Yes, another Bozak Symphony rebuild thread

Johncan

Record collector
About 15 years ago, I rescued a pair of Symphony's from a old cabin in the mountains of Georgia. They were built from a kit and have seen better days. The good news is all the drivers work and the bowls are present on the midrange. I found a speaker/cabinet repair company in the Atlanta area that is willing to repair the cabinets and update the caps in the crossover.

Can someone please provide me with the schematic for the Symphony crossover. It looks like my crossover is the 104.

It looks like I have two different versions of the B-199 (one is the B-199A and the others are B-199AC). All are 16 Ohms. Will this made a sonic difference?

The curtain and the insulation in one the cabinets is severely rotting and falling apart. What can I replace that insulation and curtain with?

And lastly, the speakers did not have any grill cloth on the grills. The grills are there, but are naked. Where can I locate acoustical grill cloth? I like the look of the Modern grill cloth.

Thanks in advance.

John

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Your one B199A has an Alnico magnet, the others are ceramic. Looks like most of your drivers have ceramic magnets and were made in 1972/73. You could replace the one woofer with a B199Ac so they're all an exact match, but it's not that big of a deal.
 
Whaaaat, another Symphony rebuild?! Good luck with your restoration. I look forward to keeping up with your progress.
 
Hey John,

It's recommended that you rebuild your crossover to Pat Tobin's 104T schematic. However, I'm not familiar with the inductors you have in your crossover, so I'm uncertain as to how to proceed. Hopefully, someone here will pipe up and enlighten us. Or you can stop by the Facebook Bozak Group and ask there, they will know for sure. They have a Files section and may have the original schematic.

The sonic difference between an alnico B199 and the ceramic B199 is actually audible. I did A/B tests. The alnico is a little warmer, more musical. Will you hear a difference? Maybe, maybe not. The 16ohm B199's are tough to come across and can be on the spendy side when compared to their 8ohm counterparts. You can either buy an alnico and put it in the other cabinet to balance it out. Or, buy a ceramic version to complete the set. Either way does not matter.

As far as the grill cloth goes, internet searches will be your source. Or, traveling locally to fabric stores to see what you can dig up. Since you like the more modern solution, this may be far easier. You may want to search for vintage guitar grill cloth, or something similar. There's some cool stuff in there.

Replacing the cotton batting will be the more difficult project. What you do to one curtain, you will have to duplicate for the other. You must use 100% cotton batting, or wool. Try to match the weight and stiffness of your good original curtain. This is one solution I haven't been able to complete, yet. I suggest 100%, 1" cotton batting for the cabinet. But this will not work for the curtain, it isn't stiff enough. All materials, thickness and stiffness you will be able to hear. It all makes a difference.

Biggles
 
Biggles is correct that the hanging curtain must be a solid piece of cotton batting. I have suggested purchasing thick cotton batting from upholstery supply stores or furniture refinishing services. Offering to pay cash often makes stores more willing to sell supplies.

You might want to wade through this thread as it documents most of the tweaks and modifications:
This includes the flower pot modification which creates an ideal midrange bell to prevent the woofer from modulating the midrange, and vice versa:
 
About 15 years ago, I rescued a pair of Symphony's from a old cabin in the mountains of Georgia. They were built from a kit and have seen better days. The good news is all the drivers work and the bowls are present on the midrange. I found a speaker/cabinet repair company in the Atlanta area that is willing to repair the cabinets and update the caps in the crossover.

I suggest you also replace the inductors.

You have the later Bozak crossovers which use inductors with ferrite cores; these unfortunately suffer from non-linear distortion. Depending upon the year, these may also be aluminum, which has higher DCR. (Just like house wiring.) Adding a core increases the inductance with less wire, and thus lowers the amount of copper required and thus the cost, but the properties make them unsuitable for audio purposes.

Biggles has used the Jantzen inductors and elsewhere documented this. I suggested those as a lower-cost replacement for the original Bozak inductors when he was building crossovers from scratch. You don't need to purchase the ribbon coils, which are more expensive and may not offer any sonic improvements despite the claims.
 
I suggest you also replace the inductors.

I have two N-10102 crossovers that are not in any cabinet enclosure. Would it be better if I had those updated and/or modified?

I will also ask the speaker rebuild company what they may have for the curtains.

Sorry for the delayed response. I was with family and did not access my computer.

Thank you for the all the info and feedback. It is appreciated.

John
 
I have two N-10102 crossovers that are not in any cabinet enclosure. Would it be better if I had those updated and/or modified?

If those are the old style, non-cored, copper inductors, yes, that would be beneficial.

Iron- or ferrite-cored inductors save money but do not sound as linear or as nice.

I will also ask the speaker rebuild company what they may have for the curtains.

A suggestion: instead of asking what is available, or for the tech's "opinion", make a specific request for thick cotton batting. If you're paying for a rebuild, you're in charge of what gets done.

Techs have insisted to Bozak owners that fiberglass stuffing is perfectly fine, when it is not. Most techs have never encountered a Bozak, and do not understand infinite baffle speakers, which leads to misery. Fiberglass must never be used, and traditional stuffing, as in a bass reflex or acoustic suspension, is not suitable. This is what most techs know about.

The lining of cotton batting and the curtain are critical to a Bozak. The curtain exists to permit the backwave to escape on the curtain's sides and then enter the rear chamber where it dissipates without being able to put any pressure on the driver. Think of this as an acoustic muffler. The name "infinite baffle" means that the backwave is never heard and does not affect the driver. This is why the curtain must be sound absorbent and freely swing. It is why UltraTouch—dense without loft, rigid and hard—ruins speakers and why I repeatedly tell people to not use it. Make sure your tech is not using this product as it will not work, as has been amply demonstrated. I suggest reading about Biggles' misery from UltraTouch.

