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Bozak 302 Mid Century Speakers

richartistic

richartistic

Active Member
I found a nice pair of Bozaks locally today. I'm pretty sure they are the 302 Models. They have grill cloth all the way around. Top, sides and bottoms are all plywood with the top and the bottom veneered in Birch or Maple. Pretty decent condition overall. These are solid and fairly heavy.
These have a very deep bass response. I'm thinking they sound better than good. Very clear as well on the instruments and vocals.
Although the cabinets aren't bad looking, I'm partial to a bit fancier cabinets. I plan to build new ones, Solid African Mahogany tops with veneered bottoms as well as more visible base supports. I want these to be a focal point since I'll be keeping them. My thoughts are to keep the size about the same but curve the front of the top and bottom for a nice effect.
Should be a fun project. 001.JPG 002.JPG
 
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How do you like yours? I'm pretty jazzed about the sound. Looking forward to making new cabinets, but so far so good. I got them for a fairly low price $120 for the pair. Pretty weighty cabinets as well.
 
I believe after doing some very basic research that these might be the Bozak B302A Models since they have the midrange. The more I listen, the more I like the sound. If anyone has an idea as to what decade these were produced, I'd love to know. My guess is sometime in the 1960s, but that's simply a guess.
 
I have 2 pairs of 302 variants. One is identical to that pictured and one is a bigger, custom, cabinet. Both sound great and actually greater than almost all the other speakers that I have (perhaps 25 different pairs). With Bozak the bigger cabinet sounds better than the smaller cabinet. There are also suggested mods to the crossover, here on AK and the applicability of the mod depends on the type of tweeter that you have. So, understand your components before you consider changes.
 
GeeDeeEmm,
Those are Sony SS9500 Bongo Speakers, Vintage 1972. They are very rare speakers as they were only made for one year I'm told. I've had them about a year or so. Found them locally., They made 2 sizes, the smaller ones being SS9300. They are mullti-directional, 6 speakers and they don't sound bad, but as far as being really full, they are not, but they make good background and are good for Classical. They just are so unusual, Walnut veneer and they are made to be used as end tables, but they came originally with 2 vinyl cushions on top so that they could be used as seats in bars and such. The cushions had 2 colors in each cushion. One side was Red and the other black so one could turn them over depending upon the decor. Luckily mine aren't peeling whatsoever, the walnut is all there. They need to be resprayed with lacquer but are really in pretty nice shape, considering they are 45 years old. I'll probably do that sometime here before the end of the year.

I get more comments on those speakers than any others. Great conversation pieces.
 
Thanks Meade, I've heard about the Mods but I just got them yesterday so not interested yet. I do like the sound as they are. I've heard good and bad reports on those Tobin mods on other speakers and some say they weren't happy with the sound. I guess it is all in the ear of the beholder. I'll have to learn some about that.

When I get the new cabinets going, I'll post photos.
 
Hey man,

Bozaks are generally not a plug and play vintage loudspeaker system. You can certainly just replace the capacitors and go on your merry way, at the very very least. But there are recommended changes and upgrades that have been proven to greatly increase their performance. Unlike many other manufacturer's products, it is accepted and applauded to do these modifications. Not only that, you will be cheered and patted on the back for making your own cabinets along with all the modifications. I would suggest you join the Bozak group on Facebook as well.

You have the 1950's design Bozak B302a's. I'd be willing to be you have the B200X tweeters (paper cone with chrome dust caps, the original B209 paper cone mid, and the early B199 woofer (doesn't have the power handling of the later versions). You can remove the back and take a look of the back of the midrange. There should be a 3 or 4 digit date code stamped on the back. It's very easy to decipher. This will give you a general idea as to when they were assembled.

I love that design, and covet those Bozak script logos. They're my very favorite.

