AR-4x Inductor and Stuffing Changes

[johnieo]

Roy C. and I have been comparing notes on AR-4x details. It would appear that early AR-4x, say before about serial 290,xxx (mid-to-late 1969), used AR-#4 inductor (0.88 mH) and contained 17 oz fiberglass stuffing. The later AR-4x used AR-#5 inductor (1.2 mH) and 11 oz of fiberglass stuffing.

It would appear that the AR-4x went through an itteration that, in principal, was the same as reported previously for the AR-3a in two separate posts (#5886 and #5322) where it was noted that the fiberglass stuffing was reduced from 28 oz to 20 oz and the woofer inductance was increased from 1.9 mH (AR-#7) to 2.85 mH (AR-#9).

These changes would increase Qtc. The AR-1 was designed with Qtc = 1. The AR-12 had Qtc = 1.15. Perhaps Qtc was increased in AR-4x and AR-3a long before the 1977 arrival of the AR-12???

On a similar note, three of the woofer inductors found in my older AR-4x speakers were labeled "2ax." These coils all measure 0.88 mH (e.g. AR-#4 coil). I've never seen an AR-2ax, but E-bay photos of their crossovers clearly show a "7" stamped on the coil (1.9 mH).