Editorrr Posted September 28, 2014 Share Posted September 28, 2014 Hello!I really need your help. Please give graph impedance Klipsch Forte II. Thanks!!! Mikhail, Ukraine Quote Link to comment Share on other sites More sharing options...
beeker Posted September 28, 2014 Share Posted September 28, 2014 nominal impedance = 8 ohms Quote Link to comment Share on other sites More sharing options...
WMcD Posted September 29, 2014 Share Posted September 29, 2014 (edited) Hello! I really need your help. Please give graph impedance Klipsch Forte II. Thanks!!! Mikhail, Ukraine Good to hear from you Mikhail. I know your land is troubled. I had measured and posted the impedance of my Quartet some years ago. It is the little brother to the Forte II, with the Chorus II being the big brother. I think there is not going to be a big difference. https://community.klipsch.com/index.php?/topic/92689-best-speaker-tap-to-use-on-a-mcintosh-with-quartets/?hl=%2Bquartet+%2Bimpedance#entry1010458 Please read my notes on the print-out. Of course the actual data shows just how inaccurate the nominal impedance figure of one number for any speaker really is. I have Forte II at the office and listen to the world's best classical music station all day while I'm chained to a computer with MS Word. WFMT streams, so if you like classical, give it a try. If things go right, I'll drag the test equipment to the office next weekend, run some tests, and post the results here. It will be part of my labors to catch up with old projects which need doing. WMcD Edited September 29, 2014 by William F. Gil McDermott 1 Quote Link to comment Share on other sites More sharing options...
Editorrr Posted September 29, 2014 Author Share Posted September 29, 2014 Good to hear from you Mikhail. I know your land is troubled. I had measured and posted the impedance of my Quartet some years ago. It is the little brother to the Forte II, with the Chorus II being the big brother. I think there is not going to be a big difference. https://community.kl...ce#entry1010458 Please read my notes on the print-out. Of course the actual data shows just how inaccurate the nominal impedance figure of one number for any speaker really is. I have Forte II at the office and listen to the world's best classical music station all day while I'm chained to a computer with MS Word. WFMT streams, so if you like classical, give it a try. If things go right, I'll drag the test equipment to the office next weekend, run some tests, and post the results here. It will be part of my labors to catch up with old projects which need doing. WMcD I will be very grateful to you! I certainly need to know the impedance of Forte III have no way to measure yourself.In Ukraine, all will be well! We will win, because it is very much want to. Quote Link to comment Share on other sites More sharing options...
WMcD Posted October 6, 2014 Share Posted October 6, 2014 Please let me have a another few days on this. My test equipment uses a serial port. Two old laptops with serial ports, which I've used in the past, have failed. I'm off to Microcenter tonight to buy a serial to UBS adaptor -- which might solve the problem. WMcD Quote Link to comment Share on other sites More sharing options...
Editorrr Posted October 6, 2014 Author Share Posted October 6, 2014 Thank you very much for your help! Of course, I'll wait as necessary. Quote Link to comment Share on other sites More sharing options...
WMcD Posted October 7, 2014 Share Posted October 7, 2014 The result is attached as a .pdf. Impedance of Forte II.pdf 4 Quote Link to comment Share on other sites More sharing options...
Editorrr Posted October 7, 2014 Author Share Posted October 7, 2014 Thank you very much !!! Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted October 7, 2014 Share Posted October 7, 2014 That's no where near as bad as an RF-7. Quote Link to comment Share on other sites More sharing options...
WMcD Posted October 7, 2014 Share Posted October 7, 2014 So what does an RF-7 look like? WMcD Quote Link to comment Share on other sites More sharing options...
WMcD Posted October 8, 2014 Share Posted October 8, 2014 (edited) It is interesting to read again the analysis of the Cornwall by Mitja Borko. His work is the only comprehensive one of which I'm aware. He is probably calling it the Cornwall II because that is what Klipsch called when it first came into production. You can find a review on line here Other CW's before had the off center placement of mid and tweeter which led to debate over vertical or horizontal orientation. And early ones had the long slot for bass port. But he is talking about what we know as the CW. There was a later design called the CW II with plastic horns, of course. I post this because his analysis shows the electrical impedance which has a graph of similar shape to that of the Forte II which I measured and posted above. One of his comments is in error, IMHO. He seems to think that the resonance of the box and port is indicated by a sharp low frequency peak. That is not correct. It is actually the valley between the two peaks which indicates the box and port resonance and the resulting acoustic loading of the active bass driver. In the Forte II the dip is caused by the passive radiator and its suspension plus box "spring" rather than a port. But pretty much the same idea. There is a Dope From Hope about amplifier distortion which shows the electrical impedance of a Heresy. That is a box without a port. We see a hump in electrical impedance where box and driver diaphragm resonate, if mildly, with no port loading, in a sealed box. Conceptually, the electrical impedance just shows a mountain hump of a sealed box. If you have the port or passive, they make a valley in the middle. Otherwise . . . we see an increase in impedance in the midrange as the electrical loading of the midrange driver comes on. In the CW and Forte and the Heresy it is high up to the range of 50 to 100 ohms. This is the action of the autotransformer. Then it dips down again because the tweeter. Am I being too pedantic? An important concept is that we can look at the electrical impedance at the input and infer a good deal about what is going on with the electrical mechanical, and accustical items in the box. WMcD Cornwall Test Report.pdf Edited October 8, 2014 by William F. Gil McDermott 1 Quote Link to comment Share on other sites More sharing options...
WMcD Posted October 8, 2014 Share Posted October 8, 2014 Since I mentioned it, here is the impedance of a Heresy from a DfH. The tweeter is fed by the autotransformer but gets less voltage reduction than the midrange. This is to say the autotransformer is increasing the impedance for the tweeter but not as much as the midrange. This is why there is a big rise in electrical impedance in the midrange, range. Then (going up in freq) the impedance for the tweeter range is still high but not as high. As mentioned, there is a hump for the bass diaphragm resonance. WMcD 1 Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted October 8, 2014 Share Posted October 8, 2014 So what does an RF-7 look like? I don't have the graphs but it has a couple dips below 3 Ohms if I recall correctly. Quote Link to comment Share on other sites More sharing options...
Editorrr Posted October 8, 2014 Author Share Posted October 8, 2014 The result is attached as a .pdf. I concluded: transformer under pentode is best done at 6 ohms? (Excuse my poor knowledge of English ...) Quote Link to comment Share on other sites More sharing options...
Ski Bum Posted October 8, 2014 Share Posted October 8, 2014 (edited) My opt's only have 6 ohm taps, output impedance high at ~3 ohms, yet results in flat response from the mids/tweets. That's close to worse case scenario, not sure if your amp is quite as bad as mine. I wouldn't sweat it too much. Edited October 8, 2014 by Ski Bum Quote Link to comment Share on other sites More sharing options...
Editorrr Posted October 8, 2014 Author Share Posted October 8, 2014 My amp so far only in the project Quote Link to comment Share on other sites More sharing options...
Editorrr Posted October 8, 2014 Author Share Posted October 8, 2014 Quote Link to comment Share on other sites More sharing options...
WMcD Posted October 8, 2014 Share Posted October 8, 2014 The 6 ohm tap is probably good, unless you have a 4 ohm tap. Smile. WMcD Quote Link to comment Share on other sites More sharing options...
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