New to me pair Bozak B-300 now B-302 Urban with issue

[kcline]

I am the 2nd owner of these, they came from an estate in Burlington NC. Issue is one speaker is wired the opposite of the other, since it is a possible user error I very carefully checked all speaker and amp a Fisher KX-200 connections all were correct, today I made a new shorter set of speaker cables and very carefully wired up again, speakers still out of phase, so I changed connection on one speaker and bingo stereo is back and correct and the Bozaks sound very nice. Speaker backs look like they have never been off is it possible original owner played them this way? who knows no one alive had heard these speakers play, they had always been in the den where dads system was, I never saw the electronics for these they were taken by family member. I will one day take backs off and see what is going on for now I will leave alone.

 

[rider33]

those we likely made in the late 50's-early 60's (if label has 'code' on back, first two numbers are the year, third the month of manufacture) which is prime time for Rudy. Also, they sold for about $175 a piece which puts them up near $1,500 cost adjusted. Given that, I sort of doubt they left the factory reversed. A number of them were sold in kit form so the owner assembly might have been wrong also, the backs should come off rather easily once the screws are removed so someone might have been in them as well. They likely sound pretty good now, replace the capacitors (like for like) and you might be surprise how good they can sound.

 

[Retrovert]

The B-300 is a two-way with serious sonic issues. The woofer runs to 1,250 Hz and is somewhat mechanically limited above that, the tweeters use a capacitor to pick up from there. It is the worst-sounding coaxial one is likely to ever hear. (I say this as one of the resident Bozak fanboys, too.)

This thread contains all the gory details on converting the two-way B-300 to the three-way B-302:

https://audiokarma.org/forums/index.php?threads/bozak-b-300-urbans-to-302s.871123/​

 

[rider33]

...It is the worst-sounding coaxial one is likely to ever hear...

my friend I believe there is a wide, wide world of truly horrendous coaxials you have yet to experience
'Not Rudy's finest effort then again it was one of his least expensive. It also had that path-to-improvement
thing which made sense when people often built vs just bought speakers. Add a midrange and you might
be surprised...

 

[Leben]

I have a pair of B-300s that I eventually made into a 3-way with the Tobin mods. Honestly, I was very satisfied with them as 2-ways and could have easily left them that way. There are a lot of nice older speakers that ran the woofer full range and used a simple cap to the tweeter. That combination works well, IMO. Mine as 2-ways sounded wonderfully natural at low to mid volumes. There is plenty of information out there if you want to upgrade but if you’re happy with the sound, there’s nothing wrong with enjoying them as they are. Just my opinion from my experience.

Those are in really nice shape and look great, enjoy!

 

[wiredbecker]

Story goes is that one of my dad's Bozak Concert Grands shipped with reverse polarity from the factory. His best friend noticed the error and modified the crossover to match the other speaker. He's been running them that way since 1967! Someday I'll get in there to check their work and see how these beasts actually measure.

 

[Retrovert]

'Not Rudy's finest effort then again it was one of his least expensive.

The point was to create a low-cost solution and sonic quality was unimportant.

Bozak reduced the end-user price for a single B-300 by $100 per speaker compared to the B-302, which was about $1,500 in buying power in the mid-1960s.

'It also had that path-to-improvement thing which made sense when people often built vs just bought speakers. Add a midrange and you might be surprised...

Midrange and a full three-way crossover (low-pass, band-pass, and high-pass). Just not throwing in a midrange. Which is why the B-300 was the entry path.

my friend I believe there is a wide, wide world of truly horrendous coaxials you have yet to experience

Yeah, fine, whatever, but I don't know any Bozak owner who didn't find the addition of an aluminum-cone B-209 midrange to two-way be the sonic equivalent of Zeus himself descending from Mt. Olympus to personally hand over amazing sound.

 

[nolasally]

^^^ Your opinion, which is not necessarily fact, regarding speaker sonics. Id still take a lowly B-300 over a tempo any day.....

 

[Retrovert]

^^^ Your opinion, which is not necessarily fact, regarding speaker sonics. Id still take a lowly B-300 over a tempo any day.....

Yeah, ok, but I was addressing the conversion of a B-300 into a B302, a conversion for which that cabinet was designed.

The Tempo has a B-450 midrange which is not in the same class as the B-209, and the ported cabinet is too small for the B-199, is ported (i.e. not infinite baffle), is not lined with cotton batting, and has no curtain. Rudy's son-in-law created that to add a smaller speaker to the lineup to better compete with other bookshelf speakers.

