And another post of note. FWIW, I found both of these to be quite revealing and helped me answer my questions above, so pasting them here for others to easily find seemed like the right thing to do.
"Bozak Midrange and General Sound
Well, here I am starting at the beginning of time. (Well, April.)
Regarding the comments about "The Bozak Sound:" The early Bozaks ('50s) were never an easy first sale. I worked as the repair tech in a prominent stereo store in the '50s (yes, I was barely out of diapers) and saw this first hand: In A-B comparisons in the listening room, most first-time buyers would opt for a competing system that had more flash bang in the sound. The Bozaks are just too true, while the competing iron jumped at you. Bozak was under a lot of pressure from the dealer network to make the Bozaks sound more like the inferior competition which was selling better. Most first-time buyers, after learning how little they liked hearing the same flash and bang in everything they played, would come back to the store in a few months and say, "Uh...could I hear those Bozaks again?" But this was little consolation to the dealers, who wanted Bozak to compete for first-time sales.
The early Bozak systems were perfectly balanced - woofer to midrange to tweeters - and everything in phase. So in the early '60s, when the aluminum-coned B-209A/B midrange and B-200Y tweets came on stream, Bozak really fouled up the xovers. For starters, the polarity of the midrange was reversed. This resulted in a mid sound that was incredibly prominent without actually being louder. With the mid reversed in polarity compared with the woofs and tweets, the xover regions were cancellation notches. This 'isolated' the midrange in a manner similar to a picture which is surrounded by a wide, plain matte - it makes the subject more prominent. But the down sides were degraded overall smoothness and seriously degraded stereo imaging. Without any doubt, the reversed polarity on all Bozak N-10102A xovers should be corrected. (It is not crossed on the N-10102 xover, used with the early paper-coned B-209 midrange and B-200X tweets.
The other issue was the Y tweets. They are about 9 dB hotter (louder) than the woofer and midrange (and the previous paper-coned X tweets). Presumably this was to enable inclusion of a Brightness control which could reduce tweeter level or make it higher than flat. Only a very few systems actually had the Brightness control, mainly the early Symphonies and a few B-302A systems. After just a year or so, the Brightness control pots were eliminated. A simple network consisting of a 25 ohm resistor paralleled by a 2.0 uF capacitor was put in series with the Y tweets. The results, by today's standards, are pretty awful. It results in a big hump in the mid highs, 5.0 kHz to 10.0 klHz, allowing the natural rolloff of the Y tweet above 10 kHz to go unaided. Can you say, "Disco?"
It is not my job to help Bozak sell speakers in a tough '60s and '70s market. What I am doing is re-engineering the xovers to remove the strange tweaks and allow the world-class drivers to sing in their full, true voices, unhampered by the craziness of the '60s and '70s. To that end I designed a much better circuit to drive the Y tweeters. It is more complex than the bozak one, and works much better. It reduces the extra 9 dB level to match that of the woofs and midrange, flat, without the hump. Then, with 9 dB of 'extra' level to play with, it is used to extend the extreme high range, boosting from 10 kHz up to the tweeter's normal limit of about 16 kHz. The result is highs that are very smooth; no peaks, no dips, and a smoothly extended upper range.
(The later xovers, from about '95, need even more help.)
You wanna know what the punch line is to this: Dig: No one who has never heard their Bozaks with the '60s ~ '70s craziness exorcised, has any idea how great they can really sound! That sounds radical, but is very, very true.
When the corrections are made, here is what you get, echoing Tony's comments:
The TRUE Bozak sound is neither mellow nor sharp. It is just incredibly accurate. Let me magnify that point. Little-known fact: The B-209B midrange driver uses the same 'motor' as the 12" woofer! Same magnet, same post and plates, same voice coil diameter. Yet the ultra-light aluminum cone must cover a range of only about 2-1/2 octaves (with 400 Hz lower xover). Driving that with the woofer motor is a little like putting a hemi V8 in a VW. The B-209B, with enough driving power, will reproduce transients that many other mids don't even see.
The woofer cone doesn't look particularly light, but the entire cone assy., including voice coil and vc tube, inner 'spider' suspension and outer suspension, all together weigh 39.5 grams. That translates, again, to superb transient response. The gutty string sound of a well-recorded bass can be so enjoyable on a Bozak woofer.
Here's another important point. Quick transients in good-quality recorded audio can easily reach 10 dB (voltage) above average level. That's a factor of 20:1 in terms of power. Therefore, if your average level is 3 watts, the amplifier must be capable of a clean 60 watts if all the transients are to be heard without clipping. Sometimes it is said that Bozaks will play comfortably loud from a pair of 6AQ5s or the like - call it 15 watts. It is highly unfortunate when that is done, because few high transients are being heard.
Rudy Bozak, in his many tutorial writings in brochures over the years, spoke about the 'educated listener.' It is clear what he means: those who have never heard Bozaks, properly configured and with adequate driving power, literally don't know what they are missing. They are judging from their experience base of speakers of less capability.
Bozaks do have a sound character, and this is it: Properly set-up Bozaks reproduce, accurately, every kind of sound you can throw at them. They are great on classical, great on jazz and great on rock. And they don't give a hoot what is driving them - VT or SS - so long as the power is ample and very clean. There is nothing to support the opinion that Bozaks are best with VT amplifiers. I listened to my early mono systems with an MC-30 for years. When I converted to stereo I went with a clean SS receiver and have never looked back. Actually, the damping factor of the Macs is very moderate - around 12 - very kind to cranky, hard-to-drive complex xovers. The Bozak bottom end actually appreciates the much-higher DF of good SS amplifiers.
I have unlimited admiration for the late Rudy Bozak. Nothing I do is intended to 'correct' any of Rudy's work. Were it not for the intense pressure from the dealer network, I am fully confident that the sound with my mods is exactly the sound Rudy would have liked. It took the speaker industry years, even decades to adopt some of the principles Rudy originated in the 50's. My work is dedicated to Rudy Bozak, in hopes that modern listeners can hear his genius through his world-class drivers as they were designed to be heard.
There's lots more to say - about enclosures, bi-amping, tweeters a lot. This essay will serve as foundation on which to base any further (hopefully brief!) comments.
With best wishes to all,
Pat Tobin"
