Bozak custom built 3 ways any good

[RonaldP]

I just picked up a pair of Bozak speakers at a estate sale. Kinda pulled the trigger quick I put in what I thought was a low offer of $400 at the end of the sale. There three ways in custom built cabinet with the B199Bc woofer, B209BC mids and 2 array tweeters in front of the woofers. The crossover is N104B with some nice poly caps in there but one had a open tweeter cap. They sounded OK on initial demo at home so a simple refresh of tweeter caps and internal wiring with parts on order has begun. Any comments on what I have? My initial thoughts are I wish I had more drivers like some of there bigger models but the parts I have appear to be quality. This will be hooking up to a Pioneer SX1250 that has HPM100s right now.

 

[soundmig]

Any pictures? Bozak drivers are usually quite good, so you probably have a good value there. There are some Bozak experts on AK, so with pictures you can probably get some excellent information.

 

[drbiggles]

Hey Ronald!

You did drag some some excellent drivers and crossover there pally boy. I hear great things about your ceramic B199 woofers, I'd love to try a pair out myself.

We need pictures, plain and simple. I need measurements from the inside of your cabinet, height, width and length. We need to find out your internal volume to see what we're playing with and what to expect in bass response. We need close-up pictures of your crossovers to see what's going on. We need to know if your tweeter's cone and dust cap are completely black, or do the dust caps of the tweeters shiny chrome?

With the crossovers properly updated and configured and a chamber that covers the back of the midrange, you're going to have a world class pair of speakers. The detail in bass and mid-bass notes are going to cause you to shed a tear.

Fill us in with the information and we can get the ball rolling!

Biggles

 

[RonaldP]

Here are some pictures and requested information. I already started to rewire the crossovers with some 18 GA silver coated military spec wire and bought a new replacement pair of capacitors for the tweeters from Parts Express. Its OK if I need to reconsider were to take things as I can stat over. The inside cabinet height = 26.6 Inches, Width 17.5 Inches, Length 16.6 Inches. The crossover caps are 22uf 63v 2 in parallel for mids and 5uf 63v for the tweeters in there now.

 

[twiiii]

You need to join the Bozak owners website and pull up diagrams to see which version of the N104 you have. You night want to add the Tobin mod to the tweeter section of the crossover and preform the 1250 HZ option to the 209 mid range. Its all explained in detail on the website. Your crossover to the woofer has already been changed from 800 down to the preferred 400 HZ like the larger systems. I would recommend removing the tweeters from the front of the woofers and place them as near to the midrange as possible in vertical alignment taking the splay out between the tweeters. I don't see the factory RC network for the tweeters so they should be pretty bright in this configuration. You need to check which version of the 200 tweeter you have. If you have the Z version its a totally different animal than the much more prolific YC version that can use the T mod which the Z version does not need.

 

[RonaldP]

The tweeters are Model B 200Zc 4 Ohms. So the tweeters need to be moved up and mounted flat in vertical array similar to the larger speaker lines. I need to digest all these crossover mods recommendations.

 

[drbiggles]

We need to find @Retrovert, he'll have valid suggestions for the crossovers. Your cabinet volume comes in at 4.47 cubic feet. That's darned close to the recommended 5 cubic feet. Twiiii says your crossover has already crossed the woofer at 400Hz, so that's good. But it means that you now need to put a little enclosure over the back of the midrange so the backwaves from the woofer don't mess with it. You've got great tweeters, so they should be good go.

Does your enclosure have insulation/batting on the sides, top/bottom and back? Would it be possible to get pictures of the exterior of your cabinets, just for fun? I'd like to see!

Here is the enclosure I built for my B209B midrange drivers. It's going to want to be 452 cubic inches total internal volume. I used a cardboard concrete forming tube I bought from a local hardware store. It's an 8" tube that I cut 9" deep. I got this information from the Facebook Bozak users group.

Biggles

 

[bshorey]

The tweeters are Model B 200Zc 4 Ohms. So the tweeters need to be moved up and mounted flat in vertical array similar to the larger speaker lines. I need to digest all these crossover mods recommendations.

