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Heresy Crossover Mod - Less Bright


JohnA
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John, thanks for the schematic, BTW!

Notice the multipliers for the taps? I think that's the key where PWK is telling us how to use that autoformer to change the spectral balance of the Heresy to suit the installation.

"One step reduces the output 3 dB and doubles the impedance seen by the amp."

Yes I agree that one step reduces output by 3db but I don't think that it doubles what the amp sees. The amp sees the impedance of the entire system, woofer, tweeter and crossover.

What matters is that we've changed the impedance seen by the first 2uf cap that feeds the autoformer. By moving the taps, we've doubled the impedance, as you said.

That's the balance that needs to be restored. So we need to calculate the original impedance seen by that cap, then add the appropriate resistor across the autoformer.

The impedance seen by that first 2 uf cap is the impedance of the tweeter (8 ohms multiplied by the "tap factor" 8x4=32ohms) in parallel with that of the squawker (16 ohms multiplied by the "tap factor" 16x8=128 ohms). A 32 ohm impedance in parallel with 128 ohm impedance = 25.6 ohms

Double the 25.6 = 51.2 ohms seen by the cap. Parallel that with 51.2 ohms to bring the total seen by the cap back to 25.6.

I think this is roughly what AL K. was talking about...

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about the only issue not addressed by my ALKs was that while I could adjust the mid horn I could not adjust the tweeter horn. I found that when the ideal balance between mid and bass was reached the tweeter was still just a tad hot for my taste. so I ended up bumping the mid up a smidge from where I liked it to blend better with the tweeter level. leaving the bass behind...oh well, that is life...if anyone knows how I could bring the tweeter alone down just a tad I could back off the mid, et voila! my perfect levels. tony

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Huh?

The first cap essentially sees the impedance of the squawker multiplied by the autoformer, or 128 ohms at 700 Hz. If you drop it another tap the impedance goes to 256 ohms. Paralleling the squawker with a 16 ohm resistor makes the squawker appear to be 8 ohms and shows the first cap 128 ohms again. That makes the crossover work as it always did.

The 8 ohm tweeter will have an impedance of about 144 ohms at the squawker's crossover point, thus having little effect on the impedance seen by the first cap.

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I still think the squawker and tweeter are basically in parallel. I mean, you wanted to put 8 ohms across the tweeter as well, originally right?

I don't think tweeters impedance at 700hz is very relevant, as that first cap also sees the tweeters impedance at every frequency above 700hz as well, probably dipping down to 8 ohms or lower at some points, hopefully for an 8 ohm average at the tweeters normal operating range.... I know actual impedance is complex, but we use nominal impedances to calculate starting points for crossovers, don't we?

No, I still think the tweeters impedance in its normal operating range matters a good bit at that first cap.... I'll happily change my mind if you can set it out for me.....

I'm also beginning to think that a resistor isn't the way to go, for me. I calculated 180mw loss across the resistor at 1000mw input for my method, and my favorite amps only do 3500mw and 8000mw respectively. Now I'm trying to recalculate the first cap... I have some nifty vintage NYT/Westrex 1uf paper in oil caps lying around that would probably sound pretty good.....

All this is important, even from an experimenters standpoint, because you could fry a horn midrange by sending it too much bass, and raising the effective impedance seen by that first cap will lower the effective crossover point, yes?

It would be a bummer to fry a K-55-V....

Once again, I'll happily change my mind about anything if you can lay it out for me... I have no formal EE training, I do have experince in professional sound reinforcement (theatre and music) and building tube amps....

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Sorry to be a pest, John. Of course you are right. After doing the math a bunch of times, I finally figured it out.

Anyway, I tried this mod, and it works quite well, especialy if your Heresys are up on stands, away from the wall (like mine are).

Anyone who's thinking of trying something drastic (like swapping woofers) should try this first.

Now I'm going to pull the resistor, and try a 1uf NYT/Westrex PIO cap in place of the 2uf... I'll post results over in Odds and Mods....

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I'm glad you liked it!

