JBL began "bypassing" the mylar and non-polarized electrolytic capacitors in their frequency dividing networks beginning with the model L110A loudspeaker system. These bypass capacitors were smaller, higher quality polypropylene and polystyrene capacitors which exhibited greater linearity, spaciousness, and dynamics.
Our Library contains numerous documents and brochures with references to this practice. For example:
Page 3 - 1982 Loudspeaker Systems Catalog
Page 2 and 3 - JBL L250 & B460
Page 7 - JBL DD55000 Everest