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About Langston

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  1. That is a fact. My stomach turned when I wrote that. Input and output power are almost equal with the autotransformer vs. a resistor L-Pad where power is dissipated to ground. And you're right - the swamping resistor is an expense - an expense I'm more than willing to pay given what I get out of it. Re: the Chief, I'd love to meet you - but I don't have the patience for fishing. Let me know if I'm a problem and I'll disappear. At this moment I'm half way through a Crosby Stills and Nash album using the Klipschorn as intended as a 3-way (triamplified), and cheating further with the Crites A-55-G/K-400 and DE120 Dave Harris Tractrix. Very nice, but falls short of the two 2-ways (biamplified) I've tried the last two weeks, even at low levels. At higher levels It can't flesh out the lower frequency meat that the 2 inch drivers deliver even though the crossover points are identical. L/R location is much more toward the loudspeakers, whereas the two 2 inch / Harris Tractrix 2-way setups I've tried result in the loudspeakers largely disappearing. Nevertheless I could easily live with this "classical" 3-way system. The ear/brain system adapts. "Helplessly Hoping" just started. Phenomenal. : ) God bless you and your precious family - Langston
  2. Sure enough, the battery on the (calibrated) Keysight U1733U was dead when I tried to use it for a second go at it. The new battery made the results quite different, which has been edited in the post. Apparently it has to source a fair amount of current to make larger inductance measurements. The Audio Precision measurements don't rely on batteries. : ) Thanks! - Langston
  3. Well, then, might as well finish by measuring the T2A a bit more. Universal Transformer knows what they're doing. Here's a screenshot of the tap to tap measurements of my pair of T2A's as well as the data from the LTSpice file that Mike gave us. There's a lot of difference between samples.. Or is there? : ) T2A L DCR.xlsx Since these things are basically L-Pads using inductors1, it isn't inter-tap absolute values that have to match, what has to match are the ratios between them because that's what causes the gain reduction. And these ratios match nicely. PWK did not compromise his life's work with the autotransformer. Small signal measurements of my pair of T2A's at each attenuation step with a 10Ω load in place of a driver. Now I take all (8) measurements and force the magnitude traces to intersect at 1kHz to see the overall variation between every setting of each AX. Phase is also shown, but it is not normalized. I've seen worse, but not from an autotransformer. : ) God bless you and your precious family - Langston 1 Nope, it ain't. An AX is a continuous winding on one core with one or more taps into those windings with its behavior determined by the ratio of turns or voltage or current, depending on how you want to measure it. I'm learning. : )
  4. Thanks Mike for the 3636 and T2A LTSpice component files. As you know LTSpice assumes ideal components, but also allows the addition of parallel and series L/C/R values to make the model act like the real thing. I measured a 3636 sample and got slightly different inductance and resistance values between taps than you did, but both models missed real measurements too much for my taste. I've attached my version of the 3636 component file that you can use to get my inter-tap values. Crites 3636.asc Still, the only reason to bother with such an exercise is if you don't use a swamping resistor on the input of the AX. With a 10Ω resistor across the AX inputs, the specific AX impedances become useless information because the resistor overwhelms everything downstream of it. The resistor is Borg - it assimilates everything - but in this case inductance becomes futile, not resistance! : ) So back to the real world that I know and trust - measurement. I decided to measure the voltage applied to the A-55-G driver input terminals simultaneously with the nearfield acoustic output from the K-400 horn (mic almost touching the grill cloth). Dean asked for the -3dB (0-4) attenuation setting, but I decided to use -6dB (0-3) to make transfer function defects, if any, more apparent. I don't include a series capacitor in this group of measurements because it would make things too busy. Next time. It doesn't reveal anything IMO. Conclusion: The 3636 is transparent at audio frequencies. All it does is reduce voltage like a volume control by the amount selected without messing with the time domain (phase, etc.). The max output of the 3636 decreases as attenuation increases, the specifics of which were shown here. Blue traces are the reference measurement without the 3636, i.e. with the amp directly connected to the driver. Pink traces add the 3636 set at -6dB between amp and driver without a swamping resistor. Again, each measurement includes two traces of the same color for the electrical input and acoustic output of the driver. Now what I've done is take those same traces and force each to intersect at a mid-point (I chose 900Hz). I also smoothed the curves to 24th octave. This makes it much easier to see if the frequency response varies when the 3636 is inserted in the circuit. Next is the identical plot except this time I include a third pair of (Green) traces that add a 10Ω swamping resistor on the input (0-5) of the 3636. Now the final nail in the coffin to dispel the AX phase error myth. Again, all three pairs of traces are shown. God bless you and your precious family - Langston
  5. Never! I'm only two weeks old with the Klipschorn. If Roy keeps the stunning bass slam of the Klipschorn while increasing LF extension with those ports, I'm going to rob a bank. Simple as that. Also, down here in the South it's considered bad manners to ask something like that without the possibility of a solution. Is there a pair setup somewhere in the US in a proper room where the room modes have been dealt with at the listening position? : ) Also: I haven't done the tuning for my 1 inch A-55-G/K-400 and DE120/Dave Harris Tractrix horn yet, so I haven't heard the Klipschorn as designed, well as a highly modified 3-way I should say. I never used the OEM woofers other than measuring their TS parameters (they're in good shape) - I installed the Crites cast frame woofers. Silly little 15 inch things with a tiny 150W rating (I'm used to pro audio) that almost knocked me on the floor. Those corner horns are brilliant. As of now I've only listened to the system as a two-way with Dave Harris' large wood Tractrix horn with the Faital Pro HF206 and B&C DE750. I also just got the B&C DCX464 with the big horn they made for it, but haven't even done the raw measurements on it yet. I assume that'll be the winner, but I've been wrong so many times. This is also taking longer than expected because everybody I know is coming over to hear the Klipschorns.