Thicker cotton batting is available from upholstery supply stores and online distributors. It can likely be purchased from any furniture re-upholstering store which can order exactly what you want from a distributor which would not otherwise do business with you on a one-time basis. (I have found that the magic phrase "I will pay in cash and give you a deposit" works wonders on most small businesses.)

Thank you for the all the info and feedback. It is appreciated.

You're welcome.
 
Retrovert and Drbiggles held my hands throughout my CG restoration effort. I ended up finding this option for the cotton batting. Shipping was cheap too and it got to me fast. A Bozak Facebook member in China ordered some too. Local shops just don't carry the stuff any more and if they do it is expensive. If you get it, make sure installing the cotton is only done after all other work is done so you don't keep disturbing it. You can use it for the curtain too I guess, but it doesn't have a lot of structure to it. I got some wool fabric for that application that I am trying out.

https://www.onlinefabricstore.net/cotton-upholstery-batting-fabric-.htm
 
You can use it for the curtain too I guess, but it doesn't have a lot of structure to it. I got some wool fabric for that application that I am trying out.

As has been repeatedly explained in many threads, the hanging curtain in the Bozak infinite baffle must be absorptive, flexible, and free swinging; it must not be hard or reflective. Wool fabric, such as felt, is too dense for this purpose. This is why UltraTouch is totally unsuitable for the curtain or sides; it lacks loft and presents a hard surface. Using wool fabric is like using UltraTouch. Bozak did not use this material for a very good reason.

Experiments have demonstrated that any material other than the soft cotton batting significantly reduces the bass response. The cotton batting is acoustically superior to the other alternatives, including Kimsul, Tufflex, or Cellu-Down which were also used by Bozak, and vastly superior to fiberglass stuffing, including for handling reasons.

Infinite baffle must completely lose the backwave. That requires cotton, as Bozak discovered, having originally used acoustic insulation used by other manufacturers. (Roger Russel selected a fire-retardant treated version of Tufflex while at McIntosh in the 1970s.) An enclosed midrange may have similar issues, if the backwave reflects, but it is a lower-power driver so the issue of a powerful backwave suppressing cone movement is not as significant.

I urge everyone rebuilding a Bozak to carefully research the curtain issue and talk to Bozak owners before choosing alternate, and notably hard, fabrics which do not function the same way and damage the bass response. Until one has heard it done the right way it is difficult to understand what is missing when doing it the wrong way.
 
Ok. Thanks for all the assistance so far. I have more questions.

As mentioned in thread #10, would this stuff work for the curtains?
https://www.onlinefabricstore.net/cotton-upholstery-batting-fabric-.htm

If the other insulation is OK (not rotting or water damaged), can I keep it in the cabinet and not replace it?

One of the backs of the Symphony cabinets got water damaged. The particle board/chip board started to flake badly. I painted clear epoxy over the outside of the board to prevent further deterioration. The speaker company can replace the board. They are asking if I want particle board again or MDF. What would you go with for a replacement? If I go with MDF, I assume I should replace the other back on the other Symphony as well.

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Hey man,

Yes, buy that cotton batting and use that for your curtain. Keep as much as the original batting as you can, replace the bare minimum.

If they were mine, I'd make sure the backs are sealed with the clear epoxy. Any crazy missing portions of the flake board would get filled with epoxy filler. All gently sanded to make right. Then primed and painted black, add a vintage looking chrome handle at the top to assist in removing, install modern binding posts. If you don't want to bother, have new backs made with MDF and do the same mods as I just stated. The original flakeboard does get mealy over the decades, it's too bad. It's really good for acoustical projects. But after you soak it with epoxy, any deterioration has been taken care of and you can move on. MDF ain't cheap, I say try to keep it as original as you can.

Biggles
 
Hay,

Here's a back that I did what I suggested you do to yours. It's an early 1950's mono cabinet, approximately 10 cubic feet. The back was ugly, trashed, multiple extraneous holes, you get the idea. It's not that big of a deal to do, but it makes a world of difference. Especially the chrome handle. It makes safely removing the back tons easier.

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Biggles
 
Ok. Thanks for all the assistance so far. I have more questions.

You're welcome. S'ok, we got more answers.

As mentioned in thread #10, would this stuff work for the curtains?

I unfortunately cannot tell from that photo.

A number of online vendors sell a cotton batting product. I have not, alas, done business with any of them.

So I went digging around on the interwebs to see what looked like the original Bozak curtain.I think this one is very close:

I'm not suggesting you purchase those, just that this is the sort of cotton product which is suitable. The first link has a clearer photo.

The batting should not be too dense, like felt, but not too loose, like poly fiberglass. This is why upholstery batting is perfect for the lining and curtain.

If the other insulation is OK (not rotting or water damaged), can I keep it in the cabinet and not replace it?

Yes, provided it is not damaged, mildewed, etc.

One of the backs of the Symphony cabinets got water damaged. The particle board/chip board started to flake badly. I painted clear epoxy over the outside of the board to prevent further deterioration. The speaker company can replace the board. They are asking if I want particle board again or MDF. What would you go with for a replacement? If I go with MDF, I assume I should replace the other back on the other Symphony as well.

I fully concur with Biggles suggestions for the back. Penetrating epoxy is a wonderful resin to use, because it soaks in and delivers a smooth, sandable surface. The MDF will be solid and not prone to further disintegration.

I also suggest you fill in the screw holes in the back and re-drill them. This will provide a tighter fit which will not loosen as you put the backs on and off during your experimentation. Hopefully not more more then once, of course. I've drilled them out to be slightly larger and then filled them with resin.
 
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