Removing the resistor and changing the cap will work just as well, except for one thing. The midrange impedance will be about 250 ohms. I think that's too high for even SS amps.

Either mod should produce a generally flat frequency response curve, assuming the woofer doesn't have a big rise in output like many guitar speakers do.

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It sounds great, John! Suddenly, I can hear the Woofer.

I eventually removed the resistor and changed the first cap to a 1uf "NYT" (New York Telephone?) paper in oil cap. It had mounting ears just like the original. Easy peasy.

I would recomend this mod to anyone who has their Heresy's up on stands away from the walls, like I do.

Perhaps I'll fool around with changing the speaker taps to 16 ohms since the mid impedance is so high... but it does sound great just the way it is!

In case anyone is wondering my system includes:

Dual 505 Turntable w/Ortofon OM5e

Phillips CD Burner/Player

Dyna FM3

Modified Dyna PAS-3 Preamp (tone controls removed, boards recapped, and generally tweaked)

Homebrew Amps:

6B4G PP (approx. 8 watts)

6B4G SE (approx 3.5 watts)

(One or the other is always on my workbench)

Two homebrew sub cabs (15") driven by an Adcom GFA-1 through an old Heathkit(!) sub crossover

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  • 1 year later...

Hi John,

I just got my pair of Herey I last month from eBay. Did the mod suggested by Klipschguy in the other thread and there's certain extent of improvement. Will follow your ideas to move the mid tap to 01 and add the resistor next.

heresy01.jpg

heresy02.jpg

heresy03.jpg

Thanks for your suggestion!

3.gif

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  • 1 year later...

Al is correct. I wasn't thinking clearly. This was intended to be an easy mod and for a test, but the extra resistor should not be installed across the tweeter. I've uploaded a corrected version. We used to be able to delete files on the server. I can't figure out how, now.

So what is the final mod to the Heresy Type E crossover?

If I understand correctly, drop the squaker negative from the #2 tap to #1 and add a 16 ohm resistor across the squaker

and

Drop the Tweeter negative from the #3 tap to the #2 tap.

If I am replacing the caps anyway, can I just buy one 2 uF cap fo rthe tweeter and one 1 uf cap before the autoformer or will this create other problems?

Thanks,

Chris

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"So what is the final mod to the Heresy Type E crossover?

If I understand correctly, drop the squaker negative from the #2 tap to #1 and add a 16 ohm resistor across the squaker

and

Drop the Tweeter negative from the #3 tap to the #2 tap.

If I am replacing the caps anyway, can I just buy one 2 uF cap for the tweeter and one 1 uf cap before the autoformer or will this create other problems?"

You could do just that, but it will sound a bit smoother at the midrange crossover point if you use the 2µF cap with a 15~16 ohm resistor in parallel with the driver. The midrange horn causes impedance peaks at cut-off and a half octave above. The resistor swamps the impedance variations and the net result is smoother response.

Here is a typical horn and driver impedance plot:

http://www.jblpro.com/pages/pub/components/2426.pdf

With that big impedance peak around 500hz a 6dB crossover will have no attenuation there. With the parallel resistor it will. Impedance peaks of this magnitude cause peaks of distortion at the same frquencies on the order of 10dB or more.

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The midrange horn causes impedance peaks at cut-off and a half octave above. The resistor swamps the impedance variations and the net result is smoother response.

An area I've been struggling to understand. I get the impression the impedance issues are acoustic related, and are caused by reflections in the horn throat and mouth -- and it's difficult for me to grasp how adjustments in the filter squelch the peaks. On a practical level I understand the improvement swamping brings to the table because I can hear it, but I can't figure out how it works!

Something else I don't understand: I know the first order filters I like aren't first order acoustic filters. For example, what is a first order bandpass really doing if you have a horn/driver that has a natural 3rd order behavior in its rolloff -- which is basically what I see when looking at raw response plots of the Klipschorn bass bin and the K55/K401.

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Al is correct. I wasn't thinking clearly. This was intended to be an easy mod and for a test, but the extra resistor should not be installed across the tweeter. I've uploaded a corrected version. We used to be able to delete files on the server. I can't figure out how, now.

