Ha! No kidding on the flower pots. I'm all for one stop shopping. I think I'm good on wire. I have a few spools of different wire that I can choose from if I decide to re-wire. Guess I might as well while I'm in there.
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Bozak B4000 Symphony - Restoration - Seeking Advice
- Thread starter MATT0404
- Start date
Good catch!
Well, ya know, if you're going to make a mistake in a project, this would be a great way to do it. An inexpensive way to do it.
Biggles
Retrovert
Addicted Member
I definitely suggest you rewire. The old wire typically used vinyl inuslation which has long since hardened and become brittle. The original lifespan for vinyl wire was about thirty years for ordinary wire and fifty for the high-reliability wire used by AT&T for phone wiring. While the wire does not spontaneously disintegrate at some point, it does harden over time and is vulnerable to cracking when flexed.
Silver-plated teflon is not expensive and it is very nice wire, BTW.
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Retrovert
Addicted Member
Just to elaborate for the non-Bozak experts; the L-Pad replaces Tobin's fixed 7.5 Ω attenuator to allow variation to account for preferred volume level, hearing, room treatment, and personal taste.
You're right about that. I've made much more expensive mistakes in this hobby!
Thanks for the tip! Looks like a re-wire is in order.
Richard1079
Active Member
I have now 5 sets of b4000’s. My 62’s came without salad bowls. They survived 40 years without them. In talking to mr. betts, the and 800a can be damaged by the bouncing of the very low frequencies of the 199’s at very loud volumes only. Your talking about from 100hz down at high volumes. The .002 thin aluminum used in the 800a can’t always sustain that. Not sure how many people ever damaged an 800a? Anyone know of one being replaced? The 800 apparently was made of a thicker foil?
Regarding the xo configuration, I have tried a few. I found the total Tobin mod too drastic. It made trumpets and brasses sounds like a muted trumpet. I’ve tried diff values.... and I’m running different things in various speakers. Best solution might be to go with a-6 or 3 dB mod instead of the -9. If you have an equalizer just adjust to -5 dB in the 5000-10000 hz range if you find it grating your ears. I found the non reversed polarization brighter and preferred that. Also make sure to use the upper tabs of the coil connections. The explanation was too complicated for me but Judy can send you the literature on why to use the upper tabs.
Lastly insulate the tweeter box
Regarding the xo configuration, I have tried a few. I found the total Tobin mod too drastic. It made trumpets and brasses sounds like a muted trumpet. I’ve tried diff values.... and I’m running different things in various speakers. Best solution might be to go with a-6 or 3 dB mod instead of the -9. If you have an equalizer just adjust to -5 dB in the 5000-10000 hz range if you find it grating your ears. I found the non reversed polarization brighter and preferred that. Also make sure to use the upper tabs of the coil connections. The explanation was too complicated for me but Judy can send you the literature on why to use the upper tabs.
Lastly insulate the tweeter box
Retrovert
Addicted Member
Sigh.
What are you talking about? Your strawman is certainly on fire, but that's your strawman, not mine.
The issue of the midrange bell has never been any purported issue of "damage" to the driver, but cross modulation: pressure from the woofer backwave moves the midrange cone, causing the midrange driver to reproduce sound. The reverse can happen too, of course, i.e. midrange modulating the woofer, but it is less of a problem because of the low-pressure backwave from the midrange.
I've always been very clear about why a midrange cover is desirable. It has never been about damage. That is a ridiculous claim.
Your implication that I promoted the bell as a means to prevent damage to the midrange is absolutely false. Provide a single quote from this thread where I, or anyone else, made such a ridiculous claim. None of us are chasing that damage phantasm.
So it isn't that your drivers "survived" perfectly fine, it is that the sound quality is less than what could be achieved. Nobody here has ever claimed damage could result. I defy you to find a single example of that. It simply does not happen and nobody here claimed it would happen. I've never even seen such a claim.
The issue with midrange covers is cross-modulation distortion. A well-known issue in speakers going back to at least the 1950s.
Try the bell and your midrange clarity will improve. If you don't like the bell, use the flowerpots to plant basil.
Sigh.
