Al Klappenberger Posted February 1, 2006 Author Share Posted February 1, 2006 Guys, Here is three different analysis runs on the lowpass (woofer) filter of my ES400T extreme-slope Khorn crossover network. The three runs assume inductor Q equal to 5, 20 and 100. A Q of 5 is poor and a q if 100 is not atainable. The real-world Q of the inductors I am using is 20. I have assumed the capacitor Q is equal to 2000 in all three plots. Down that low a good capacitor will be virtualy lossless compared to the inductors. Notice how much greater effect the loss increase is as you approach the crossover. Also, note the actual relitive loss at the 400 Hz crossover itself. This is the attenuation at the marker in all three plots (400 Hz). This particular filter is actually optimized to compensate for the Q by designing in a peak at about 370 Hz. Bad Q casues the passband to "sag" as you get close to the crossover. All filter act this way. To make the statement that distributing the loss through the filter ranter than in an L-Pad following a lo-loss filter totally ignores this effect.Al K. Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted February 1, 2006 Author Share Posted February 1, 2006 Chris, A transformer attenuates by reducing the voltage applied to a driver by the ratio of the total number of turns in the winding to the number of turns the driver is connect across. This is called the turns ratio. A driver is a linear electric motor with a permanent magnet. If you move the diaphragm it will actually generate a voltage. It is actually a dynamic microphone. When a signal is applied to move the diaphrgm that same votage is generated. It is opposite the voltage that drove it to move in the first place. It is called "Back EMF". If the driver is driven from a high impedance, the driver will continue to vibrate when the driving voltage is removed. If a short circuit is applied at the instant the driving voltage is removed the diaphragn will stop vibrating much more quickly. To illustrate this, take any old loudspeaker you pulled out of a TV set and thump on the cone. Then short the terminals with a clip lead or wire and thump it again. The difference in the sound of the thump will be very noticable. An amp has a low source impedance and provides this short circuit when the driving signal is removed. This is called "damping factyor".If you stick an L-pad in the line the back EMF has to go through the pad to get to the short (the amp). It is now a relitive high resistance rather than a short. That louses up the amps damping factor. With a transformer there is no DC resistance. More importantly, the transformer now actually provides an even harder short becasue the back emf is step UP as it travels back to the amp. Remeber that a transformer will step down with a turns ration of 1/0.5 and Up with a ratio of 0.5/1. FOrward going energy is steped down but back emf is steped up. A lossey filter is like an L-pad. It's loss also is in the way of the amps damping factor. Therefore, a low loss filter and a transformer provides far better damping than a lossy filter having the same total loss. Al K. Quote Link to comment Share on other sites More sharing options...
mark1101 Posted February 1, 2006 Share Posted February 1, 2006 I see how the extreme slope is attained. Nice. Quote Link to comment Share on other sites More sharing options...
popbumper Posted February 1, 2006 Share Posted February 1, 2006 Thanks Al, that is much clearer. I was told that the autoformer was nothing more than a "long piece of wire" with several taps, but I felt all along indeed it was a transformer as described with specific turns ratios from which to choose and get corresponding attenuation. Thanks for clarifying this, and how it differs from a simple resistor. Chris Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted February 1, 2006 Author Share Posted February 1, 2006 Mark1101, "I see how the extreme slope is attained."Well, I really don't see how you can tell from the previous plots! Here's is the same lowpass showing the stopband area. That is, the frequency range that goes to the squawker. This really does illustate how the slopes are sharpened. Noice the way the low Q destroys the depth of the notch at 500 Hz. The assumed QL is again 100, 20 and 5. Also notice how the slope goes to pot and the crossover loss goes up MUCH more than the loss down at 20 Hz. Again, bad inductor Q does a lot more than just reduce the level to the driver!Al K. Quote Link to comment Share on other sites More sharing options...