  6. You're absolutely right! The autotransformer would do just that and each tap would present yet a different inductance (one of the three parts of impedance) to the passive network that is loaded by the AX/driver combination. Thus different caps, etc., will have to be used due to the AX and changed again every time you choose different attenuation taps. Unless.. .. you use a swamping resistor and turn the AX/driver system into a resistor that barely changes value even as you change taps. Then who cares about the AX and driver with all their weird internal inductance/capacitance/resistance when all the passive network sees is what it thinks is a very close approximation to a constant value resistor? I wouldn't consider dealing with a moving target to load my passive network, thus it's AX plus swamping resistor or no AX for me. This plot illustrates what I'm saying - and please forgive me if I'm missing your point! And I'm still going to do those measurements you and Dean mentioned. : ) God bless you and your precious family - Langston
  7. Alright you whippersnapper, I re-ran the measurements again this morning, but only at the -9dB step on the 3636 so I could demonstrate a couple of other things. The measurement setup: APx515 output -> AHB2 (bridged, more power Scotty!) -> 3636 (0-5, 0-2 taps; -9dB) -> 10Ω 10W resistor across 0-2 output taps -> APx515 input. Notes: Adding a second 10Ω 10W resistor across 0-5 input taps slightly reduces distortion in the 3636 simply because it received slightly less voltage. The swamping resistor did increase distortion slightly in the amp due to the increased load. Thus I chose to skip the swamping resistor for all measurements until this post. The swamping resistor in parallel with the 3636's input also caused a slight increase in HF rolloff; immaterial in this application. I have (6) samples of the 3636, (2) made in 2016 (yellow tape), (4) made last month (white tape). They all measure virtually identically, thus I just used one installed in a jig for all measurements. The following Max Output plot was done entirely at the -9dB tap setting and adds measurements with the swamping resistor and 1dB into saturation (about 3% THD). Next zooms into the attenuation provided by the 3636 at each of the above drive levels and bandwidths. And a final effort to put a nail in the coffin of the autotransformer phase error myth. Options: 1. If you really want autotransformer behavior in your passive crossover and need more than 8dB attenuation, use a pair of inductors in an L-Pad type arrangement that can deliver the power you need to the driver without saturating. You loose adjustability but you retain the other benefits. 2. If you want to use the 3636 and need more than 8dB attenuation, use an active 2nd order (adjustable Q) shelving filter to reduce the passband further. There's another benefit to this in that near the crossover from low to mid/high, the shelving filter will also be pushing the nasty bass horn resonances further down. 3. Don't attenuate anything passively, skip passive impedance compensation, and don't use the passive network for any kind of EQ whatsoever. Design the passive network for proper high and low pass function alone, then use active filtering to do everything else. This will give you almost all the benefits of bi/triamplification while still being able to use a single (low output impedance) amplifier. Of course the loudspeaker will be useless without the active processing, like the new Jubilee. I stole this idea from the great Dave Gunness and used it extensively in concert production. Cut my amp racks approx. in half. 4. Be a sissy and use resistors. 5. Stop the insanity and go fully active, like the new Jubilee. Active will probably be cheaper by the time I'm done and may very well be what I end up with, but I wouldn't have learned anything. PS: I've been cheating the whole time I've been writing these posts and using fully active DSP bi/triamplification to design and tune my Klipschorns. Once I decide on the endgame for the top hat, I'm hoping for a passive solution with flat impedance around 6Ω from 40Hz to 20kHz. The Klipschorn is the most exciting loudspeaker system I've ever heard in my life. I always thought this was possible, but not until a couple of weeks ago did I experience it. God bless you and your precious family - Langston
  8. Spot on. I was wondering if someone would point this out. : ) 2.7W in dB is 10log(2.7) = 4.3dB that you add to the 110dB sensitivity for 114.3dB maximum peaks. That's loud, but for midrange peaks I'm aiming for at least 120dB. The orchestral stuff I like most hovers around 20dB or more crest factor (peak to RMS), which means I'm in the upper 90's (loud as heck) RMS. I go there sometimes. It's also a little rude to pony up for a pair of drivers like that and adjust their effective max. wattage rating down to 2.7W. : ) God bless you and your precious family - Langston
