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Need help with 2-Way passive crossover design for some Zilch eWave precursors

BmWr75

BmWr75

Top octave? pfffffftttttt
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Hey Guys,

Back in April 2008 I met Zilch here on AK when I asked for speaker design help in this thread. Here is a link to the finished speaker pictures.

I stayed in touch with Zilch until a couple of months before he passed way, but we never got around to designing a passive crossover for the speakers. They have always been biamped using an active Behringer crossover.

Still looking for help to design a good passive crossovers for these speakers. I can build them if someone can tell me what discrete components to use and draw the circuit.

They use a BMS 4555 compression driver connected to a JBL PT-D95HF horn. The woofers are JBL 127H-1. The cabinets are Heath AS-10s with these dimensions 24" tall x 13.5" wide x 11.5" deep. The active crossover point is set at ~1.8 kHz.

Was always hoping one of the crossover designs Zilch was working on at Parts Express TechTalk forum would work: http://techtalk.parts-express.com/sh...d.php?t=215536 There is already a Project 12 listed there that uses the BMS 4555 driver, but a different JBL waveguide and Altec woofer.

Any help designing an outboard passive crossover so I could use the speakers more often would be greatly appreciated.
 
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@4343 - in the another thread you responded as shown below. I don't understand your question about the "comp filter", please explain.

4343 said:
I'd start with one that was for something similar, like this one:

http://audiokarma.org/forums/showpost.php?p=2434268&postcount=128

Since you have them bi-amped now, you can just Zilch-nut together the circuit outside the box to try out. Compare it to the other still bi-amped one, and see if you like it enough to build another.

BTW, the details of the comp filter you are using were never included in our thread. If you could post those details it might be helpful. Basically, all you need is the 1.8KHz crossover function added to your compensation circuit.

I have been using a similar setup, but using the threaded version and Selinium D2500Ti driver, for a while now. I'll have to check my notebook for the circuit I used.
Click to expand...
 
@4343 - my long-term memory came back. :D

The comp filter I'm using is a Linkwitz-Riley with a slope of 24 dB/octave. The crossover point between the woofer and tweeter is set at 1.6 kHz.

Had to get the DCX2496 manual out of determine this. I set it up long ago and haven't touched it since.
 
BmWr75 said:
@4343 - my long-term memory came back. :D

The comp filter I'm using is a Linkwitz-Riley with a slope of 24 dB/octave. The crossover point between the woofer and tweeter is set at 1.6 kHz.

Had to get the DCX2496 manual out of determine this. I set it up long ago and haven't touched it since.
Click to expand...

That's the crossover filter. The compensation filter is mentioned here:

http://audiokarma.org/forums/showpost.php?p=1874260&postcount=23

In the following post:

http://audiokarma.org/forums/showpost.php?p=1874483&postcount=24

Zilch called it a "Balanced-T" compensation filter. I'm assuming this is what is inside your cabinet, feeding the compression driver.

Compensation, or pre-compensation sometimes, is "boosting" the HF over the midrange to counter-act the falling response of the compression driver when mounted on the wave guide. (The "boost" is actually attenuation of the midrange, not a boost of the HF at all.)
 
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I had to clean out my PMs a while back because they hit the AK limit. Don't still have the PM to which Zilch referred. Will have to open up one of these speakers and see what the capacitor and resistor values are. Will report back later.
 
BmWr75 said:
I had to clean out my PMs a while back because they hit the AK limit. Don't still have the PM to which Zilch referred. Will have to open up one of these speakers and see what the capacitor and resistor values are. Will report back later.
Click to expand...

That is good news, that the pre-comp is built in the box. I notice that your pic of the circuit is labeled as "small", maybe you have the original large pic, and can read the values that way?

Can you describe what the L-Pad does? If it is simply raising/lowering the HF level or something else?

Unless your drivers sensitivity matches very well you will need some way of matching the HF output to the woofer, usually this means padding down the HF. Having an L-Pad that does this already would make this simpler, but if, as I suspect, the variable resistor is there to allow you to adjust the amount of HF compensation, you will need to change things a bit. The simplest way would be to just add another L-Pad in front of your comp filter, after the crossover filter (that you will need to build). A bit more involved method would be to measure the value of the current L-Pad and replace it with a fixed resistor of the same value, thus freeing up the nicely mounted L-Pad to act as a level control for the HF.
 
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Balanced T = Z19

In searching for the term "Balanced T" I came upon this thread (again):

http://audiokarma.org/forums/showthread.php?t=328530

With this schematic/parts list:

http://audiokarma.org/forums/showpost.php?p=4086331&postcount=15

I appears Zilch did design a passive network for your horn/driver combo after all. :thmbsp: If you check the last page, Jack Giff is making circuit boards to make construction very easy!

Here is the graph (from page 1):

http://www.audiokarma.org/forums/attachment.php?attachmentid=236507&stc=1&d=1287719982

This page mentions a "spike killer" that he added for the BMS 4550:

"[W/BMS spike-killer notch across the driver = 0.15mH, 0.47uF, 2R7.]"