 

[rider33]

I think the perception of sound is influenced more by those squishy human bits than most of us let on. There are of course the typical factors like associated components, the room, etc. Then you get into things like the temperature, the humidity, even the time of day to say nothing of the age (and accumulated mileage) of the listener. I've heard known systems of very high quality that sound horrendous at times & I've heard some very simple systems that seem to capture the soul of things. There was this piece in Stereophile years ago, an interview with Dave Brubeck, where he was asked essentially why didn't he pay more attention to playback equipment. He basically said he listens thru, not to the equipment. In a way I think we all do that, what we bring to it influences perception, perhaps as much as the equipment itself. Basically, one man's ceiling is another man's floor but we're all in the same house.

 

[quiet]

My B301 Tempo code 7206 are acoustic suspension, with thick cotton batting on top, bottom, sides and back. It sports a smooth, sweet mid and top end. The adequate bass has less weight but better definition than my 302a Century. No, it doesn't have the unique sound of the 302a. It sounds like a very good speaker of bookshelf acoustic suspension design, and some people may prefer it.
Rudy made speakers to suit his taste. When time came to suit a changing market Bozak hit a home run with the B301 Tempo. I think it's subjectively as good as any competing mid size box speaker of the day. I have many of the usual suspects, KLH 5, Advent OLA, AR3a, Dynaco A40XL…....... And all of those are better than my Utah MK20-A, Realistic Optimus 5b, Fisher XP7b, Criterion 5xb...…......
My preference for the Tempo over Century is in a 14x16x8 room, with 30 to 80 watts.

 

[Retrovert]

My B301 Tempo code 7206 are acoustic suspension, with thick cotton batting on top, bottom, sides and back. It sports a smooth, sweet mid and top end.

A correction: Bozak never made acoustic suspension speakers, it made infinite baffle speakers. From what I previously wrote on the subject.

This is somewhat simplified because I'm trying to hit the essence.

Sealed-Cabinet Types

Infinite baffle is a sealed box which does not use as a restoring force the air compressed by the woofer's backwards movement (backwave). The backwave, instead, is intentionally dissipated and lost inside the cabinet by expanding around baffles and into batting such that it cannot put pressure on the woofer. The suspension on the woofer, of the normal type, instead serves as the restoring spring. So while an infinite baffle cabinet is sealed (nearly but not completely sealed, though, as we'll later see), is is not acoustic suspension. The infinite baffle cabinet is normally significantly larger than an acoustic suspension or ported (bass reflex, transmission line, aperiodic vent or ARU, etc.) cabinet. Bozaks are the most familiar infinite baffle cabinet, but Electro-Voice also made them. Think big box.

Acoustic suspension: is a sealed box which uses as a restoring force the air compressed by the woofer's backwave. The rearward wave compresses air inside cabinet and this forces the woofer to its resting position. The driver's surround must be very soft and floppy so that it does not resist this restoring pressure and moves faster than it would otherwise do. Acoustic stuffing does not dissipate the backwave; it, instead, serves as an acoustic brake to slow the propagation of the waveform, allowing greater excursion and slowing the frontward movement, but it does not reduce the interior cabinet pressure. So while an acoustic suspension cabinet is sealed exactly like an infinite baffle, it is not functioning in the same way because in acoustic suspension the backwave is required for proper functioning.

My B301 Tempo code 7206 are acoustic suspension, with thick cotton batting on top, bottom, sides and back. It sports a smooth, sweet mid and top end. The adequate bass has less weight but better definition than my 302a Century. No, it doesn't have the unique sound of the 302a. It sounds like a very good speaker of bookshelf acoustic suspension design, and some people may prefer it.
Rudy made speakers to suit his taste..

The difference in sound results from the fundamental differences between ported cabinets and infinite baffle cabinets.

The B-301 Tempo uses a ported cabinet, a concept Rudy Bozak felt was inferior because or poor transient and impulse response, and the boomy bass. (I refer you to Bob Bett's writings on the subject.) The pair I had was from the mid 1970s, I think that pair was from 1974 but it's been a while, with a cabinet of vinyl over MDF, fiberglass lining instead of cotton batting, and no curtain present. I no longer have these or I'd post a photo. Ported speakers are less accurate at the low end because the backwave is delayed in time and then recombined with the front wave, and the group delay results in some distortion. This is just how ported speakers work.

