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What provides inductive element in mid crossover with autoformer?


efzauner

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Most klipsch crossovers use an autoformer to reduce mid (and sometimes HF) level.  But what provides the inductance for   mid upper frequency cutoff? None of the posts seems to cover this. My KLF20, and most other heritage do not have a mid inductor in parallel with the mid driver. The KLF30 does.  Is it the natural horn rolloff?   Would modifying my KLF 20 crossover to be closer to the KLF30 (while adjusting autoformer taps) make much of a difference? 

 

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The simple answer is: voice coil inductance.  But this has nothing to do with the autotransformer.

 

Don Keele (my favorite) tells the story: 

 

http://xlrtechs.com/dbkeele.com/PDF/Keele (1977-05 AES Preprint) - LF Horn Design Using TS Paras.pdf

 

PWK had a thing for using the minimal number of components in crossovers.  

 

I don't know about your KLFs

 

WMcD

 

 

 

 

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13 hours ago, efzauner said:

Most klipsch crossovers use an autoformer to reduce mid (and sometimes HF) level.  But what provides the inductance for   mid upper frequency cutoff? None of the posts seems to cover this. My KLF20, and most other heritage do not have a mid inductor in parallel with the mid driver. The KLF30 does.  Is it the natural horn rolloff?   Would modifying my KLF 20 crossover to be closer to the KLF30 (while adjusting autoformer taps) make much of a difference? 

 

I think you are misinterpreting the crossovers and the function of what is done by the components.

I believe the coil in the klf30 is used to increase the slope of the crossover for the high pass, not the low pass.  

 

When inductors are used for low pass, they are usually in series with the driver to provide a shunt vs. parallel.

 

Klipsch often uses the natural rolloff of the driver as the crossover point and low pass.  As WMcD stated above, minimal number of components to reduce loses of those components.

 

To establish a target frequency with a steeper rolloff would require changing the capacitor.

 

 

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1 hour ago, pzannucci said:

I think you are misinterpreting the crossovers and the function of what is done by the components.

I believe the coil in the klf30 is used to increase the slope of the crossover for the high pass, not the low pass.  

 

When inductors are used for low pass, they are usually in series with the driver to provide a shunt vs. parallel.

 

Klipsch often uses the natural rolloff of the driver as the crossover point and low pass.  As WMcD stated above, minimal number of components to reduce loses of those components.

 

To establish a target frequency with a steeper rolloff would require changing the capacitor.

 

 

yeah thanks PZ,  my bad, it was late. I should know this.  The Series VC inductance will be open at HF and regulate the upper LP, with the cap setting the lower frequency HP..  What is odd is that the KLF30 xover is at 825 while the KLF20 is at 750.  One would expect the KLF20 needs a steeper lower cutoff.   The big 12 inch woofers must be able to go higher than the 10s or are they trying to hide some roughness of the mid between 750 and 825?  Everyone says the KLF30s are a cut above the 20s   maybe this is why.   Both have the same power handling so the extra inductor of the 30s are not there for increased power handling... Still trying to fix my KLF20s, took them apart again. the xovers look fine. May get Crites autoformer and add a terminal block/solder wires to drivers.etc. 

 

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6 minutes ago, efzauner said:

yeah thanks PZ,  my bad, it was late. I should know this.  The Series VC inductance will be open at HF and regulate the upper LP, with the cap setting the lower frequency HP..  What is odd is that the KLF30 xover is at 825 while the KLF20 is at 750.  One would expect the KLF20 needs a steeper lower cutoff.   The big 12 inch woofers must be able to go higher than the 10s or are they trying to hide some roughness of the mid between 750 and 825?  Everyone says the KLF30s are a cut above the 20s   maybe this is why.   Both have the same power handling so the extra inductor of the 30s are not there for increased power handling... Still trying to fix my KLF20s, took them apart again. the xovers look fine. May get Crites autoformer and add a terminal block/solder wires to drivers.etc. 

