Bozak Speaker 401a Revival: What To Do?

[John_Doe1987]

I've got a few questions about how to proceed on a restoration/rebuild/improvement of a pair of Bozaks speakers I have acquired. Any advice is appreciated!

1. What to do about the mid-range?
The current drivers I have are the B-199a woofers and the B-200-Y (I think) tweeters. The mid-range was retained by the original owner who used the OEM cabinet as a trunk to carry his things home from college (go figure). My question is: how should I proceed with the mid-range? Should I purchase a set of the B-209 (b) midranges? Or should I go with a different model?

2. Housing the Midranges
The current cabinet is custom made to house solely the tweeters and woofer. Therefore, space is a issue if I end up going with a mid-range unit and housing the three driver system in one cabinet. For that reason, should I build a separate (and external) enclosure for the mid-range, or build a new enclosure to house all of the components?

4. The Crossover
I have read many a threads of the modification and improvements made upon the Bozak system by Pat Tobin. I presumably have the stock Rhapsody xo, which I have been lead to believe is crap. Either way I will need to re-cap the system, so how should I go about that? Should I buy the N10102 xo and go from there and modify it to the modern specifications, or build the new xo from scratch? Is there anything to save from my current one (Inductors)? I'm planning on carrying out the Tobin 104-T modification of the xo, but is that the correct course of action?

5. External Crossover
I have seen many recommending the use of a external xo for the Bozaks. How would that fit in here? Should I use a L-pad? Should I reverse the polarity of mid-range?

As always, thanks in advance for the insight and guidance. I am by no means a expert and am eager to learning more.

 

[twiiii]

Join the Bozak owners club on face book and all of your questions have already been answered. Pay special attentions to Ken's posts. He is always right on with his answers. Just tell him TWI stands behind everything he has written.

I have owed or sold or installed every type of Bozak made from the early 60's until NEAR bought the company in the early early 80's or very late 70's. Right now I have two B-313's which is what you want to have when you are done, three B-4005 low Boy Symphomy speakers and two B-410 Concert Grands. All with B-200Y, B-209 Bc or B midranges, and B-199 A or B-199 Ac woofers. The grands and one symphony have added celestion super tweeters, which I prefer over the B-200 Z tweeter and the Tobin mods.

Sorry the wide angle lens on my iPhone screws up proportions. The center symphony is the same width as the Grands and is is a bit more than half as high and the same depth.

 

[John_Doe1987]

Join the Bozak owners club on face book and all of your questions have already been answered. Pay special attentions to Ken's posts. He is always right on with his answers. Just tell him TWI stands behind everything he has written.

I have owed or sold or installed every type of Bozak made from the early 60's until NEAR bought the company in the early early 80's or very late 70's. Right now I have two B-313's which is what you want to have when you are done, three B-4005 low Boy Symphomy speakers and two B-410 Concert Grands. All with B-200Y, B-209 Bc or B midranges, and B-199 A orView attachment 3464620 B-199 Ac woofers. The grands and one symphony have added celestion super tweeters, which I prefer over the B-200 Z tweeter and the Tobin mods.

Sorry the wide angle lens on my iPhone screws up proportions. The center symphony is the same width as the Grands and is is a bit more than half as high and the same depth.

Thanks for the info, you certainly seem spot on with the advice. I have applied to the group.

I'm just concerned about the uniqueness of my situation. I have no mid-range, and the cabinet housing the woofer and tweeter do not have the space to accommodate a mid-range unit. So, I'm presented with two options: build a separate enclosure for the mid-range (external to the unit) or buy/build a housing to encapsulate the three drivers in one.

Do you have any advice on that front? I trust the group has plentiful information of the crossovers.

 

[Dswankey]

@John_Doe1987

@twiiii KNOWS his stuff, I tried to help the best I could utilizing Google Search and I think I got close however if he suggests joining that FB group then I would heed that.

One last thing we love Pics here and I'm assuming on that FB forum they do to so be sure to share some pics over there it helps

 

[twiiii]

A close friend of mine and the club is now deceased and was the clubs librarian. She kept track of literature, drawings, photos and upgrades. She had a set of Grands, Symphony Speakers and 4 custom 302's. The were the best I ever heard, pushed with a Sansu 9000 Quad integrated receiver. The custom 302 cabinets were about the same height as her Modern 4000's. But only 18" wide and about 18"deep. As I remember I think the interior volume was just over 7 cu ft. The tweeters were at the top of the cabinet with the midrange just underneath the tweeter pair. The woofer was as near to the floor as possible. There was enough room to add a second woofer on top of the first, but I don't think she ever did. She changed the woofer crossover to 400 HZ, and added tobin mods. It was Ok, but I demonstrated to her that high snare, cymbal, brush sounds were still missing from the 302's for which she had the custom cabinets made. She bi-amped her Grands and modern Symphony speakers using direct couple MC 7200's for the woofers and CM Labs mono direct coupled amps for the mids and tweeters. Using a N-107's between the tweeter and mids with the Tobin mods. As I remember she was using a Bozak Disco mixer as a pre-amp for the Grands and Symphony speakers. We all miss her. She had great hearing and having been a percussionist at one time loved Jazz, Country, and some classical music. She also loved choirs and small vocal groups. That she said that was why she owned Bozaks because they produced the human voice so well.

 

[rmeade]

Greetings Mr. Doe!

I have two different sets of the Bozak 302a. I have followed Bozak discussions here for a number of years (to update my speakers) but I am not a member of the facebook group. Here are a couple of thoughts, collected from AK.