I also have a pair of the B-201 Sonora which is a B-800 in a ported cabinet, very similar to the DMS-2500. AK has a thread about rebuilding those speakers to use cotton batting for the lining and no port. See https://audiokarma.org/forums/index.php?threads/bozak-dms-2500-specs-opinions.853824/ . All of the smaller Bozaks were moving to ported designs because it was the only way to compete with other ported speakers, in terms of size and cost. The previous B-800 cabinet was the B-801 in the same cabinet as the three-way B-502 cabinet (like a B-313), and that was an infinite baffle speaker, slightly smaller size than the B-313, which I also own. Off the top of my head the B-801 was four to six times the size of the ported version.

The Bozak company made speakers which could be sold in the marketplace — that's how capitalism works — which is why the designs had to be cheapened (ported) over time so as to remain competitive with low-cost offerings. Rudy Bozak reportedly never liked the B-450 midrange, a lower-cost unit than the B-209, which is vastly inferior to the B-209 he designed. By the time these low-cost bookshelf units were being sold Rudy Bozak was largely excluded from the design process and was out of day-to-day company management. He sold the company in 1977 and died shortly after that in 1982.

 

[quiet]

Yes of course. But my B301 Tempo are as sealed as any speaker I got. And I suggest that it's big woofer and small cabinet size and 3 inch thick cotton batting lining is contributing to the super clean tight bass that my 302a does not have. Very good attack, decay and pitch definition. Just a touch more bass weight would be nice. Nothing boomy about the B301 bass. It's a clean sounding speaker all the way around. It does have the expected reduction in sensitivity, which is not a problem because when it came out there was solid state power to spare.
And that fine little mid ain't as sensitive either, but it matches the rest of the speaker output and sounds smooth as silk.
True an infinite baffle speaker it is, but it's acting like a very good acoustic suspension.
Bozak made the best of the wrong woofer in the wrong box. What luck I say.
And it missed out on the popular vinyl wrap thing. I don't see anything cheap about the speaker. Same good build as the 302a Century. Nice busy crossover too.
No, Rudy didn't like the speaker. He didn't like little speakers period.
I'm not a ported or vented fan, but darned if my big ported Rectilinear 111 don't sound like the bees knees.
Bozak did make some ported speakers, but this ain't it.

 

[Retrovert]

Yes of course. But my B301 Tempo are as sealed as any speaker I got. ... True an infinite baffle speaker it is, but it's acting like a very good acoustic suspension.

It cannot be, and is not, an acoustic suspension cabinet. That is impossible.

I've clearly explained the difference in the surround and how acoustic suspension works. It is still an infinite baffle, just in too small a box.

Not all sealed boxes are acoustic suspension.

Bozak did make some ported speakers, but this ain't it.

The Bozak B-301CD Tempo, which I formerly owned, is, indeed, a ported speaker. I cannot speak to other versions. Notice the port in this video.

Once again, we see how trying to pin down Bozak model numbers to a consistent configuration is like trying to hold sand.

My guess is that Bozak was trying to reduce costs and deepen the bass, so it stripped out the cotton batting and added a port. The crossover had a brightness control as well, likely to compensate for the boomy bass.

 

[quiet]

All the B301 Tempo were sealed. It was designed on Rudy's watch, 1965 I think. The ports followed later with the suffix versions. To bad. Because the B301 is a very good speaker. It just failed to have the nasty mid base bump that was required later in the game.
I think the reduced box volume and increased batting thickness (3 inches all around takes up a lot of room in a 12 inch wide box) does provide some of the woofer control. When I push the woofer in and let it go it springs right back. If I hold it in for 10 seconds it takes almost 2 seconds to return. My 302a doesn't do that. And I don't think the box is to small for it's intended use. Yes it sounds different than the 5 ft box. No it's not an organ speaker. Yes it's ability to play voices and acoustic instruments is outstanding. I say this while having it and the 302a that I like after recap and will not alter in the room.
The first cross point is to high. I think. On maybe that little mid won't go down to 800.
The 302a came to me first, then the B301. I wasn't expecting much from the little B301. I was wrong. This is the best little sealed box speaker I got. It took a while to realize that.

 

[kcline]

I hope next week to the backs off and see what is inside. I will see if I can tell which speaker is wired up backwards.

 

[Retrovert]

All the B301 Tempo were sealed. It was designed on Rudy's watch, 1965 I think. The ports followed later with the suffix versions. To bad. Because the B301 is a very good speaker. It just failed to have the nasty mid base bump that was required later in the game.