 

I've often thought the same things as you.  I would have expected the 30 to be crossed lower than the 20 made more sense but not the case according to Klipsch.

The steeper crossover could actually be for power handling since those numbers are likely very rough.  The 30's likely intent would be for louder usage (along with higher efficiency) that the 20's aren't typically going to see.

I have dual klf-20 woofers in my hand built speakers and even in a wide open area attached to a 23x24x9 room, can crank shaking the foundation so not sure how much more you would want though the 30s can do more.

I will say that if the 30's had a mid bass, they would be an extraodinary speaker as the twelves can sound a little tubby in the midbass-crossover region.  Dropping the mid to 700-750 with tweaks to the crossover might resolve that.  Something the 20s I have heard don't have.

 

If you did go for a steeper slope on the mids and woofer, that might tighten up the imaging some due to lowering the driver overlap.

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ok so why does this autoformer T2A have inductance specs? Do these not play a role at all? I would expect the autoformer to have a Thevenin circuit of voltage source  with series resistance and the inductance of the coil. .... have to research this more... tranformer equivalent circuits and  inductance...leakage inductance etc. 

T2A.jpg

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I had tested this before, thought I'd try again.  I find this stuff fun, but I'm weird.  

 

I applied a 5.05 volt, 1160 hz signal to a dummy crossover (yes, I named it after myself).

I picked this frequency because at 1160 hz, the impedance of the 6.66 uf capacitor I used = 20.6 ohms,

and the impedance of the 10.3 ohm resistor I had across taps 0-4 should double.  This would be the 

resonance frequency, the frequency at which the voltage across the load (taps 0-5) should be down 3 dB.

 

6.66 uf cap between input positive and tap 5 of autoformer.

Wire between input negative and tap 0 of autoformer.

Wire between tap 0 of autoformer and one end of 10.3 ohm resistor.

Wire between tap 4 of autoformer and the other end of the 10.3 ohm resistor.

Input voltage, 5.05 volts at 1160 hz

Voltage across cap, 3.61 volts

Voltage across taps 0 - 5, 3.66 volts

Voltage across taps 0 - 4, 2.58 volts 

 

Now the fun part.  The impedance of a 6.66 uf cap in series with a 20.6 ohm load is 29.135 ohms.

                                  The current of 5.05 volts thru a 29.135 ohm load is .17334 amps.

                                   .17334 amps thru a 20.6 ohm load (the capacitor) = 3.57 volts...pretty close to the 3.61 I measured.

                                   Voltage across taps 0-4 should be 3.61 * .707, or 2.55 volts...again, pretty close to the 2.58 I measured.

                                   

This confirms to me that the autoformer (at least when using it to attenuate the K-55 by 3 dB),  doesn't have much if any affect.

 

Mike
 

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 The 30's likely intent would be for louder usage (along with higher efficiency) that the 20's aren't typically going to see.
I have dual klf-20 woofers in my hand built speakers and even in a wide open area attached to a 23x24x9 room, can crank shaking the foundation so not sure how much more you would want though the 30s can do more.
I will say that if the 30's had a mid bass, they would be an extraodinary speaker as the twelves can sound a little tubby in the midbass-crossover region.  Dropping the mid to 700-750 with tweaks to the crossover might resolve that.  Something the 20s I have heard don't have.
 


When I had 20's in here side by side with 30's the 20's had a slightly sweeter, tighter punchier bass. Same kind of sound but significantly 'smaller' compared to the 30's sound. I really wish I had never let them go.

The 30's seem to come into their own at louder volumes. Their bass can be somewhat fuller and relaxed at lower volumes which I can kinda see how someone could describe it as tubby compared to 20's but it's really not. North of 85-90db and especially north of 100db is where they really tighten up and impress.

The 20's just might be more compatible in a modest sized listening room. It has occurred to me that these KLF's might just be the ultimate DIY speaker. Spending a few bucks on them.....put a few bucks back into them and you've got a real good performer for a fraction of the cost if bought brand new.



Sent from my SM-G950U using Tapatalk

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