I'd bet that the values of the parts in our box match the ones in the schematic above, 6uf, 4ohm, 4ohm, and 2 ohm, plus the 30 ohm section of the L-Pad as mentioned in your thread.
 
Good eyes there @4343.

I found the full resolution picture and can read all three resistors, but not the capacitor.

From far left to right in the picture posted above: 4 ohm/10watt, 4 ohm/10watt, 2 ohm/10watt

The L-pad just raises and lowers the HF as best I remember. It is only connected to the compression driver. I was hoping I could log into Parts Express and look at my order history to find out the L-pad specifications, but my history there only goes back to December 2008. The writing on the back of the L-pad is "L-8 ohm WWP 100". The "100" part looks like part of the label that is smeared, so am not sure that is what is says. My guess is it is a 100 watt mono 3/8" shaft 8 ohm L-pad http://www.parts-express.com/pe/showdetl.cfm?Partnumber=260-262

On the back of the speaker I wrote -2 dB for the minimum setting and +2 dB for the maximum setting. Zilch would have had to told me that was the adjustment range.

I found Zilch's post about the comp filter, he said:

"L-Pads are not symmetrical; the resistance between terminals 1 and 2 varies from 0 to ~30 ohms, then none, with clockwise rotation, while that between terminals 3 and 2 varies from 8 ohms to zero.

This application uses the "parallel" leg, between terminals 1 and 2. On the front side of the L-Pad, the terminal numbers are embossed in the plastic, so tiny I need a magnifier to read them.

It appears that you have constructed the "Balanced-T" compensation filter correctly.... "

4343 said:
That is good news, that the pre-comp is built in the box. I notice that your pic of the circuit is labeled as "small", maybe you have the original large pic, and can read the values that way?

Can you describe what the L-Pad does? If it is simply raising/lowering the HF level or something else?

Unless your drivers sensitivity matches very well you will need some way of matching the HF output to the woofer, usually this means padding down the HF. Having an L-Pad that does this already would make this simpler, but if, as I suspect, the variable resistor is there to allow you to adjust the amount of HF compensation, you will need to change things a bit. The simplest way would be to just add another L-Pad in front of your comp filter, after the crossover filter (that you will need to build). A bit more involved method would be to measure the value of the current L-Pad and replace it with a fixed resistor of the same value, thus freeing up the nicely mounted L-Pad to act as a level control for the HF.
Click to expand...
 
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So, the fact that I'm using a different woofer doesn't matter? :dunno:

This crossover was designed for an Altec 414Z woofer and I'm using a JBL 127H-1 woofer.

I PMed JackGiff about the PCBs.

4343 said:
In searching for the term "Balanced T" I came upon this thread (again):

http://audiokarma.org/forums/showthread.php?t=328530

With this schematic/parts list:

http://audiokarma.org/forums/showpost.php?p=4086331&postcount=15

I appears Zilch did design a passive network for your horn/driver combo after all. :thmbsp: If you check the last page, Jack Giff is making circuit boards to make construction very easy!

Here is the graph (from page 1):

http://www.audiokarma.org/forums/attachment.php?attachmentid=236507&stc=1&d=1287719982

This page mentions a "spike killer" that he added for the BMS 4550:

"[W/BMS spike-killer notch across the driver = 0.15mH, 0.47uF, 2R7.]"

I'd bet that the values of the parts in our box match the ones in the schematic above, 6uf, 4ohm, 4ohm, and 2 ohm, plus the 30 ohm section of the L-Pad as mentioned in your thread.
Click to expand...
 
Z19 seems pretty universal

BmWr75 said:
So, the fact that I'm using a different woofer doesn't matter? :dunno:

This crossover was designed for an Altec 414Z woofer and I'm using a JBL 127H-1 woofer.

I PMed JackGiff about the PCBs.
Click to expand...

There's nothing special about the LF portion of the Z19. Reading through the thread, there are lots of different woofers and horn/driver combos being used with it. So you will have to try it and see if it sounds as good as your bi-amp setup.

As it is, your current setup does "nothing special" to your woofer either...
 
Guys hi
My name is Harel and just now got me a pair of Altec 19 Boxes and drivers.. Obviously, i need a pair of crossovers and while looking i encountered this interesting forum...
I used a bi-amp system to check the sound prior to building crossovers. i found that 1200~1500Hz is the most pleasant region
To my calculation on Zilchs' (MHRIP) design on the Woofer cutover point show 680Hz rather than the original N1201 Cross which suppose to cut over at 1200Hz? am i wrong here? My 416 and Tweeter are both 8Ohms BTW..
Thanks Harel
 
I suggest you start a new thread with your question. It would probably get more attention.

FYI - this project ended up being a bust for me. The JBL woofer sensitivity was way off for the crossover I built. A $200 learning for me.
 
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