I have repeatedly and routinely suggested using an L-Pad instead of Tobin's fixed attenuator, and specifically described why I feel his one-size-fits-none approach was used and why the L-Pad is superior. We all now do this. It's an obvious tweak and an easy one.
The actual attenuation value cannot be fixed for everyone, as it varies by tweeter type (B-200Y vs B-200Z), driver placement (speaker bracket vs. high up), number of drivers, position in the room, room characteristics, and type of music.
The L-Pad has become the consensus and everyone who has used it has been able to dial in the exact performance sought. Fixed value attenuators are sooooo last decade.
As far as "too drastic" are you referring to shifting the crossover point downwards to unload the woofer, which poorly reproduces in the midrange? I've never seen anyone say that was a "drastic" change which ruined the sound. Quite the opposite.
Backwards. Reversing the midrange is louder (aka "brighter" in audiophile speak) because it swaps the direction of the rarefaction and compression waves. Non-reversed is less forward. It removes distortion.
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cubby01
aka Buck
Hi all. Minor thread resurrection here...
I recently picked up a pair of B4000 Symphony. Don't know exactly when this pair were made. The drivers (all but one) date from '64 or '65. X overs labeled N-105. I'll be recapping soon as I get parts.
Driver complement per cabinet:
8 Tweets: b-200y (8ohm)
1 Mid: b-800a (8ohm)
2 Woofs: b-199a (mixed)
So here's the odd thing ... in each cabinet, one 199a is 16 ohm and the other is 8 ohm, wired parallel. Does anyone know if that may have been done for a reason? What would be the sonic affect vs the standard 2x16ohm woofers. One of the 8ohm is older (1961) and obviously a replacement (different screws, older style label).
I'll be on the lookout for replacement 16ohm woofers but until then I'm thinking of loading both 16 ohm in one cab so that at least one cab has it's the normal configuration. And then putting both 8 ohm in the other cab - But only wiring up one of them. It's hopefully a temporary solution. What do y'all think, yea or nea?
Oh, last question. What size flower pot for the mid cover? The original salad bowl cover is all broken to pieces.
-Buck
I recently picked up a pair of B4000 Symphony. Don't know exactly when this pair were made. The drivers (all but one) date from '64 or '65. X overs labeled N-105. I'll be recapping soon as I get parts.
Driver complement per cabinet:
8 Tweets: b-200y (8ohm)
1 Mid: b-800a (8ohm)
2 Woofs: b-199a (mixed)
So here's the odd thing ... in each cabinet, one 199a is 16 ohm and the other is 8 ohm, wired parallel. Does anyone know if that may have been done for a reason? What would be the sonic affect vs the standard 2x16ohm woofers. One of the 8ohm is older (1961) and obviously a replacement (different screws, older style label).
I'll be on the lookout for replacement 16ohm woofers but until then I'm thinking of loading both 16 ohm in one cab so that at least one cab has it's the normal configuration. And then putting both 8 ohm in the other cab - But only wiring up one of them. It's hopefully a temporary solution. What do y'all think, yea or nea?
Oh, last question. What size flower pot for the mid cover? The original salad bowl cover is all broken to pieces.
-Buck
Hey Cubby,
Welcome to the Bozak corner. Congratulations on your score, nice action. You really scored with the B-800A mids. Those are aluminum cone 8" midrange drivers and coupled with the B200Y array will give you a spine tingling response all on their own, even without a woofer. I remember sitting there while working on my Symphony project. I had just the mids and the tweeters running for a little while, they're that good.