  9. Third measurement group: Transfer function analysis. (Addendum) We found out from my previous post's Max Output plot that both the 3636 and T2A have attenuation settings (taps) that shouldn't be there. The 3636's -9dB (5.4W) and -12dB (2.7W) taps are unusable due to the very low output available before clipping (saturation). The T2A's -12dB tap shares the same 2.7W clipping threshold. If I didn't err in my measurements, the 3636 is unusable from -9dB to -12dB and the T2A is unusable at -12dB. Because I'm so interested in using the 3636 in my passive crossover designs I went back and performed all the measurements again, and this time I measured each 1dB step of the 3636. Turns out my prior measurements were correct, but I want to spill the beans on what I learned. Somebody (Universal Transformer or the Crites or both) should have warned us about the 3636 limitation. I suppose it's very rare for anyone to use those things at greater than 8dB attenuation, but the additional taps really shouldn't be there. First, the good news. Each gain step is dead-on. The thick traces from 100Hz to 10kHz are the Max Output measurements. They overlap the low level, wideband measurements because the 3636 (and T2A) attenuations are constant regardless of drive level (within their linear regions). Next is the Max Output (watts into 10Ω) plot at each of the 12 attenuation steps. Finally, I made a cheat sheet for the 3636 that should be helpful. Red is bad. There's a download link for a PDF version below the picture. 3636 Autotransformer.pdf God bless you and your precious family - Langston
  10. Third measurement group: Transfer function analysis. Since I've already prepared the electrical domain measurements, I'm going to post them here and add a 4th post to cover questions. So far I have (2) from @mboxler and (1) from @Deang. Everyone is invited to fire away with more questions and I'll answer them (with measurements) if I'm able. One of the questions has to do with inductance values of the AX between the 0-3 output. A note on this: I've decided not to try to figure out how to accurately add the AX to my crossover optimization software, instead I include the swamping resistor plus AX in my driver impedance measurements as if the driver came with that stuff built inside of it. The 3636 AX does not change acoustic magnitude or phase measurements, it only applies attenuation, thus no need to include the AX. Thus I avoid screw ups characterizing the AX as a simple pair of inductors in L-Pad configuration, which I assume it is (nope, it's a continuous coil sharing the same core with taps). If someone has successfully modeled an AX in Spice type software such that the predictions proved correct, please let me know. : ) - - - I show two measurements of each AX; the 3636 and a '74 vintage T2A/3110A. The first is low-level, wide bandwidth and the second is the most the AX can handle at a given attenuation level between 100Hz and 10kHz. Even though the 3636 can do 1dB attenuation steps to -12dB, the T2A only has four output taps at -3dB, -6dB, -9dB and -12dB. Thus I decided to measure each AX at those attenuation levels. Every measurement included a 10Ω load resistor across the AX output to simulate a driver. First up is the reference measurement of the AHB2 amp in bridged mode into 10Ω alone. I only took it up to 200W because that was the max that either AX could handle. Next is phase and group delay (which is just another way to look at phase). I include every measurement made just to get it out of the way because both AX units were effectively perfect through the audio range. You'll see a small bump at the beginning of the high level 100Hz-10kHz sweeps. That's due to suddenly hitting the AX inputs with high power. If you happen to do that to your loudspeakers at some point, that little bump will be the least of your worries. Next is low level wide bandwidth output and THD. The dashed traces are the T2A, the solid traces are the 3636 (as on every plot). Next are the maximum outputs at each nominal attenuation setting that remain under 1% THD. I adjusted the generator in 1dB steps. Once the AX exceeded 1%, I dropped the generator level 1dB and recorded that as the max. This wattage level is across the output loaded by 10Ω. To figure out the much higher wattage absorbed by the 10Ω swamping resistor on the input, multiply the -3dB output by 2, -6dB by 4, -9dB by 8 and -12dB by 16! There is a surprise in this one. The T2A for the first time outperforms the 3636 at something. At the -9dB attenuation setting the T2A's max output is as expected, mid level between the -6dB and -12dB settings, but the 3636 is low. It must be a design issue (due to the 1dB steps?) because I got the same results with a 2nd unit that is 3 years newer in mfg. date. It's fine for our use, but it shouldn't do this and I'm going to look into it. Next are the actual attenuations provided at the four nominal level settings. This includes both low and max levels. The 3636 nails it, but the T2A is only off by 0.6dB worst case. God bless you and your precious family - Langston
