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A circuit consists of a 4mH inductor in series with a 6 ohm resistor. A 100uf capacitor is across the resistor. Frequency is 170Hz. At that frequency, the impedance of the parallel resistor capacitor is 5.05 ohms @ -32.65 degrees, and the impedance of the inductor is 4.273 ohms @ +90 degrees. Add the two together and you get 4.525618 ohms @ +19.99 degrees for the entire circuit. 2.83 volts (amplifier) into 4.525618 ohms (circuit impedance) equals 0.62532896 amps. 0.62532896 amps into 5.05 ohms (capacitor/resistor impedance) equals 3.1579 volts. The voltage across the resistor is higher than the amplifier voltage. Danny would say the extra voltage comes from the capacitor(?). I think it's because the impedance of the capacitor/resistor (5.05) is greater than the impedance of the entire circuit (4.525618). Or are we both saying the same thing in a different way?

My take on this is more mathematical. I'll update this post with an example soon.

Danny Richie of GR Research says yes. He discusses this 7:20 into this video... https://www.youtube.com/watch?v=RrpIBQ7gW5Q I think the extra voltage comes from the amp, not from the shunt capacitor. Thoughts?

I decided to leave my Heresy E2 crossovers alone, so selling the JEM kit. $30 shipped. Mike

I measured Le on my Hersey K-22-R's (Rola, I believe), and got 2.2mH @ 1000hz 😮. I realize voice coils are not true inductors, but is it okay to measure them this way? Using a DER EE DE-5000 LCR meter.

Nice idea, but I decided to measure my other Khorn, and came up with this plot. Red is the left speaker, green the right. Way different up to 75hz. When my back recovers from shoveling the snow coming in later, I think I'll swap the two speakers and re-measure. This will tell me if it's the room or the speakers???

Well, measuring voltages is a lot easier than SPL 🙁. This is what I get measuring my Khorn bass bin only, no crossover. I assume the big suck out at 60hz is my room? 1/24 smoothing.

I agree with all your points. In my case, much of what I'm doing is educational. When I first started this "hobby", I knew nothing about crossovers. I then built ALK's Universal kit, and had no idea what the components were doing. The schematic called for a 1.3mh woofer inductor. Al's point was that the 1mh voice coil should be subtracted from the normal 2.5mh inductor used in, say, the Type AA. A couple of years ago I replaced the 1.3mh with a 2.5mh. I soon began to wonder what was really going on. Attached are plots of various lowpass filters (voltages are across a K-33-E in my Khorn). Blue is 1.3mh Green is 2.5mH Black is AK-3 Red is AK-4 (I only have a 5.4mH inductor, so I used 200uf to arrive at the same resonance frequency) Next step is to measure SPL using these filters.

Apologies to the OP, but Dean made me do it! I realize I don't have the most sophisticated equipment, but here are my findings. This is the transfer function of a 4.1mh inductor with a 6 ohm resistor load. A capacitor is across the resistor to create a 2nd order filter. The blue plot is a 33uf electrolytic that measure 29.9uf and .44 ohm ESR. The red plot is a 30uf Solen polypropylene (I don't have a polyester) that measures 30.25uf and .01 ohm ESR. It's hard to see, but the max difference is around .3db. Not sure how audible this would be.

Thanks for the links! My searches didn't help much.

I realize I'm one of very few that finds this interesting, but at least I have a handy way of documenting my results. Apologies to all that view this, only to immediately press the back button. My experiments have revealed some interesting things (to me anyway) regarding low pass filters, in my case, to a K-33-E installed in my Khorns. I never realized how much the voice coil influences a passive crossover. On the attached plot, the yellow represents the voltage across the K33 in series with a 2.5mh inductor. Notice how the voltage starts to drop very early and continues to drop, eventually at a 3db per octave rate. I've never used a zobel network, and decided to give it a try. I settled on a 4 ohm resistor in series with an 80uf capacitor, in parallel with the K-33. Since this gives me a pretty constant impedance of around 4 ohms from 200hz on up, I chose a 1.6mh inductor for the next test. A 1.6mh inductor is around 4 ohms at 400hz. The purple represents the K33 voltage. As you can see, it looks more like a first order low pass at 400hz. I'm curious why zobels aren't used more often. With one, it's easier to shape the woofer voltage knowing that the voice coil inductance isn't messing with the frequency response of the crossover.

