Bozak Crossover update - 16 ohm version?

[John_Doe1987]

Hello all,

I've been doing my due diligence trying to read up on the many musings posted here about what should be done about old Bozak crossovers. I've gathered that I ideally want to make a few changes to the crossovers themselves besides simply recapping the system.

1) Shift the low-pass crossover points from 800 to 400hz
2) Shift the high end of the band-pass filter from 2.5 to 1.25 khz (so the mid-range transitions nicely into the tweeters)
3) Add a Zobel network and L-pad attenuator to tame the non-linear response and spike ~10khz of the b-200y tweeters.

In researching all of this I've only found documentation (so far) on 8 ohm systems. Now I have the 16 ohm variation of the b-199a woofers and recently bought a pair of b209bc (16ohms) so I would like to stick to 16 ohms of impedance for these speakers.

My question is this: what components do I need to achieve the three aforementioned goals. I have all sorts of diagrams, schematics and parts lists for the updates, but they are all for 8 ohm systems. Any guidance or wisdom would be much appreciated!

Thanks,

John

 

[John_Doe1987]

Below is the original crossover specifications. I've been trying to use LTSpice to model the crossover and then use the T/S parameters to figure out the values myself, but to no avail so far.

 

[drbiggles]

I’ll be back later if nobody jumps in.

Biggles

 

[drbiggles]

John, How many woofers you got? Sounds like you have 4 16ohm woofers. If you wire those in parallel you get an 8ohm load, do that. That's the 3.15mH (+side #2) inductor for the woofer on an 8ohm load. Put a 25uF cap on your 16ohm mid (- side #1 side) to bring it in at 400hz to match the woofer. You want a 2mH inductor on the + side (#2 side) of the 16 ohm mid. As lon.g as you do a pair or quad of B200Y's, you can load them as 8ohms and go with an 8uf cap. You mentioned wanting to go with a zobel. Which is a good idea if you can build a notch filter at 7hz or 10hz . only, otherwise your Zobel is going to smooth all your frequencies down. After some listening time, it just doesn't sound right, you need some zippety in your doo dah. Try it without the zobel first. Just do the cap and 8ohm l-pad, that's the best way to go about it.

Biggles

 

[John_Doe1987]

John, How many woofers you got? Sounds like you have 4 16ohm woofers. If you wire those in parallel you get an 8ohm load, do that. That's the 3.15mH (+side #2) inductor for the woofer on an 8ohm load. Put a 25uF cap on your 16ohm mid (- side #1 side) to bring it in at 400hz to match the woofer. You want a 2mH inductor on the + side (#2 side) of the 16 ohm mid. As lon.g as you do a pair or quad of B200Y's, you can load them as 8ohms and go with an 8uf cap. You mentioned wanting to go with a zobel. Which is a good idea if you can build a notch filter at 7hz or 10hz . only, otherwise your Zobel is going to smooth all your frequencies down. After some listening time, it just doesn't sound right, you need some zippety in your doo dah. Try it without the zobel first. Just do the cap and 8ohm l-pad, that's the best way to go about it.

Biggles

1. I apologize for any confusion with my wording. I have two (2) b199-A woofers total. That's one (1) per cabinet. Considering I now have a pair (2) B209-bc mids, my inclination would be to run a 16 ohm system.

2. Could you explain the use and implementation of the L-pad attenuator in the tweeter circuit? I found Retrovert's thorough breakdown of the Tobin modification but, to my best recollection, he lumps the L-pad attenuator and Zobel network together as solutions to the non-linear response of the 200ys. I'm inclined to take your suggestion about waiting on a Zobel network, but in that case what would the l-pad do? How would I add it?

3. Considering point #2, the only other modifications to component values would be the inductor (noted currently as 3.15 Mega (?) Henrys to achieve a 800hz xo point) in the woofers circuit and the caps (10 uf and 5uf in parallel) for the high xo of the band-pass filter to shift the cutoff frequency from 2500 to 1250. What would those new values be?

4. I have seen many references to people "bypassing" the prop caps with tiny (0.01uf or similar) film caps to improve response - is this important?

