Rectilinear 3's: Is it worth upgrading tweeters???

Jameswei hits the nail on the head with his analysis. Mine too came new with the whizzer cones.

I want to thank every one for their informative posts about the Rectilinear 3's. It is always fun to hear about these old "classics" of the audio business. Regards, SJ

My recollection is that the shorter version were called the "Lowboys", and did not sound as good. I had a pair of the original III's for years, and my parents still use them, though now as their surround sound speakers. They always reminded me of a poor man's KLH 9, with the emphasis on high-end clarity versus depth, or presence. They had more detail than the Advents, from which I had moved up, and were not as biting as the JBL's. And unlike the KLH 9's, one did not need either a sub woofer, or a second pair to hear base. However, compared to the KLH 9's they sounded like a cloth was covering the speaker. Still, for their day they were special, and could handle virtually any type of music. I could play "Shaft", louder, and clearer than my friends, which seemed like a big deal at the time. They also absorbed more power than many other speakers of that era. My parents also had my old pair of Advents, and those gave out a while ago. Wow. You uncorked years of musical memories.

Many years after the original posts, I can say yes, it is worth upgrading the tweeters. I got my pair of Rec III highboys in 1975 from a grad student in Engineering Acoustics at Penn State. We went into one leg of the tweeter sets (there are two legs, each with 2 tweeters), put in an 8 Ohm resistor in place of the larger tweeter, and put a Phillips-Norelco 3/4 inch soft dome in place of the smaller tweeter on the top. This improved imaging and high end considerably, verified both by ear and in an anacholic chamber. 

The original midrange is also a Phillips-Norelco, contained unit, with a whizzer cone. One of those had blown out, and back in the day, McKee made a respectable replacement. Only now 2018, am I really looking for replacement speakers. They are just a bit tired. 

The Rec III was the first scientifically designed speaker, solved properly as a 6th order Butterworth box. These days, there are better solutions, but I've been reluctant to spend money on speakers that sound only a little better. Note that I have a large listening room, and many good sounding modern speakers do not move air like the big woofers and bass-reflex port.