I'd second the recommendation to build a subenclosure for the midrange. It made a world of difference on mine. As you have a custom cab, I'd also move the tweeters as suggested. Personally I'm still on the fence wrt the Tobin mods, I went that route and ended up disconnecting the 7.5 ohm resistor as it really killed the highs. With that one change to the Tobin circuit, and the subenclosure for the mids, they sound very nice.

bs

 

[RonaldP]

Attached are pictures of the cabinets inside and out. There very quality build like dove tail joints every were with plywood, hardwoods, and veneers. The front grill is plywood with cloth.

 

[Retrovert]

The N-104B is a mid-1970s crossover with ferrite cores. The N-104 is just an N-103 plus the N-25 capacitor bank.

At some point in the 1970s Bozak switched to ferrite-core inductors to save money. (Believe me, friends, for I have seen this abomination with my own eyes, and lived to tell thee of it. I lost my senses and ran screaming from that place, and the horror has never fully left me since that day.) These crossovers were otherwise typical Bozak N-104 crossovers, just with a ferrite plug in the woofer inductor. (I passed on them, and sometimes at night I shiver at the non-linear crossover saturation horror narrowly avoided, in that place with no right angles and horrible phantasms always at the corner of my eyes.*)

It may, alas, use inductors made from aluminum wire with crimped on connectors, since aluminum is difficult to solder. That's why the aluminum wires have lugs instead of being soldered. As with aluminum houshold wiring, the oxide layer often builds up creating a higher impedance path that has non-linear properties. Yes, it has a a copper color but that may be the varnish insulation. I'm not certain as they're not in front of me and the photo isn't large enough to tell what's going on at the crimp.

Note: I specifically used impedance here, not resistance, because the resistance is frequency dependent. which means it is impedance Metal oxides form peculiar rectifiers. This is the basis of the radio receiver using a rusty razor blade and the rectifiers made from copper oxide and selenium oxide.

Back to the ferrite core. Ferrite has non-linear properties and the differences are audible by those without Ye Magickal Golden Eares. So I would replace the ferrite-core inductor. and the other one, too, if it is aluminum wire, with good old-fashioned copper. Let's all sing along: Gimme that old time, copper, gimme that old time copper, it was good enough for Rudy, it's good enough for me!

* The Horror that Came to Bozak, by H. P. Lovecraft (1928)

 

[Retrovert]

Here are the volume calculations explaining the size of the midrange bell (well, tube):

audiokarma.org/forums/index.php?threads/tobins-104t-crossover-not-living-up-to-the-hoopla-a-solution.736070/page-2#post-9966880
​

I did the math on that once, no sense doing it again.

 

[drbiggles]

Wow, and congratulations. To answer your first question, yes you got a great pair of speakers. Not only great looking, but the drivers will backup the looks with great performance. That ceramic B199 woofer will give you some really good slam with enough detail to really impress. The midrange is so full and lush, a wonderful experience.

I see Retrovert stepped up to the plate! You're going to want to build the Bozak N10102 3-way crossovers to Pat Tobin's design. You don't have to do this today, or tomorrow, but this is a necessary addition.

Congratulations!

Biggles

 

[Retrovert]

The midrange polarity may be reversed in these. This is one of the perennial arguments. Here's what I've elsewhere posted about that.

The Tobin mod undoes the reversed midrange.

First, the rationale from Bob Betts, Rudy Bozak's right-hand man and the co-designer of the famed Bozak 909/919 preamp and 929/939 amps among others:

www.bobsamerica.com/bozak-xoveranalysis.html
After much analysis, testing, and evaluation we made the decision to accept the phase shifts at the center of the midrange band, rather than at both ends of the midrange band. We then sat back and waited for the fireworks to begin. Oddly enough, there were amazingly few! This is surprising, since customers are usually very quick to express a complaint, but remain conspicuously quiet when content. The feedback from our dealers, reps and end-users was almost unanimously complimentary. One Sunday morning I received a phone call from Benny Goodman asking when I was going to come to his studio and "...make the new repairs that I heard at the factory?"This is not a "yes" or "no" or good or bad decision. It is a gray area of engineering that is associated with the subjectivity of how we listen, what we listen for, our personal tastes, our ear-to-brain calibration from live vs. reproduced experiences (or lack thereof), and the intuitive thought process. The condition (and dilemma) of where to place the phase incoherency is a trade off - neither is technically correct when applied to a passive crossover, but quite often, the intuitive thoughts of a semi-technical evaluator will weigh in favor of the in-phase condition, only because "it seems to make sense." Oddly enough, Bozak Inc. was one of the last manufacturers to effect the midrange phase reversal. At that time, according to our research of currently available 3-way speaker products, about 85% to 90% of the speaker industry had already made the "correction" changeover.

