Merely a curiosity question. Exactly how lo fi are the JBL phenolic compression driver diaphragms? How much improvement did materials that wear out bring? I have thought about this because I am so over the care and feeding of foam surrounds since non self-destructive materials, if designed for the transducer, are performing well in modern speakers.

Since systems using pieces like the 2470 usually allowed for a tweeter, extending the frequency response with metal diaphragms is not considered by me to be an improvement.