i have the drivers and horns to make up a pair of these. the 909s diaphragms are 26420 pascalites. they look new.
This could be my next Altec build soon as i get moved into N Florida.
The secret to success will be finding the data to successfully clone the 630hz high power handling crossover, it's got some special shelving and HF protection.

I'd go here and save ALL images if you;re serious about the build: ALTEC LANSING M500 crossover - MES ENCEINTES ACOUSTIQUES

I don't think you'll find that info anywhere else.

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