AR-3 speaker woofers

[Guest]

I have a pair of AR-3a woofers that have round magnets and also a pair that have square magnets. My question is: did AR make both types and is there a difference between the two? Is anyone familiar with the two types?

I know that there is a difference between the AR-3 and the AR-3a woofer magnets, can someone tell me the differences there also?

[tysontom]

There are several variations in the woofers used in the AR-3a, but all used the 10-11 lb. magnet assembly (54-oz. magnet). The first AR-3a, introduced in 1967, used the AR-3 Alnico woofer with cast-aluminum frame, so there are several thousand of those still out there. In late 1968 or early 1969, AR introduced the ferrite-magnet woofer (stamped frame) to the AR-3a, and these woofers proved smoother than the AR-3 woofer with its damping rings. Both woofers have extremely low distortion, even by today's standards. Some of the ferrite-magnet woofers had perfectly round magets; some had oval slots around the periphery; some others had square magnets. It depended on the source of the magnets at the time. All had the same parameters, which essentially was a 17-19 Hz. free-air resonance (fs); and when mounted in the AR-3 or AR-3a cabinet, resulted in a system resonance (fc) of 43 Hz.

--Tom Tyson