As you already know, you have 2 issues. The crossovers need new caps, you got a fungle of 8 and 16ohm B199's. Your amplifier is seeing a tough load with the 8ohm woofer in there, it's not right. It's even from right to left, but not right. You can find 16ohm replacements on ebay. But you have to setup a Saved Search. It might take a few months, or 2 years. And, they can be about double of the cost of the 8ohm version, be prepared. I say, bull#$%^^^. You don't need 2 woofers per cabinet. In fact, I'd be willing to bet you a pound of bacon you'd probably prefer just one. I ran my Symphony project with 1 B199 woofer per cabinet. To me, it sounded more coherent, cleaner. And, it dug a little deeper than having a pair. You see, it is advertised that the Symphony cabinet is 8 cubic feet. But the 2 pairs I had, I measured them out to 6.9 cubic feet. We know Bozak B199's want a minimum of 8 cubic feet for 2 woofers, and you don't have that. So, put 1 12" woofer in 6.9 cubic feet and you have a thunderous monster on your hands! Get yourself some 3/4" plywood and cut yourself a cover for the bottom woofer holes in your cabinets. Paint the fronts black, drill holes where the woofer's mounting holes are and mount them that way. A little leaky is okay, but you can gently caulk from the inside if that makes you crazy. Remember, cover the bottom woofer holes. This setup was actually a possible configuration from Bozak directly, so you're not going outside factory correct. You have older woofers, back when everyone had tube amplifiers. They will not take the power of the later 1960's woofers do. So, be judicious in your volume knob turning.
Each crossover will take 1 50uf cap for the mid, and I think an 8.2uF cap for the tweeters. I suggest ordering Dayton Audio 5% from parts express. Yes, you can spend hundreds on caps, but that's ridiculous and unnecessary. I also suggest you do 2x25uF caps for your 50uF, wired in parallel. Yes, you can do the Tobin 104T mod for your crossovers. Since you have the N-105 crossover 98% of that process has already been done. All you need is the tweeter leg design from Pat's 104T schematic. The 104T schematic is online somewheres. What Pat's design does is add a Zobel Network. This tames the audible 7k impedance hump in the B200Y tweeters. It makes the old tweeters smooooother. It's up to you how you'd like to proceed.
If they were mine, I'd sell off all the B199's you have and buy 2 later 1960's 8ohm B199's and only put 1 per cabinet. New caps for the crossovers and I'd probably remove all the Bozak tweeters and get a modern solution. Right now on my Bozaks I use a SEAS Excel T25. Soon, I will wire up my brand new ESS Heil tweeters and see what they're like on Bozaks. I bought a pair on sale from the factory, oh yes.
Biggles
Welcome to the Bozak corner. Congratulations on your score, nice action. You really scored with the B-800A mids. Those are aluminum cone 8" midrange drivers and coupled with the B200Y array will give you a spine tingling response all on their own, even without a woofer. I remember sitting there while working on my Symphony project. I had just the mids and the tweeters running for a little while, they're that good.
As you already know, you have 2 issues. The crossovers need new caps, you got a fungle of 8 and 16ohm B199's. Your amplifier is seeing a tough load with the 8ohm woofer in there, it's not right. It's even from right to left, but not right. You can find 16ohm replacements on ebay. But you have to setup a Saved Search. It might take a few months, or 2 years. And, they can be about double of the cost of the 8ohm version, be prepared. I say, bull#$%^^^. You don't need 2 woofers per cabinet. In fact, I'd be willing to bet you a pound of bacon you'd probably prefer just one. I ran my Symphony project with 1 B199 woofer per cabinet. To me, it sounded more coherent, cleaner. And, it dug a little deeper than having a pair. You see, it is advertised that the Symphony cabinet is 8 cubic feet. But the 2 pairs I had, I measured them out to 6.9 cubic feet. We know Bozak B199's want a minimum of 8 cubic feet for 2 woofers, and you don't have that. So, put 1 12" woofer in 6.9 cubic feet and you have a thunderous monster on your hands! Get yourself some 3/4" plywood and cut yourself a cover for the bottom woofer holes in your cabinets. Paint the fronts black, drill holes where the woofer's mounting holes are and mount them that way. A little leaky is okay, but you can gently caulk from the inside if that makes you crazy. Remember, cover the bottom woofer holes. This setup was actually a possible configuration from Bozak directly, so you're not going outside factory correct. You have older woofers, back when everyone had tube amplifiers. They will not take the power of the later 1960's woofers do. So, be judicious in your volume knob turning.
