What is the difference between Symmetry Conga Drumheads and the older 'brown trim' Crimplock Conga Drumheads?
Symmetry is an improvement on the older Crimplock construction.
Crimplock refers to the aluminum flesh-hoop crimped over the film that seats inside the channel (of the flesh-hoop) with glue.
The Symmetry type is the addition of symmetrical folds around the collar that conform to the bearing edge as you tension so it's easier on your hands and provides increased projection (better contact between head and drum), tunability (how the film stretches and seats), and durability (as the head conforms, there's more tension on the collar and less stress directly on the flesh-hoop).
Thank you this was informative........