RCA Model 501S1 Hi Fi BiAxial 12 inch Speaker,

This driver is from the estate of an RCA engineer and collector.  

This speaker is one of a series that RCA produced without the ubiquitous 'MI' part number prefix.  The 501S1, 502S1, 503S1 and 500S1 were introduced in 1955, with the 501S1 being the only model that had 2 drivers assembled in a single assembly.  

The 501S1 has a 12" paper cone woofer with a 1" VC, and a 3" driver with a 9/16" VC.  The tweeter is attached off axis with a 3 point mount that bolts onto the woofer frame.  There is a 4uf electrolytic crossover capacitor mounted under the rear cover. 

The specifications for the RCA model 500S1 High Frequency driver match those for the tweeter used in this BiAxial combination.  The primary difference being that the 500S1 was sold separately with a enclosing rear chamber.  All of the other specs are the same.

These drivers used AlNiCo "High Sensitivity" V magnets. 

The speaker, frame and cone are all in good condition, with no damage to the either cone surface.  There is a thin foam ring that runs around the circumference of the cone, just inside of the accordion crease.  The foam is deteriorating from age.  

There is a keyed 3 pin plug that fits into a connector mounted to the frame of the woofer.  Both the plug and jack are in good condition.

The manufacturer/date code under the magnet cover is 274 741, which dates this speaker at week 47 of 1957.

Specs:

Response: 40 to 18,000 cps 

Power Handling: 12 watts

Impedance at 400 cps 8Ω

Magnet weights; 14.5 oz, 1.47 oz.

Resonant Freq: 65 +/- 10 cycles