Each crossover will take 1 50uf cap for the mid, and I think an 8.2uF cap for the tweeters. I suggest ordering Dayton Audio 5% from parts express. Yes, you can spend hundreds on caps, but that's ridiculous and unnecessary. I also suggest you do 2x25uF caps for your 50uF, wired in parallel. Yes, you can do the Tobin 104T mod for your crossovers. Since you have the N-105 crossover 98% of that process has already been done. All you need is the tweeter leg design from Pat's 104T schematic. The 104T schematic is online somewheres. What Pat's design does is add a Zobel Network. This tames the audible 7k impedance hump in the B200Y tweeters. It makes the old tweeters smooooother. It's up to you how you'd like to proceed.
If they were mine, I'd sell off all the B199's you have and buy 2 later 1960's 8ohm B199's and only put 1 per cabinet. New caps for the crossovers and I'd probably remove all the Bozak tweeters and get a modern solution. Right now on my Bozaks I use a SEAS Excel T25. Soon, I will wire up my brand new ESS Heil tweeters and see what they're like on Bozaks. I bought a pair on sale from the factory, oh yes.
Biggles
PS - Yes, those original mid covers are about as strong as broken egg shells. You want a plastic flower pot that fits. I know an 8" flower pot goes over the smaller 6" Bozak mid. But maybe a 10" flower pot for the B-800A. You don't need a lot. Line inside and outside with 1" 100% cotton upholstery batting.
Biggles
Biggles
Retrovert
Addicted Member
To follow up on Biggle's excellent post, you must consider the effect of using the wrong impedance.
The woofer's crossover point is determined by the formula involving inductance and impedance.
The crossover frequency for an inductor is calculated as:
So the crossover point is now downwards moved.
Here's the calculations. One could just use my scaling factor, but let's do the math.
If the LOWER woofer-midrange crossover is used point this shifts from:
If the HIGHER woofer-midrange crossover is used:
In either case a giant hole has been inserted between the midrange and the woofer. The fact that this is a first-order crossover, with 6 dB / octave slopes, allows the rolloff to somewhat cover this hole, but it's going to sound peculiar.
The math will not lie to you, unlike the interwebs.
TL/DR: Don't use an impedance other than the value for which the crossover was designed.
The woofer's crossover point is determined by the formula involving inductance and impedance.
The crossover frequency for an inductor is calculated as:
f = R / (2 x π x L)
we can see that when the denominator (inductor) is held constant but the numerator (speaker impedance) changes from 8 Ω (16 Ω || 16 Ω) to 5.33 Ω (8 Ω || 16 Ω) then the frequency will shift by 8 / 5.33 = 150%.So the crossover point is now downwards moved.
Here's the calculations. One could just use my scaling factor, but let's do the math.
If the LOWER woofer-midrange crossover is used point this shifts from:
f = R / (2 x π x L)
= 8 / (2 x π x 0.00315)
= 404 Hz
to= 8 / (2 x π x 0.00315)
= 404 Hz
f = R / (2 x π x L)
= 5.33 / (2 x π x 0.00315)
= 270 Hz
= 5.33 / (2 x π x 0.00315)
= 270 Hz
If the HIGHER woofer-midrange crossover is used:
f = R / (2 x π x L)
= 8 / (2 x π x 0.00158)
= 806 Hz
to= 8 / (2 x π x 0.00158)
= 806 Hz
f = R / (2 x π x L)
= 5.33 / (2 x π x 0.00315)
= 534 Hz
= 5.33 / (2 x π x 0.00315)
= 534 Hz
In either case a giant hole has been inserted between the midrange and the woofer. The fact that this is a first-order crossover, with 6 dB / octave slopes, allows the rolloff to somewhat cover this hole, but it's going to sound peculiar.
The math will not lie to you, unlike the interwebs.
TL/DR: Don't use an impedance other than the value for which the crossover was designed.
Retrovert
Addicted Member
Sorry to be the bearer of bad news, but you have the midrange which requires a latex-foam ring to damp cone ringing. Your foam has degraded (or is missing) which means your driver clarity is sub-standard. This ring cannot be easily reproduced, and I know of no one who has successfully done it. The first version of the aluminum-cone B-209 was the A and the surround was redesigned to perform damping. The drivers have the same appearance but not the same sound. (The straight B-209 with no suffix is a paper-cone.)