  11. So turn off your air conditioning if you don't want to "waste" power. You'll live. Alone maybe, but you'll live. You buy comfort with that power usage, I'm gonna buy a resistive loudspeaker over the lion's share of its output for the sake of rock solid passive network behavior regardless of voice coil temps and the ability to use tube or constant current amps without having to measure the system and apply inverse EQ to it to flatten it back out AND the ability to change mid/high attenuation levels at will, and driving the system with a single amplifier. Cranky soldermeister indeed! : ) BTW, thanks for the suggestions for other measurements. I also genuinely enjoy and learn from your posts - it's hard to interpret weird people's writing like my own at times, thus I'm stating that for the record. : )
  12. So true. Dick Heyser was a huge fan of the Nyquist plot and I'm a huge fan of his, so I tried and tried to learn to love it, but me and the rest of the pro audio world pretty much let it die out with the TEF analyzer. Still, you can see stuff in it that isn't apparent with any other plot and if you work at it you can ignore many traditional plots and rely on the Nyquist. For example, the horizontal axis (real) is SPL (presented in pressure units above), the vertical axis (imaginary) is - wait for it! - the VELOCITY of the sound. That is so cool because sound only moves air particles back and forth, the speed of which increases with frequency. Thus, high frequencies move the air particles quicker, which takes more energy, thus when you are a good distance from a concert venue, only the low frequencies remain. The mass of the air molecules damped out all the highs. Sound PRESSURE on the other hand travels the distance from source to receiver. Just like a wave in the ocean that travels hundreds of miles, the actual water stays where it is - the water just bobs up and down as it passes - the distance between crest and trough is the loudness or SPL of the wave and the amount of time it takes is frequency. The Nyquist pressure is also a circular plot of the impulse response! And you can see magnitude and phase in there - but you have to think 90˚ (Hilbert transform-like). You can see all that stuff in the Nyquist and a heck of a lot more, BUT it's hard to apply much of it to the stuff we do. Thus the lack of interest. : ) God bless you and your precious family - Langston
  13. I have a pair of '86 vintage Heresy II's that still work perfectly in spite of the dried out looking woofers. They are a study on how much phase rotation we can put up with and still have amazingly good sound. Mine disappear under 90Hz or so, thus wall or corner placement can help a lot. I'm going to read that Super Heresy 1.0 thread. : ) This is an Excel based presentation of the Heresy II's transfer function back when I was playing around with Nyquist plots: God bless you and your precious family - Langston
  14. Second measurement group: The autotransformer's impedance effect. With passive crossovers and horns, significant mid/high frequency attenuation relative to the low frequency passband is required. My taste at present for the Klipschorn is about 7dB less mid/high output after equalizing for room acoustics under 200Hz or so. Before playing bop-a-mole with the room modes, I needed a 10-11dB mid/high reduction for balance but the bass quality remained unacceptable, of course. The two huge benefits of the AX over resistive pads are the ability to change mid/high attenuation without screwing up crossover response (when used with a swamping resistor), and immunity from voice coil temperature changes. Both benefits result from the AX's presentation of a constant impedance to the passive crossover network. This also allows simpler crossover design (imagine building a network for an 8Ω resistor) and the ability to use any genre of amplifier without tonal changes. Downsides? Phase? Group delay? Inductance? Distortion? Frequency response? That's coming up in the third measurement group. Very helpful post by @henry4841 on the AX background, thank you. I am a newbie at home audio and it's turning out to be as hard to get right as professional audio - maybe harder. I thought it might be boring at first and so far it's kicking my butt. Thanks also to @mboxler for the series capacitor idea - will do, but given that I'd lose most of the impedance compensation benefits without a swamping resistor, it too will be part of the setup. Without the swamping resistor the AX doesn't interest me. The first of several iterations to my '74 Klipschorn top hats used a Crites sourced DE120 high frequency driver with their horn and A-55-G mid frequency driver for the existing K-400 horn. The latter was a big improvement across the board, but the little horn provided with the DE120 resulted in a rough rolloff right around the crossover frequency, thus I got Dave Harris's (Fastlane Audio) drop-in wood Tractrix horn and the DE120 became nearly flat down to 1kHz with a rolloff that looked just like the B&C literature. Brilliant. The following impedance measurements use these two driver/horn combinations without any passive components other than the 3636 AX and a 10Ω swamping resistor across its input. Raw measurements of the DE120/Fastlane Tractrix and A-55-G/K-400: The A-55-G/K-400 adding the 3636 at -3dB and -5dB attenuations: The same, but this time with the magic swamping resistor: Finally, the DE120/Fastlane Tractrix and 3636 at -3dB with and without swamping resistor: God bless you and your precious family - Langston
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