Since you've already mentioned that you're willing to build new cabinets, I would suggest you leave these alone. Just replace the caps. Build your new cabinets with a minimum of 5 cubic feet. I would suggest going with 6 cubic feet to make room for the drivers, and whatnot. Then source a later Alnico or Ceramic pair of B199's, B209b or B209c mids (alnico or ceramic aluminum cones), the later aluminum cone B200Y tweeters and a pair of the Bozak 3-way N10102 crossovers. These crossovers you will do Pat Tobin's 104T changes. Please keep in mind, Pat Tobin's changes are all within Rudy Bozak's original design. You're not doing anything Rudy didn't already build into, or approve of. Instead of using Pat's 7.5ohm resistor in the tweeter's leg of the crossover, install an 8ohm 15 watt l-pad to attenuate the tweeters to your liking. From the factory they were mounted over the woofer, that's too low. The original crossover schematic and Pat Tobin does it as well, attenuates the tweeter by 9db. That's too much for the B302's.

The later drivers are far superior for performance vs the original 1950's drivers. It's worth the time, money and effort to source later drivers.

Biggles
 
drbiggles said:
Hey man,

Bozaks are generally not a plug and play vintage loudspeaker system. You can certainly just replace the capacitors and go on your merry way, at the very very least. But there are recommended changes and upgrades that have been proven to greatly increase their performance. Unlike many other manufacturer's products, it is accepted and applauded to do these modifications. Not only that, you will be cheered and patted on the back for making your own cabinets along with all the modifications. I would suggest you join the Bozak group on Facebook as well.

You have the 1950's design Bozak B302a's. I'd be willing to be you have the B200X tweeters (paper cone with chrome dust caps, the original B209 paper cone mid, and the early B199 woofer (doesn't have the power handling of the later versions). You can remove the back and take a look of the back of the midrange. There should be a 3 or 4 digit date code stamped on the back. It's very easy to decipher. This will give you a general idea as to when they were assembled.

I love that design, and covet those Bozak script logos. They're my very favorite.

Since you've already mentioned that you're willing to build new cabinets, I would suggest you leave these alone. Just replace the caps. Build your new cabinets with a minimum of 5 cubic feet. I would suggest going with 6 cubic feet to make room for the drivers, and whatnot. Then source a later Alnico or Ceramic pair of B199's, B209b or B209c mids (alnico or ceramic aluminum cones), the later aluminum cone B200Y tweeters and a pair of the Bozak 3-way N10102 crossovers. These crossovers you will do Pat Tobin's 104T changes. Please keep in mind, Pat Tobin's changes are all within Rudy Bozak's original design. You're not doing anything Rudy didn't already build into, or approve of. Instead of using Pat's 7.5ohm resistor in the tweeter's leg of the crossover, install an 8ohm 15 watt l-pad to attenuate the tweeters to your liking. From the factory they were mounted over the woofer, that's too low. The original crossover schematic and Pat Tobin does it as well, attenuates the tweeter by 9db. That's too much for the B302's.

The later drivers are far superior for performance vs the original 1950's drivers. It's worth the time, money and effort to source later drivers.

Biggles
Click to expand...
Hi,
Thanks for all the information. I haven't any idea what has already been done to these, however my guess is not much. They came from a person whose Brother in Law passed on, from what I gathered when I purchased them yesterday. I'll definitely be building new cabinets for them as the ones they are in are simply a rectangular box. Not much styling whatsoever. The new cabinets will be solid African Mahogany tops with a curve in the front.
 
Hey man,

Make sure you pass along those cabinets to someone who will use them. There are many out there, like myself, who love those! If you're in the SF Bay Area, let me know.

Do not build any speaker cabinet from solid wood. You'll have severe resonance issues, not cool. I have a pair of custom 1959 Bozak B302a cabinets that are made from solid wood. Avoid this at all costs. 3/4" plywood, marine ply if you can afford it. The denser the plywood, the better. The fewer voids in the plywood, the better. Then veneer as you please.

The B200x tweeters die before 10k, and their response is spiky. But people have reported to enjoy them. I listen to mainly music from the 50's and the 60's. I find the x tweeters quite dull and hard to listen to with anything that has horns.

The early B209 mids have a paper cone, versus their later versions which are aluminum cones. They don't suck, but they're nothing to write home about either. They too suffer from spiky response.

The early B199 woofer sounds wonderful. That's not a standard paper cone woofer. It's a blend of paper and wool, exceptionally detailed. It just simply can't handle the power of the later ones.

