N_Cook wrote:

Due to dirt in use or at manufacture?
Carlsboro 10 inch ,open circuit, so burrowed in to explore. On the phenolic
cylinder that is the former for the voice coil . 4 pairs of scored
ines( stand out white against the amber colour of the phenolic). Each pair
about 6 to 7mm apart and arranged pairwise diametrically.

I suspect 4 pieces of sharp edged metal shim used in the original cone
setting and scored on removal. All the lines go axially , fully from one end
to the other , so if made in use would require the diaphragm (spider?) being
driven 10 mm into the magnet housing. Apart from the nearly symetrical
distribution of the lines.

How much time do you waste inflating customers' bills by wasting time on the
pointless ?

Graham