5. I have a rather small cabinet that houses the woofer and one (1) set of b-200y's. By my measurement the volume is ~5.25 ft3 externally and ~4 internally. These are custom cabinets from a previous owne and lack the curtain part of the infinite baffle design. Is it worthwhile to add the curtain if the cab is already too small for the woofers? Or does it (either the size of the cab or the curtain) not matter?

I'm sure I'll be back with more questions - thanks in advance!

John

 

[drbiggles]

1. I apologize for any confusion with my wording. I have two (2) b199-A woofers total. That's one (1) per cabinet. Considering I now have a pair (2) B209-bc mids, my inclination would be to run a 16 ohm system.

Put a 6.37 milli Henry inductor on the + side of the woofer. Or as close to that value as you can, 6.0 is fine, 6.2.

You could run 1 16ohm tweeter, but 8ohm lpad won’t adjust frequency correctly because it’s a 16ohm load. You won’t find a 16ohm lpad. I suggest running a pair of 200y tweeters and keep it 8ohms.

2. Could you explain the use and implementation of the L-pad attenuator in the tweeter circuit? I found Retrovert's thorough breakdown of the Tobin modification but, to my best recollection, he lumps the L-pad attenuator and Zobel network together as solutions to the non-linear response of the 200ys. I'm inclined to take your suggestion about waiting on a Zobel network, but in that case what would the l-pad do? How would I add it?

Instructions are in the lpad box, follow those. It’s easy.

3. Considering point #2, the only other modifications to component values would be the inductor (noted currently as 3.15 Mega (?) Henrys to achieve a 800hz xo point) in the woofers circuit and the caps (10 uf and 5uf in parallel) for the high xo of the band-pass filter to shift the cutoff frequency from 2500 to 1250. What would those new values be?

You said you wanted 400hz, that’s what I gave you values for. Which crossover points do you want?

4. I have seen many references to people "bypassing" the prop caps with tiny (0.01uf or similar) film caps to improve response - is this important?

If you’re running electrolytic caps, you can bypass with film or poly. But if you’re running film or poly, you cannot bypass with film or poly. All that does is jack your values by .01 uF. I like using electrolytic.

5. I have a rather small cabinet that houses the woofer and one (1) set of b-200y's. By my measurement the volume is ~5.25 ft3 externally and ~4 internally. These are custom cabinets from a previous owne and lack the curtain part of the infinite baffle design. Is it worthwhile to add the curtain if the cab is already too small for the woofers? Or does it (either the size of the cab or the curtain) not matter?

I'm sure I'll be back with more questions - thanks in advance!

John

You need the woofer to have from 2 cubic feet to 10cubic feet. If you have less, you need new cabinets. You must have the curtain, that’s KEY.

Biggles.

 

[John_Doe1987]

Put a 6.37 milli Henry inductor on the + side of the woofer. Or as close to that value as you can, 6.0 is fine, 6.2.

You could run 1 16ohm tweeter, but 8ohm lpad won’t adjust frequency correctly because it’s a 16ohm load. You won’t find a 16ohm lpad. I suggest running a pair of 200y tweeters and keep it 8ohms.



Instructions are in the lpad box, follow those. It’s easy.



You said you wanted 400hz, that’s what I gave you values for. Which crossover points do you want?



If you’re running electrolytic caps, you can bypass with film or poly. But if you’re running film or poly, you cannot bypass with film or poly. All that does is jack your values by .01 uF. I like using electrolytic.



You need the woofer to have from 2 cubic feet to 10cubic feet. If you have less, you need new cabinets. You must have the curtain, that’s KEY.

Biggles.

Thank you for the insight. Let me clarify a couple things.

The desired crossover points are 400hz for the woofers and 1250 hz for the high cutoff for the mid-ranges. That's what I've seen been recommended.

I see you mentioned changing the stock inductor from 3.15 MH to ~6.37 MH - that makes sense.

What would the difference in capacitance be for the caps in the band pass leg of the filter? The stock xo has 15uf total, achieving a cutoff of 2500 hz. What would the values of the cap(s) need to be to achieve the desired 1250hz cutoff?