Tobin's commentary:

forums.stevehoffman.tv/threads/tobin-mods-to-bozak-302a-urban-speakers-definitely-worth-it.75950/page-2
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.

Betts also has an observation about transient response:

www.bobsamerica.com/bozak-xoveranalysis.html
If a speaker sounds like the sound is coming from inside the box, then it probably has poor transient capability, and if it sounds dull and lifeless, then the damping qualities are probably not very good. Here’s a standard test that engineers have used over the years: Play a known (to you), small jazz combo of acoustical (not electronic) instruments and listen to the bass drum and string bass. Are they separate and distinct? Or is the woofer just flopping around in rhythm to the beat? Bass is bass, but what is it that makes up the bass—can you tell by listening? So this is basically why two loudspeakers with similar “published” specifications can sound so vastly different. It would seem that no one ever offers specifications on IM, harmonic, and phase distortions. In my 40-plus years as an audio products design engineer, it has never ceased to amaze me how audio manufacturers perpetuate the virtues of “flatness”—linearity—without even so much as a mention of other physics characteristics. Over the years, amplifier producers have been forced, by public demand, to publish such numbers as intermodulation distortion, harmonic distortion, damping factor, etc. But remember that these figures are gleaned, gathered and garnered on a test bench using sine waves as audio signals and resistors, not loudspeakers, as loads. Seldom will you hear any discussions concerning “dynamic stability” or “transient reproduction.” Likewise, the loudspeaker industry suffers similar, if not worse, negative virtues.

 

[RonaldP]

Bummer I thought I had all the right parts. I just looked at the crimps and its aluminum wire as Retrovert stated. Now what?

Sound like they need to go and I'm not even sure what values they are or details I need to consider on a upgrade.

 

[Retrovert]

The B-200Y and B-200Z tweeters will be unbalanced because they are more efficient than the original B-200X.

Biggles, I, and others have elsewhere discussed this. I've suggested people add a potentiometer or rheostat to control the amount of bypass (signal goes through the bypass instead of the tweeter) because you'll want far less at lower volume levels but without it they can sound too bright at louder volumes. The reduction can make your speakers sound lifeless for low-level listening.

 

[Retrovert]

Bummer I thought I had all the right parts. I just looked at the crimps and its aluminum wire as Retrovert stated. Now what?

Sound like they need to go and I'm not even sure what values they are or details I need to consider on a upgrade.

Copper inductors are inexpensive and the existing ones may be easily replaced. The ordinary 16 gauge versions sold by Part Express or similar supplier should be fine.

 

[Retrovert]

All of the proposed upgrades—inductors and capacitors—are not very expensive (should be under $50) and will make these into speakers you will enjoy owning at a price that is one tenth of the cost of fancy modern speakers that aren't as good.

Think of this as you would any rebuilding of vintage gear. No serious issue exists for you, and you're most of the way you need to go. The drivers and cabinets are usually the big issues, and as you need not do anything on those you're ahead of the curve for most new Bozak owners.

 

[RonaldP]

Wow, and congratulations. To answer your first question, yes you got a great pair of speakers. Not only great looking, but the drivers will backup the looks with great performance. That ceramic B199 woofer will give you some really good slam with enough detail to really impress. The midrange is so full and lush, a wonderful experience.

I see Retrovert stepped up to the plate! You're going to want to build the Bozak N10102 3-way crossovers to Pat Tobin's design. You don't have to do this today, or tomorrow, but this is a necessary addition.

Congratulations!

Biggles

Thanks for the advise. Sound like I should just fix what I have and work on a new ground up build Bozak N10102 3-way crossovers to Pat Tobin's design in the near future.

 

[Retrovert]

Thanks for the advise. Sound like I should just fix what I have and work on a new ground up build Bozak N10102 3-way crossovers to Pat Tobin's design in the near future.

Either way is simple, but since you have a board all you need do is add the inductors and the capacitors instead of building something from scratch.

Shouldn't take you more than a few hours to get them running.

Be careful to remove all of the flux when you do the soldering, as some have used a slightly conductive flux which made debugging the crossover a difficult process. Either water or alcohol, depending up on the flux type.

 

[cubdog]

Those cabinets are beautiful! Congratulations you have some nice speakers.