A new pair of midranges will run you about $100 delivered. Be certain to purchase the 8 Ω variety; some unscrupulous sellers will try to sell you a 16 Ω, even going to the point of removing the the impedance marking. The same goes for the model number, as "A" units are disguised as others. Do not purchase any midrange which lacks the Bozak impedance and full model number.
The B is alnico, while the Bc and C are ferrite. The difference between the Bc and C is that the Bc is only rear mount and the C is front or rear mount; the two are otherwise identical ceramic magnet version of the B-209B alnico.
TL/DR: I suggest replacing with a B, Bc, or C midrange.
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Retrovert
Addicted Member
One more thought.
The dual woofer units may not converge in a smaller space. Biggles above detailed his Symphony experience. This should be heeded. You have no idea how much trouble was required to find four 16 Ω B-199 drivers. Those drivers are uncommon and expensive, so if you sell your pair it will be expensive to back out of that decision. On the plus side, it will pay for all of the other upgrades.
You may be happier with a single-woofer configuration where the woofer and midrange are as close as possible for better convergence.
Not sayin', just sayin'.
The dual woofer units may not converge in a smaller space. Biggles above detailed his Symphony experience. This should be heeded. You have no idea how much trouble was required to find four 16 Ω B-199 drivers. Those drivers are uncommon and expensive, so if you sell your pair it will be expensive to back out of that decision. On the plus side, it will pay for all of the other upgrades.
You may be happier with a single-woofer configuration where the woofer and midrange are as close as possible for better convergence.
Not sayin', just sayin'.
cubby01
aka Buck
Nah, this is the 800a mid, not the 209a mid. No foamy damping in this puppy.
Thanks to you and Biggles for replies.
These have what i find to be a really oddball xover, not only with the reversed polarity mid but the way the tweeter network common seems to run through the mid filter. At first i thought it was a builder mistake but I've seen (virtually) with several b4000s that have the b800a mid and b200y tweeters.
I still have some reservation about just ignoring this and doing the n104t mod. You know, in case theres some secret sauce at play for this particular midrange tweeter combo.
Redarding the woofs, since i have two 16 ohm and two 8 ohm I'm going to load one with a pair of 16s and load the other with a single 8 and see if the double 16s are worth chasing down two more.
These will go into a 20x16 room w 9ft ceiling
Thanks again for your time.
Retrovert
Addicted Member
Arrgh!. Yes, I see that. I am so primed to warn people off the B-209A that I misread that in the context of midrange. I now remember you have the B-800A midrange. Sorry about that.
Hmmm.
If the tweeter was tapped from the midrange bandpass then it would, of necessity, be running in the same frequency band as the bandpass. The inductor would limit the maximum frequency. I doubt this is a series crossover as that was not used by Bozak.
Could the wiring be using the same attachment point to permit bi-amping? The bi-amping kit is the N-106 active splitter (generates high/low for the two amplifiers) and an N-107 passive crossover to split the midrange/tweeter.
Have a schematic?
Trace out the wiring. You can always restore it.
The main advantage of using a straightforward crossover is replacement the tweeters with a soft-dome, or cut the cone tweeters at, say, 8k Hz and switch to a soft dome at that point.
Bozak tweeters are great for their timeframe, but we have better options for the high end.
It's a good experiment. You may find you prefer the single woofer. Experiment with the convergence.
The advantage of dual vertical drivers is it tends to remove some of the issues with where the listener's ears are in the vertical plane.
How far away are you sitting? Biggles found that he had to cram himself against his rear wall to get the sound to converge. I have had similar experience with speakers having a long convergence point.
You're welcome. No Bozak Left Behind.
cubby01
aka Buck
Not a schematic per se but this will do. It's the orange wire between the two resistors in the Cap box that I didn't understand the purpose of. My knowledge is lacking but looking at it now I'm thinking the 5mf in parallel with the top 25R is a contour for the tweeters then it's using the lower 25R as an attenuation. ?
After I drew it up I realized the OP has the same driver line up and x-over network that I do.
Same model ugly paddle front too.
(This is how I saw them at an estate sale. Bought them without even asking if they worked.
)
Attachments
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cubby01
aka Buck
<Chuckle>. Tell my wife that.
She liked the sound by the way, even before any updates. She also asked if they could be stacked, you know,like if we had four of them....