If you do plan on keeping these drivers and moving them over, then plan on installing a cover over the back of the midrange. Bozak did this for later Bozaks. AK member Retrovert came up with a brilliant solution. Use 8" plastic flower pots. With today's computer modeling software, we now know that tubes are no good for isolating the midrange. Line the flower pot both inside and outside with 1" of cotton upholstery batting. It was once believed that crossing the woofer and the mid over at 800Hz wouldn't cause any issues with the backwaves of the woofer messing with the midrange. This is not true. Once the midrange is sealed from the woofer, your midrange will become remarkably more precise. It cleans it up pronto.

The capacitors in your crossover probably started to drift back in the late 1960's. Your crossover points are off, your ESR is probably very high. This results in very poor reproduction in your mids and highs. It kinda sounds like a blanket has been tossed over your cabinet.

Biggles
 
drbiggles said:
Since you've already mentioned that you're willing to build new cabinets, I would suggest you leave these alone. Just replace the caps. Build your new cabinets with a minimum of 5 cubic feet. I would suggest going with 6 cubic feet to make room for the drivers, and whatnot. Then source a later Alnico or Ceramic pair of B199's, B209b or B209c mids (alnico or ceramic aluminum cones), the later aluminum cone B200Y tweeters and a pair of the Bozak 3-way N10102 crossovers. These crossovers you will do Pat Tobin's 104T changes. Please keep in mind, Pat Tobin's changes are all within Rudy Bozak's original design. You're not doing anything Rudy didn't already build into, or approve of. Instead of using Pat's 7.5ohm resistor in the tweeter's leg of the crossover, install an 8ohm 15 watt l-pad to attenuate the tweeters to your liking. From the factory they were mounted over the woofer, that's too low. The original crossover schematic and Pat Tobin does it as well, attenuates the tweeter by 9db. That's too much for the B302's.

The later drivers are far superior for performance vs the original 1950's drivers. It's worth the time, money and effort to source later drivers.
Click to expand...

Normally I agree with everything Dr Biggles suggests regarding Bozaks, but in this case I'm a little confused. Dr B, you seem to be suggesting that he replace most of the drivers in the new enclosures he's going to build. I'm not sure how that makes sense. Why dismantle these at all if you're not going to use the current enclosures, mids, tweeters, or crossovers?

To the OP, if you like the sound of what you've got, and want to build new enclosures, then I'd suggest the following:

1) Build the new enclosures a bit larger, as Dr Biggles suggests.
2) Remove the tweeter array from the woofers, and place them higher up in your new enclosure (keep this in mind as you're laying out the drivers in your new enclosures).
3) Build a subenclosure for the midrange to isolate it from the back pressure from the woofer..
4) Recap as you can. If your existing Bozak crossover allows for changing the bass/mid crossover frequency from 800 to 400, do it.

My .02,

bs
 
drbiggles said:
bshorey,

You didn't read my reply, you donut! I said that I recommend leaving these 1950 cabinets alone. Look up there, first sentence.

xo, Biggles
Click to expand...

Ah, my bad, didn't realize you were suggesting to leave his entire speakers alone and embark on a totally new build, I read it as leaving those cabinets alone..

Sincerely,

Mr Donut ;)
 
bshorey,

Yeah, if they were mine I would strip and reload with later 60's guts. I lurve the primitive 1950's flavors.

Biggles
 
Hi again,

I'm pretty certain that the idea of 'resonance' off of a solid wood piece is an urban legend or myth. The idea that the density of the wood would cause resonance doesn't strike me as very plausible.

"Do not build any speaker cabinet from solid wood. You'll have severe resonance issues, not cool. I have a pair of custom 1959 Bozak B302a cabinets that are made from solid wood. Avoid this at all costs. 3/4" plywood, marine ply if you can afford it. The denser the plywood, the better. The fewer voids in the plywood, the better. Then veneer as you please"

If you think about it logically, the specific gravity of woods is quite different, even among a species like Red Oak. I've been a professional woodworker for about 35 years now, and I can assure you that there is extreme differences in the density of wood across the board itself.

Resonance will only occur when the object impinging on the natural frequency of the other object vibrates at the same frequency of the natural frequency of the object upon.which it is acting. i.e. the driver cone itself would have to act upon the solid wood with the same frequency as the resonant frequency of the solid wood in question.

The idea that any type of plywood available on the market today is denser than natural African mahogany which is what I'll be using, or even hard maple, etc... is stretching things a bit.