Just in case that document doesn't address your question directly... An autoformer has no polarity. The taps on the 3619 are 5, 4, 3, 2, 1, X, and 0. If you connect input + to tap 5, and input - to tap 0, then tap 4 will be + and tap X will be -. In fact, given that input configuration, the output tap closest to tap 5 will be +, and the output tap closest to tap 0 will be -. Now, if you were to connect tap 4 to the driver - and tap X to the driver +, the polarity to the driver will be reversed. Al does this with his Universal to help correct the phase shift created by the 2nd order low pass ahead of the autoformer.

I believe that's how Al simulates the K-25-K woofer. Don't include those components.

According to this old thread, the early AL crossovers did not have zener diodes. https://community.klipsch.com/index.php?/topic/73232-schematic-for-type-al-crossoveranyone/

I'm sure your back will object, but if it were me, I would rule out as much as possible before doing anything. I am curious, though. When you say "volume at 80" is that 80 out of 100 or -80db?

How did this test go?

Even this doesn't seem correct to me. Isn't the Forte II K-25 woofer 4 ohms? I just read another post that said the DC resistance at the speaker terminals measured 4.3 ohms, which sounds right if you add in the DC resistance of the inductor. He also noted that the impedance of the speaker drops below 4 ohms between 100 and 200hz. That's a lot of current! Might be interesting to remove the wires from the woofer and measure the DC resistance across the K-25 terminals.

I would describe it more as scuffed or untidy. Can you take a picture from the other side? Perhaps the 110uf electrolytic capacitor has failed, but we can guide you through some further measurements.

Even though I'm not a Sonos user, I still found this kinda cool. Each Symfonisk contains multiple chips, including a PCM5102A DAC and TPA3116D2 class D amp. All set up to stream, bi-amp, and apply room correction for the two internal drivers. This gentleman bypasses the internal Symfonisk drivers and connects the amps directly to the KG4 drivers. Around 14 minutes. https://www.youtube.com/watch?v=-8iCWKtsq8U

Nice! I assume you can also measure voltage across crossover outputs? I'm going to build a new crossover for my Heresy's, but was curious what the current E2 crossover was doing. I'm using REW to do the sweep/measure, and this is what I got. Would be nice to have one of those devices to verify my results. Red amp, upper green woofer, blue squawker, lower green tweeter.

It's a stereo version though... https://www.ebay.com/itm/313680365069?hash=item4908ce860d:g:APsAAOSw-QthR2CA

Hey Jon The best way would be with a true rms multimeter. I'd actually measure a few things... Play a test tone, say 1000hz. It doesn't have to be real loud, as you are just creating a voltage that can be measured. Measure the voltage across taps 0-5 of the T7A autofomer (input). Measure the voltage across taps 0-2 of the T7A autoformer (output). This should measure around .316 times the voltage across taps 0-5, or -10db. Measure the voltage across the wires connected to the squawker. The difference between this voltage and the voltage across taps 0-2 is the attenuation created by the lpad. If you are curious about the difference in db, you can enter the measurements here... http://www.sengpielaudio.com/calculator-amplification.htm I hope this is what you are after. Mike

Stumbled across an old thread where Bob Crites posted several autoformer PDF's. The T4A was one of them, so I now know the specs. https://community.klipsch.com/index.php?/topic/87280-heresy-ii-crossover-schematic-cleaned-up/

I thought I'd use this technique to see what, if any, effect the inductance of an autoformer (in this case a T2A) had on the frequency response. I ran two measurements. First (red) was a 27.2uh capacitor in series with a 14.62 ohm resistor. The second (green) was a 6.8uf capacitor connected to tap 5 of a T2A. I then connected tap 3 to the same resistor. Since the load on the capacitor now 4 times the resistor, I used a 27.2 / 4 capacitor. I then added 6db to the green plot. As I thought, the inductance between taps 0 and 3 of the T2A does contribute to the frequency response. Trying to figure out how to run this same test on a K-55M/K-400 to get a real world plot. Mike

Oct 1989: The AK-3 network was introduced to correct for a shift in the output of the K-55-M mid-range driver. I assume that meant phase shift, but maybe not??? It's only 1 db higher, but the woofer capacitor and squawker inductor were changed as well.