Forgive me if this is a silly question, but I thought that speaker systems have to have a common load, e.g all drivers run at 8 OR 16 ohms (or anything else for that matter). How can I mix and match those impedances?

 

[drbiggles]

Thank you for the insight. Let me clarify a couple things.

The desired crossover points are 400hz for the woofers and 1250 hz for the high cutoff for the mid-ranges. That's what I've seen been recommended.

I see you mentioned changing the stock inductor from 3.15 MH to ~6.37 MH - that makes sense.

What would the difference in capacitance be for the caps in the band pass leg of the filter? The stock xo has 15uf total, achieving a cutoff of 2500 hz. What would the values of the cap(s) need to be to achieve the desired 1250hz cutoff?

I gave that to you earlier, I aimed for 1250 in the band pass or somewhere in there.

Forgive me if this is a silly question, but I thought that speaker systems have to have a common load, e.g all drivers run at 8 OR 16 ohms (or anything else for that matter). How can I mix and match those impedances?

I’m assuming you have a solid state amplifier you can use, it handles mismatched loads. Remember, that 16ohms nominal or 8ohms nominal is just a wild guess. Sometimes speaker systems go down to 1ohm. And, we’re rebels. We break rules. I’ve done similar crossovers to this for customers. 16ohm mids, it’s what they have. We’re not all rich. So far, no complaints. We do the best we can with what we have, it works fine.

Biggles

 

[drbiggles]

Besides, if you don’t like something, change it.

Biggles

 

[John_Doe1987]

I gave that to you earlier, I aimed for 1250 in the band pass or somewhere in there.



I’m assuming you have a solid state amplifier you can use, it handles mismatched loads. Remember, that 16ohms nominal or 8ohms nominal is just a wild guess. Sometimes speaker systems go down to 1ohm. And, we’re rebels. We break rules. I’ve done similar crossovers to this for customers. 16ohm mids, it’s what they have. We’re not all rich. So far, no complaints. We do the best we can with what we have, it works fine.

Biggles

Thank you very much for all the help! Your advice is much appreciated.

 

[John_Doe1987]

Just wanted to tie off with a parts list for the xo (for as much my benefit as anyone else who stumbles across this thread)

Woofer (low pass): Cutoff frequency of 400hz. Change the stock 3.15 MH inductor to ~6.37 MH.

Mid-range (bandpass): Cutoff frequency of 1250 and 400hz (is it 400? I thought the mid was left at 800hz to create an even roll off to the woofer... But you're probably correct!). Replace the stock 15uf cap with a 25uf capnand the stock 1.1 MH inductor for a 2MH inductor.

Tweeter (high pass): No change besides the L-pad attenuator (refer to box for directions).

Is the above correct?

Best,

John

 

[drbiggles]

Hay,

Yeah, pretty much. Except you want both woofer and mid to meet at 400. It’s the mids top end that gets cut off early at 1250 and neatly slides into 2500hz.

Biggles

 

[John_Doe1987]

Hay,

Yeah, pretty much. Except you want both woofer and mid to meet at 400. It’s the mids top end that gets cut off early at 1250 and neatly slides into 2500hz.

Biggles

Sounds good! I have everything in my parts express cart save for the L-pad. There are several different models with varying diameters and watt-ratings. Which should I go for? They also list 16 ohm L-pads which I thought you mentioned were not made (and was the reason for the 8ohm tweeter leg).

TL;DR, which do I buy?

Thanks again,

John

 

[drbiggles]

Sounds good! I have everything in my parts express cart save for the L-pad. There are several different models with varying diameters and watt-ratings. Which should I go for? They also list 16 ohm L-pads which I thought you mentioned were not made (and was the reason for the 8ohm tweeter leg).

TL;DR, which do I buy?

Thanks again,

John

Oh cool! I’d not seen a 16ohm lpad at parts express, nice. Now we need a 4 ohm version.

You want the 8ohm 15watt mono with the 1” post. Should be like $12 or so. That’s a year ago price. That’ll do it.

Biggles