There are so many ways this project can go wrong. The Bozak system is a logical fallacy for new owners who simply want to replace a few caps and get them into daily drivers.
I know Biggles is aware of this, but others may not be.
If we look at the history this more or less makes sense. Bozak sold an upgradeable
system, more or less, not speakers. The standard, as opposed to custom solutions or those created by third-party integrators, had single woofer, dual woofer, and the top of the line was quad woofers. One could purchase a variety of lower-cost two-way system (single or dual woofer with tweeters dragged into service as midranges) and add a midrange at a later point.
Being a small company, Bozak—this is an inference from its actions—did not want to maintain a multiplicity of drivers or crossovers. Since an 8 Ω quad could be built with four 8 Ω drivers (series to yield 16 Ω, then parallel to yield 8 Ω) this system could use the same 8 Ω crossover as the single driver one. The early dual woofer systems required putting two 8 Ω drivers in series to yield 16 Ω. (Later units used special 16 Ω woofers run in parallel.) But that meant a 16 Ω midrange was required, so from early on the midranges had both impedance. (The 16 Ω woofers are uncommon, as they were only used in the dual woofer configurations, or special 16 Ω quad configurations made by third-party integrators.)
So now two different crossover were needed: one for the 8 Ω systems and one for the 16 Ω systems. The multiplicity of early crossovers—N-101, N-102, N-103, N-104—were folded together into a single unit, the N-10102 (it is both an N-101 and an N-102, but it can also serve as an N-103 and N-104), which then used different taps on the inductors and then different taps on a capacitor bank. Very clever! A common set of parts could be sourced, a single crossover built, and all the magic would use taps. Later crossovers were hardwired and re-used the early numbers, but were essentially limited versions of the N-10102 which covered up the inductor taps with tape (I've unwrapped them to verify this) or used specific capacitor values without taps. This is why stickers were used to number those crossovers instead of silkscreening.
But then we come in fifty years after the development of the N-10102 swiss-army knife crossover and start tinkering with it. Oh, we say, we can use a 16 Ω tap to move the 8 Ω crossover point down. We can junk the capacitor bank in favor of fixed values, since we're building a specific speaker. And we can fix the polarity on a forward midrange. While we're at it, let's balance the tweeter with an attenuator and tame its impedance hump at resonance using a Zobel. And then there's a flowerpot midrange bell, which extends functionality in a way that only existed on the top of the line units.
So at this point we've built a new and more complex crossover using parts we had or ordered, and we've reconfigured the speaker as a whole. And that's where the trouble comes in.
Bozak gives us the freedom to do this upgrade, but if one doesn't have a background in loudspeakers and crossovers it can be difficult to get it all right. It isn't as cookbook as it would be with a kit from Heathkit, EICO, or Dynaco. Tobin was perhaps too close to the problem, in that he didn't really explain what he was doing. Perhaps because the people who were rebuilding the crossovers either were techs who understood the issue, perhaps because owners who didn't want to understand the math, they just wanted a cookbook solution, or perhaps because he was dealing with a small group of people and nobody ever asked for details. Either they did it themselves or paid him to do it.
I know that when I've explained the math behind the choices, and why one can't just drop a 16 Ω midrange into an 8 Ω system, I usually hear crickets chirping and frogs croaking.
So Bozak was never intended to be a modular system for non-integrators and those building new speakers from scratch, as we are. That's why so much discussion exists on the purpose for each of these modifications and their realization. This problem was created when people use Bozaks as a kit without realizing that there isn't much of an instruction manual. I suppose I should write one up incorporating the knowledge base and some diagrams.
