have been more than 100W rms power wasted as heat in the driver. Excursion was very high, but there were definitely no noises during the first few hours. Over the night a distinct *clip* sound developed. Pushing the cone in and out the coil rubbed a little depending how I pushed the cone. After cooling for several hours it didn't rub anymore unless I deliberately pushed the cone off-center.

Do you think the voice coil could be damaged a little? I presume it is normal for the voice coil to rub if cone is pushed the wrong way, but I can't remember how it was new.

 

[HK26147]

The gap is not very big, last recone kit I got came with shims, thicker than paper, approximately the thickness of card stock.
IMO You should not hear a rub at all if worked within normal limits.
I suspect an overheated and warped voice coil.

 

[Iain McNeill]

What I've seen happen is the laquer used to glue the VC windings together boils and bubbles forming a high spot. In particularly bad cases, the windings themselves can shift slightly. Clearances are in the order of 0.25mm so it's easy to have rub problems.

You can't fix this through the dust cap as the coil is on the other side of the former. Some manual cone abuse might work, especially if you're resigned to reconing.

 

[breez]

Looks like I just have to see how it works in a box and compare to a new one I ordered (plan is to build two boxes).

 

[breez]

Ok, the new one rubs too if pushed off-center. I guess the broken-in one is good to go. I'll see in a few months time when I'll get to building the boxes.