The specific gravity of African Mahogany ranges from 495 kg/cu. m to 850 kg/cu. m. That is pretty hard. Mostly it is above 750 Kg/cu. m.

I can assure you that no matter what plywood you are using, marine grade or otherwise, it most likely has a lower specific gravity than does african mahogany

Plywood today is generally made from 4 species of wood, birch, pine, poplar, and spruce. There are hardwood core plywoods and appleply brand which have few voids, however even with a large number of voids in the plies, the percentage overall that amounts to void areas vs. solid areas is miniscule and as such wouldn't affect the specific gravity of the plywood that it is even noticeable.

Now, the specific gravity of most plywoods is less than 700 kg/ cu. m. They range from about 500 to 700.

If you are having problems with resonance in your cabinets, it is most likely a problem with rigidity of the cabinet itself. Bracing is a big factor in cabinet construction. I'd look to the lack of bracing in your cabinet as the culprit.
 
Hey,

There is a very important, the most important point of all, the batting. I don't know what's in your early 302's, but what should be in there, and what must be in your new cabinets, is 1" 100% cotton upholstery batting. Bozaks are an Infinite Baffle design. This means that the internal batting must allow the backwaves of the woofer to dissipate, go away. This fakes out the driver thinking there is no cabinet. Your secret weapon is the hanging curtain inside the cabinet. Without it, the performance of the woofer will be greatly affected, it's nasty. The hanging curtain must be a little heavier weight than the 1" upholstery batting, go with 2". This will give the curtain enough weight to help with the backwaves and just not blow around in there.

I'm going to line my solid wood 302's with 3/4" plywood. If they'd just built them out of something denser to begin with, I wouldn't have to bother. I wish you well in your endeavor.

Biggles
 
bshorey said:
Normally I agree with everything Dr Biggles suggests regarding Bozaks, but in this case I'm a little confused. Dr B, you seem to be suggesting that he replace most of the drivers in the new enclosures he's going to build. I'm not sure how that makes sense. Why dismantle these at all if you're not going to use the current enclosures, mids, tweeters, or crossovers?

To the OP, if you like the sound of what you've got, and want to build new enclosures, then I'd suggest the following:

1) Build the new enclosures a bit larger, as Dr Biggles suggests.
2) Remove the tweeter array from the woofers, and place them higher up in your new enclosure (keep this in mind as you're laying out the drivers in your new enclosures).
3) Build a subenclosure for the midrange to isolate it from the back pressure from the woofer..
4) Recap as you can. If your existing Bozak crossover allows for changing the bass/mid crossover frequency from 800 to 400, do it.

My .02,

bs
Click to expand...
Yes, I'm in agreement with you. I'm not interested in sourcing all new parts for my new cabinets, woofers, tweeters, crossovers, and these "Tobin mods". I plan to build new cabinets that are a bit more stylish and to my liking. I plan to use Solid African Mahogany for the top and then I'll use ply for the sides and bottom, veneering them with African Mahogany. I like the reddish look. I may incorporate some curly maple just as a contrasting wood. Right now it isn't even put down on paper. I'll probably use some parts for the new cabinets, for certain the badges. I like the "Bozac" in script. That looks very neat.

BTW, I had heard about removing the tweeter array from the woofers. I may do that and even place them up on top somehow in a nice small attached cabinet. I have some Utah Speakers that were my father's and I'll make bookshelf speakers to match out of those. It will be a fun project for sure.
 
Dr Biggles,
Thanks for all the information. I'm grateful. I will open these up later this evening and I'll take some photos of what I have. If there were a way to easily send you the empty cabinets I would do so, but I'm in Colorado. I'll let everyone know what I come up with for cabinet design, but I'm looking forward to making nice new pristine cabinets. :jump:

Enjoying hearing all the stories and information. :D
 
richartistic said:
Dr Biggles,
Thanks for all the information. I'm grateful. I will open these up later this evening and I'll take some photos of what I have. If there were a way to easily send you the empty cabinets I would do so, but I'm in Colorado. I'll let everyone know what I come up with for cabinet design, but I'm looking forward to making nice new pristine cabinets. :jump:

Enjoying hearing all the stories and information. :D
Click to expand...
Rich glad you found some Bozaks.
 
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