Deang Posted February 1, 2006 Share Posted February 1, 2006 efzauner and Al -- you guys have had me in meltdown mode since last night. Egads. Nice lesson Al, I think it's finally sinking in. Truly humbling. Hi Chris. When you emailed me you said, "Have a question for you on the autoformers. I understand the concept, certainly this is a transformer with mutually inductive coils of different sizes allowing you to choose different dB attenuations. It occurs to me that one could choose a "single" coil pair to achieve the desired affect, since all the other windings are unused." My response was, "Nope -- it's just one long wound up wire! It's a single coil and the taps hang off different locations on the coil. The turns ratio determines the reduction in applied voltage and thus the attenuation level."If I wasn't clear I apologize. Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted February 1, 2006 Author Share Posted February 1, 2006 Dean, See... If you had palyed with that demo program I sent you, you would know all this stuff! [6]Al K. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted February 1, 2006 Share Posted February 1, 2006 Who, You ask how the different inductors will "sound". The answer is the same as how the different capacitor brands "sound". The answer is different for every person you ask and every speaker they go into and every room they are located in! You can't pin it down. Measured Q however is very easy to pin down. High Q makes a better filter and a better filter gives you a better network. What is a "better network", you ask. The answer again is who do you ask! The fact is that people hear what they want to hear. As only one person, my opinions count no more or less than anyone else. I restrict my comments only to what I can measure. This is called Science and can't be easily disputed. Al K. Al, wouldn't you say that the components that are MOST APT to be discerned as being "better" by MOST people under MOST conditions would be the ones that you would be most likely to select for your product? Granted that you would balance economy with performance, of course... Which end of the equation is weighted - "science" or "sale-ability"? DM Quote Link to comment Share on other sites More sharing options...
mark1101 Posted February 1, 2006 Share Posted February 1, 2006 Al, Thanks for taking the time to show evreyone this stuff. I barely follow now. I was sharper on this back in the school days. I don't know how much time you have but could you show a real life example like Solen Litz vs. copper foil at the cross over points for wooker and squawker bandpass? Your original chart shows closer Qs. My point is that the Qs were much closer than in these extreme examples. Show us how much better the Litz wire performs over the copper foils. As you probably know I had Super AA networks with the Litz inductors. I also have a pair of Super AAs with copper foils. Guess which ones sound better to me? Anyhow, I know your busy. Whatevre you have time to do. Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted February 1, 2006 Author Share Posted February 1, 2006 Dana, The choice of parts was done early on based on the experience I have had designing, and tuning L-C filters from audio to microwave since about 1973. I looked for the components that best met those specifications. Remember that all this began for me when I simply decided I didn't like the AA networks in my Belles. I redesigned them for my own use and put the design here on the forum for anyone who was interested to duplicate. I have fornd that everybody has their own unscientific opinion of what sounds good. A lot of them are totally laughable! Some are quite sensable. I offer what I consdier to be best and I back up my choices with science, not opinion. Not even MY opinion of what sounds best carries any weight, but the opinion of unbiased instruments. If I built every network with parts others thought were best I would be using stuff like Jensen paper in oil caps, stilts to space your speaker cables off the floor, ropes to hang the netwroks off the roof and all sorts stuff like that. I will use only parts that I believe are best and for reasons based in fact, not opinion. I offer this phylosophy for all those who appreceiate that type of approach. There are other options, like Bob's AA clones for example. I will never build Klipsch clone networks. If you want them, you know who will make them for you. If you want the type products I offer, here I am!Al K. Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted February 1, 2006 Author Share Posted February 1, 2006 Mark, It's very difficult to exactly simulate the response a given Q curve will have on a filter. As I explained before, how can you put the curves into the computer? It would require a that curve fit equation be made for each type of inductor that works properly over the entire frequency range being analyzed. That is not easy to do. I would have to actually expand the analysis program to input the curves in a standard format. That could be coefficients of a polynomial generated by a seperate cruve-fit program from Q data points. It would be very difficult to made universal and stable. If you have ever tried a high order polynomial fit outside its intened range you know they go off in strange directions very quickly. The best I can do is pick the Q on the curve at the frequency of the crossover, where it is most critical, I then assume that Q over then entire frequency range. The plots I posted are extreme just to illustrate what happens when Q changes. You can mentally interpolate between 100, 20 and 5 to see what effect different Q will have. the difference between 20 and 25 is not so dramatic compared to between 20 and 100. But going from soild wire to Litz wire is a major improvement. That's a factor of over 3:1 at 6 Khz Al K. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted February 1, 2006 Share Posted February 1, 2006 Al, I'm just trying to make a point for the edification of others. There is a point of diminishing returns, I think we all set that point based on other things than pure "science"... that's all. It has nothing to do with the quality of your work, which is unassailable in my book. DM Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted February 1, 2006 Author Share Posted February 1, 2006 Dana, "Al, I'm just trying to make a point for the edification of others. There is a point of diminishing returns, I think we all set that point based on other things than pure "science"... that's all." Absolutely. I try to account for the law of deminishing returns by ruling out extravigances like solid silver wire that cost megabucks for virtually no improvement. It's also why I use Solen FasCaps rather them other high priced caps. Cost is always a concern. Sure Hovland musicaps measure better, but they cost a mint when you are talking about values like 68 uF, or even as "small" as the 13 uF cap in the Klipsch AA. They provide a very tiny advantage compared to steping up from sold wire to Litz wire in the inductors. When you have no science to count on you would be picking the fancy foil inductor over the Litz inductor becasue it looks "cool" and it's a new and different concept and must be better. You will pay big bucks and it and it will sound fine, but a Litz inductor will sound just as good if not better when you put a blindfold on the listeners! PWK would really be having a good time flashing his little yellow BS button at most of this stuff. Another very appropriate quite by PWK is "Ho-Mum, another major break-through!". Believe me, it's like expecting a network to sound different after X hours of "break in"! It's only becasue you believe it and your mind is getting used to the new sound! I just can't accept that kind of input, even if it's from ME! I do NO TRUST MY ONE EARS! Even an improvement as major as the Tractrix horn. I had to send the Trachorn prototype to 3 different people I trust to get their opinion before I went forward with it. I had no way to measure anything but frequency response and intermod distortion, which I did first. Those two tests just don't cover it. It requires equipment I do not have to analyze acoustic propogation and reflect wave interferance and such! That is what is required. Al K. Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted February 1, 2006 Author Share Posted February 1, 2006 Guys, I would seriously like to run a Q curve on a 2.5 mHy foil inductor and compre it with the curve on the 2.4 mHy #14 soild wire inductors I use on my universal network. I believe foil inductors are not as good as Litz wire for tweeter filters, but I believe they deserve a chance to compete with solid wire for a woofer filter inductors. Does anybody have one of these laying around the might be willing to loan me for the test? I'm to poor to buy one just to test and throw out! Al K. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted February 1, 2006 Share Posted February 1, 2006 But remember that everyone has their own different point "of diminishing returns" to apply. I figure PWK had the same issues that we have today. Frankly some of his responses are way off base. But he was balancing the economics against the scientific, too. It would be natural to assume that PWK voiced his speakers by listening to them as well as using test gear on them. I assume a balance was acheived that way. Personally, I wouldn't want speakers that only get "tested" by machines. The human touch and discernment needs to be in there too. DM Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted February 1, 2006 Author Share Posted February 1, 2006 Dana, I KNOW PWK voiced his speakers by ear. I visited the Klipsch factory back in about 1976 or so. He had very crude test facility. There was no anechoic chamber. The equipment was all - hand crank type stuff! I think he only got better stuff later. The question is who's ear do you tuned the speaker by. Besides, I just do networks / filters! Al K. Quote Link to comment Share on other sites More sharing options...
popbumper Posted February 1, 2006 Share Posted February 1, 2006 Hi Dean: PLEASE know this was in NO way intended as a "question of your ability" or a slander, hence my not mentioning your name. The only reason I asked Al was because I found this thread interesting, and he brought up the "autoformer vs. L-pad" subject, and I thought it a good time to clarify. No slight whatsoever, I am glad we're all learning here and I really appreciate each of you - even with hot glue...;>). Chris Quote Link to comment Share on other sites More sharing options...
Deang Posted February 2, 2006 Share Posted February 2, 2006 I knew you didn't mean it like that, I wasn't upset at all. I am upset with Al though, because he knows I can't argue with math. I think it's cheating. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted February 2, 2006 Share Posted February 2, 2006 Dana, The question is who's ear do you tuned the speaker by. Al K. Ain't THAT the truth! DM Quote Link to comment Share on other sites More sharing options...
Deang Posted February 2, 2006 Share Posted February 2, 2006 Well, since he doesn't "trust his ears", we should probably use mine. Quote Link to comment Share on other sites More sharing options...
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