- Cabinet size: Apparently the Bozak woofer is very sensitive to the size of the cabinet. You mentioned that your custom cabinets are too small for inclusion of the midrange. Measure its size and then consider the recommendations, which I think is a 5 cubic foot cabinet (someone please correct me if I am wrong). The 401a seems to be in a 3.45 cubic foot cabinet. The 302a Urban (for example) is a 6.6 cubic foot cabinet. If your custom cabinet is smaller than the 401a, it might be a real constraint on woofer performance.

- Acoustic stuffing of the cabinet. Most recently I read a thread here on the benefits of the original cabinet stuffing. This includes the side walls and a curtain. This may now be absent on your custom cabinets. The curtain is very important for woofer performance.

- Tobin mod: There are a number of advocates here on the Tobin modification. A couple of years ago a number of threads surfaced on the complexity of its implementation and the variation in the resultant performance. Then a recent thread included discussion about using the original design for the crossovers and not Tobin Mod. There are many compromises made in the design of crossovers. It is not simple to re-engineer existing designs and obtain improved results.

- Midrange: The Bozak midrange is well regarded.

http://www.cyberbilly.com/chicken/Bozak/1970%20Bozak.pdf

401a: https://www.radiomuseum.org/r/bozak_rhapsody_b_401.html


So, it might be best to try to recreate the original design.

 

[John_Doe1987]

@twiiii @rmeade thank you for the insight! I will measure the dimensions of the cabinet, but I know already that no curtain exist in them. More to the list of repairs I suppose!

 

[John_Doe1987]

So after some digging (or should I say unscrewing) in the speakers I have found the following:

1) There is no crossover. Only two caps lie between the tweeter and woofer. To proceed with the restoration should I source a N-102 and then re cap it? Or should I simply start from scratch?

2) The dimensions are 19.5x18x25.75 (externally) and 18x16x24 (internally). So, according to rmeade's specifications the cabinet is indeed fitting for the woofer. That said, what to do with a mid-range unit? What considerations should I take in designing a enclosure for those?

I was able to gain access to the Bozak group, so I will bring to look through the archives there. A brief parse has not answered either of the above questions though, but I did find much information on the tobin modifications which is very helpful!

 

[Steve Smiley]

Your cabinet is a little small for the woofer, but it will do. You want to enclose the mid with a flower pot/bowl so that the woofer doesn’t affect it. That’s why I say your cabinet is a little small. The flower pot takes up a lot of space. And the Bozak woofer loves all the room you can give it. Want to build a new cabinet?

Yes, buy some B209b mid. And then, if you can find a Bozak crossover to recap, that would be an easy route, but building from scratch is a great way to go. And you will need a curtain and you want to line the cabinet with the same material. That material would be cotton batting. Like that used for making furniture.

None of this work is hard, but does take a lot of effort to do it right. And you will absolutely be rewarded for your effort. Plenty of info on AK and the Facebook group. Do the legwork and you will be happy you did. And you’ll learn a bunch along the way.

 

[John_Doe1987]

@Steve Smiley Welcome to the thread! I have seen literature (particularly on the AK forum) praising the benefits of the "flower pot mod".

My question, and forgive me if I have not been clear in wording, is if I should build a separate enclosure, external to the enclosure that houses the tweeter and woofer, for the mid-range (and super-tweeters if they are worthwhile) as opposed to making a whole new enclosure to fit all of the drivers.

I've read some writings online about enclosure construction, and couldn't find any conclusive information on the boons or woes of having the mid-range enclosed separately - all I've read is that it will sound "different" (and we all know how vague that is!)

I agree that the current enclosure is too small to add a mid-range, and I believe the first sensible step in tackling the project is to figure out where to put the damn thing!

Anyhow, thanks for the encouraging words and wisdom!

 

[Steve Smiley]

@Steve Smiley Welcome to the thread! I have seen literature (particularly on the AK forum) praising the benefits of the "flower pot mod".

My question, and forgive me if I have not been clear in wording, is if I should build a separate enclosure, external to the enclosure that houses the tweeter and woofer, for the mid-range (and super-tweeters if they are worthwhile) as opposed to making a whole new enclosure to fit all of the drivers.

I've read some writings online about enclosure construction, and couldn't find any conclusive information on the boons or woes of having the mid-range enclosed separately - all I've read is that it will sound "different" (and we all know how vague that is!)

I agree that the current enclosure is too small to add a mid-range, and I believe the first sensible step in tackling the project is to figure out where to put the damn thing!

Anyhow, thanks for the encouraging words and wisdom!

Oh, now I see what you are getting at.

I say, heck yeah, you could use a separate enclosure. And might I suggest you put the mid, tweets, and super tweets in the separate enclosure with only the woofer in the original cabinet?! That way you get the more directional drivers nice and close together for better convergence and may be able to do away with adding the flower pot on the lids (depending on box size).

I love the idea.

 

[John_Doe1987]

Fantastic!

I've been able to track down the T-S parameters for the drivers, so I should be alright with figuring out the specs of the cabinet.

One issue I noticed when I opened the enclosures back up again was that the B-199a woofers are 16 ohm impedance, not the normal 8 ohm impedance. How do those then work with the B-200Y tweeters? Correct me if I am wrong, but I thought they (200Y) were 4 ohm each (and the pair then being 8 ohm when wired in series). Is the difference in impedance a problem? Should I look for 16 ohm or 8 ohm spec-ed midranges?

Thanks for the help!

 

[Steve Smiley]

The B200y are actually 16 ohm per. The 16 ohm B 209 is pretty available and much less expensive, generally, than the 8 ohm version. You could post in the Bozak Facebook group that you are looking and I bet you would do well there. Then just run it with one tweeter a side for the simplest approach.

For a crossover, you could follow the B-305 x-over diagram, or build the basic Tobin adjusted for 16 ohm. That would take some math but certainly doable.