I am quite familiar with the early bookshelf Bozaks as I own several pairs and have owned more. The B-502 Spinet (which I own in rough condition) is an earlier draft of the B-313 placed the slightly smaller Sonata No. 1 cabinet, as is the B-313 (which I also own). I also have the B-201 Sonora which is similar to the DMS-2500. Again, a small ported cabinet which is unsuitable for the infinite baffle driver.

I think the reduced box volume and increased batting thickness (3 inches all around takes up a lot of room in a 12 inch wide box) does provide some of the woofer control. When I push the woofer in and let it go it springs right back. If I hold it in for 10 seconds it takes almost 2 seconds to return. My 302a doesn't do that. And I don't think the box is to small for it's intended use. Yes it sounds different than the 5 ft box. No it's not an organ speaker. Yes it's ability to play voices and acoustic instruments is outstanding. I say this while having it and the 302a that I like after recap and will not alter in the room.

I am not making deprecating comments about Bozaks and don't need convincing. I am, after all, one of the resident Bozak fanboys and have piles of spare drivers in storage, just in case the Zombie Apocalypse hits and makes them hard to find.

What I am clearly stating is that the design guides from Bozak itself suggest 5 cu. ft. as the minimum box size for the B-199 woofer. As the cabinet size shrinks, so does the lowest bass response correspondingly climb. That's just fact.

This is why the B-313 (again, which I own) with its 2 cu. ft. of volume is incapable of duplicating the bass of the B-302. Cramming the B-199 into so small a box causes pieces of the bass response to break off. But I simply do not have the space for a B-302 to converge in my apartment living room, nor do I have the depth for the sound to properly converge. I must, therefore, use a smaller cabinet and endure the reduction in bass. Which, in all truthfulness, isn't a problem as I live in an apartment and I don't resonate my neighbors.

The first cross point is to high. I think. On maybe that little mid won't go down to 800.

A 4.5 inch driver is unsuitable for significant response at 800 Hz, let alone the 400 Hz the Tobin mod uses to improve low-end linearity and remove the crossover hit from an audible portion of the midrange.

The 302a came to me first, then the B301. I wasn't expecting much from the little B301. I was wrong. This is the best little sealed box speaker I got. It took a while to realize that.

I have my dad's pair of low-numbered AR-3 which he bought new. The sound quality is impressive for the size, and I have to say it clearly beats my B-313 for low-end response, but the AR's midrange is not as clear as the B-209. I also have the AR-2ax which is not as good as either.

I stand behind my comment about the B-450 midrange stands: it is inferior to the B-209, Rudy Bozak never liked it, and it was introduced as a cost-savings measure. I would have replaced it in my B-301CD, but that had so many other defects (porting, fiberglass, lack of crossover, vinyl covering, etc.) that the work would have been pointless.

 

[quiet]

.
I assumed the 4.5 driver was used because it matched better with the 199 in the little box. Since the 199 wasn't going down to the basement anyway, no need for the 800 extension. Just let the 199 go on up. And it works well enough.
I don't fault the little sealed Bozak box for it's limitations. It sounds very good given bookshelf market design constraints. At this point I'm glad Rudy didn't design a new or smaller woofer for the speaker, even if it had provided better bass extension. Because of how clean the bass is. Yes, it is a little constrained though.
Voices are the best. That's why I keep going back to the B301.
I don't know if the A301 would perform in a larger room or not. I can tell my 14x16 room isn't big enough for my 302a. But I still like it, and won't give it up. It's the best speaker I have for organ music. I didn't listen to organ before the 302a showed up. Now I can.
Maybe I like the B301 so much because it's speed allows it to adapt to music changes over the years. To bad I won't ever hear it with the B209 driver, and crossed lower.
Have you had the opportunity to try any of the little sealed 199 Bozak's?
I've heard only 302a and B301 Bozak's.

 

[Retrovert]

I assumed the 4.5 driver was used because it matched better with the 199 in the little box. Since the 199 wasn't going down to the basement anyway, no need for the 800 extension. Just let the 199 go on up. And it works well enough.

That view is contrary to the A/B comparisons done by those implementing the Tobin modification. The B-199 does better stopping at 400 Hz than 800 Hz.

The B-450 is an inexpensive driver, being smaller and less sophisticated. It has no advantage over the B-209 and cannot compete except on price. I have never heard anyone wax rhapsodic about its properties.

Have you had the opportunity to try any of the little sealed 199 Bozak's? I've heard only 302a and B301 Bozak's.

I have written about my ownership of the bookshelf Bozaks and my opinions of same.

 

[quiet]

What's the result of the Tobin mod on the B301?
Is the performance of the sealed B301 any better or worse than the small ported Bozaks?