This is the first ime I actually seen the impedance values on a klipsch schematic for the autoformer. A lot of folks computed the impedance changes and disccused the effects those changes have on crossover frequencies due to user changes of tap settings.

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"I get the impression the impedance issues are acoustic related, and are caused by reflections in the horn throat and mouth -- and it's difficult for me to grasp how adjustments in the filter squelch the peaks."

They are caused by mouth reflections. Perhaps these figures will help:

http://forums.klipsch.com/idealbb/files/Olson%201.gif

http://forums.klipsch.com/idealbb/files/Olson%202.gif

You can tell how much the design cheats by looking at the magniture and spacing of the impedance peaks.

Adding the swamping resistor cannot alter the acoustic loading the driver sees (which causes the distortion to peak when the impedance peaks too), but it does allow the crossover to work much better.

About 30 years ago I built a very good sounding speaker with a 6dB crossover between the woofers and midrange driver. It sounded fine except for a peak in the response well below the crossover point. The impedance peak in the driver causes this. Adding a swamping resistor fixed the narrow, but annoying peak in the response.

If we use the JBL as a case in point, the impedance peak is close to 30 ohms or so because of the small mouth. All the Klipsch midrange horns are even worse in this department because they have even smaller mouths for their cut-off frequencies. The minimum impedance of the JBL looks like around 6 ohms or so, it is a nominal 8 ohm driver with a DCR of about 3,2 ohms

If you were to use a swamping resistor of about 10 ohms, the impedance peak will drop to about 7,5 ohms. The impedance minimum will drop to about 3,75 ohms. Attenuated 9dB through an autoformer will bring it down to about 101dB, good for a Cornwall type woofer, or a stacked pair of Heresy type woofers, and will present a nominal load of 30 ohms to the crossover.

A better fix would be to use an LCR network tuned to the impedance peaks. This requires some test equipment and a few more parts. See L3, L4, and L5 on the JBL K2 crossover:

http://manuals.harman.com/JBL/HOM/Technical%20Sheet/K2S9800-9800SE%20ts.pdf

"I know the first order filters I like aren't first order acoustic filters."

The transfer function is the sum of the acoustic response and the electrical response. A second order low pass combined with a third order high pass will give a 24dB/oct transfer function when used with a typical 6-1/2" woofer and a 1" dome tweeter when crossed around 2,5Khz. Horns are more complex, but the same principles apply.

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Attached is the last version of the Type E xover. I have all 3 of

mine wired this way. They are much closer to the tone of my La

Scalas. I have discovered that a 2 uF tweeter cap will give

a smoother response curve, so, I'd recommend keeping the tweeter cap at

2 uF.

post-2142-13819304346714_thumb.jpg

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Mark Kaufman said they were working on a kit so

that we could upgrade our Heresy's to that of the Heresy III. Why not

try the update?

No reason not to try it. I'd like to hear an HIII first and know a bit about the changes.

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Mark Kaufman said they were working on a kit so that we could upgrade our Heresy's to that of the Heresy III. Why not try the update?

I'll be looking forward to seeing that. It should be quite interesting.

There is an upgrade kit available for LaScala and Khorns and it is fairly pricey, but included the AK-4 crossover. It leaves the woofer in tact, since there is no change there.

OTOH, I think every element in the HIII is changed from the HI and HII. I would think the kit would include everything except the cabinet shell.

Parting out one's old parts on Ebay would be a significant help to defray the cost, though. Heritage parts often bring more piecemeal than selling the whole speaker as a unit.

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  • 1 year later...

bump.

I got around to doing the simple version(just changing taps and adding a resistor) last night and it sounds great.

I think it's a lot easier for my ears to pick up on some detail in the lower midrange and bass that I just wasn't noticing before because the squawker and tweeter were so loud.

I also realised that I had never gotten around to damping the squawker on the left side so I broke out the sculpey modeling clay and had at it(the sculpey in the right channel was still pliable after 5 years so I figured it should be good for another few.

Ahh,

I'm listening to music now.

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