colterphoto1 Posted August 11, 2015 Share Posted August 11, 2015 My 77 Khorns have one tweeter that is significantly weaker than the other. They have BEC AA networks so I don't think there is an imbalance there. The diaphragms are not blown as they create sound properly, just one is less output than the other. So much so that I can't listen to them without going slightly crazy. These are the round back Alnico tweeters btw. Here's what I propose to do about it. Gather up 5-6 K77's on my work bench. Fire them each up individually using an AA network, using pink noise and phone RTA, also music and my ears To determine the best matched set, then reinstall them in the Khorns. Any issues with this methodology? Failing this, I might just spring for new K77F's, I think the AK5(?) total rebuild kits are out of my price range for now. M 1 Quote Link to comment Share on other sites More sharing options...
mark1101 Posted August 11, 2015 Share Posted August 11, 2015 Mike, I had the same issue. It's a known issue with the old Alnicos. Nothing wrong with what you are doing. It would be worth it to ask Bob C. if changing the diaphragms would help. I can't remember what he did to balance mine out. It might have been sending me a replacement that was closer to my good one. But I do think he may have ended up changing a diaphragm. Quote Link to comment Share on other sites More sharing options...
jimjimbo Posted August 11, 2015 Share Posted August 11, 2015 Michael, I think your test method is just fine. I have a couple of the same tweeters that I should test as well. What are you using for generating the pink noise? Quote Link to comment Share on other sites More sharing options...
karlson3 Posted August 11, 2015 Share Posted August 11, 2015 (edited) good idea - - you could test just the tweeters as I did with these 10 Goldwood KSN1005 knockoffs to see their response. Use say a 2uF cap highpass at low drive level or resistively load the woofer and mid sections of your AA network Edited August 11, 2015 by karlson3 Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted August 11, 2015 Author Share Posted August 11, 2015 (edited) I have a pink noise generator as part of my RTA iPhone app, but also a CD and a copy of that track on my iPod that I frequently use for PA applications (iPod playing through PA, iPhone in my hand watching the chart as I walk the room/grounds). Have a couple old MCM (like Parts Express) EV35 (M type) tweeters in a Hersey box that I could steal and get away from the alnicos. Have a set of BEC early 4500 design networks and his tweeters that I could then retrofit back into the Heresy box. That makes everything whole again without buying a single part. While I'm at it, I have two solder lug K55V in a drawer that I replaced diaphragms in 2009 (I think they came out of my MCM1900's) that I could swap into the Khorns as well. What's in there now is the push pin type and BEC A/AA does NOT have the P-trap circuit to get rid of the 9k spike. M Edited August 13, 2015 by colterphoto1 1 Quote Link to comment Share on other sites More sharing options...
Bacek Posted August 11, 2015 Share Posted August 11, 2015 Push-pull version has 9k spike not 6k spike. 1 Quote Link to comment Share on other sites More sharing options...
Schu Posted August 11, 2015 Share Posted August 11, 2015 (edited) Isn't it a given that they will all be slightly different? Maybe it shouldn't be "matched pairs", but "CLOSELY matched pairs"??? Edited August 11, 2015 by Schu 2 Quote Link to comment Share on other sites More sharing options...
garyrc Posted August 11, 2015 Share Posted August 11, 2015 (edited) A pair of 1970s T-35 (~~ = K77) roundbacks we have on the TV system in the bedroom are very different from one another. While it is true that EV never advertised them as "matched," they are so, so different!! Good News: The K 77 Fs (flat back, of course) in our main system, when Audyssey XT EQ'd are almost exactly equal (1/3 octave smoothing, because that's what I thought matched human hearing at the time -- now, reading has sown doubt) above the 4.5 K crossover on up to 16K, as measured using REW from the main listening position (didn't measure them with Audyssey turned off, because the system sounded so much better with Audyssey). There is a little ripple of difference @ 5 to about 6.5 K, but otherwise the overlay graph was just about perfect. The mid frequencies are not that equal (although good), and the bass is rather different, even after Audyssey. Bad News: The two K77 Fs sound different, no matter which ear is toward them, and no matter whether I'm facing the Khorns on the front wall, or facing the rear of the room. Edited August 11, 2015 by garyrc Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted August 13, 2015 Author Share Posted August 13, 2015 Gary, would be interested in your outcome of RTA without the Audyssey, as a true test of the similarity of the K77F. How is such a simple device so far off, even a pair of modern ones? 2 Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted August 13, 2015 Author Share Posted August 13, 2015 Push-pull version has 9k spike not 6k spike. Edited, yeah I was wondering about the number as I was typing that. Thanks for the correction. Sometimes I wonder if I'm hearing things, but the longer I'm in sound reinforcement the more I"m sure that I can trust my ears. Sadly that means I hear every little nuance and aggravating sound as well. Recently pointed to a part of a PA stack and said 'those are out of phase' - which they were - to the amazement of the other guys. It's hell being me sometimes lol 1 Quote Link to comment Share on other sites More sharing options...
djk Posted August 14, 2015 Share Posted August 14, 2015 Easy way to evaluate the match, hook one up out-of-phase and play noise. Face them together. The closer the match, the less you will hear. 1 Quote Link to comment Share on other sites More sharing options...
garyrc Posted August 14, 2015 Share Posted August 14, 2015 (edited) Gary, would be interested in your outcome of RTA without the Audyssey, as a true test of the similarity of the K77F. How is such a simple device so far off, even a pair of modern ones? Way back then, after being pleased with the Audyssey results -- by ear -- all around the 5.1 field, I measured just one Khorn without Audyssey, just out of curiosity. Naturally, with just the one curve, I couldn't overlay anything. This isn't what you want to know, but, even though I don't have access to that file on my old computer I remember (accurately, I think) that, without Audyssey, the K77 F was attenuated above 12 K drooping by about 5 dB at 16K (compared to the results with Audyssey). There was a hump between about 5K and 10K, where the response was a few dB louder. RE: the rest of the Khorn, at about 500 to 600 there was a little peak, then, below that, a dip between 200 and 450 or so. There was also a small, uneven peak between 100 and 200, which Audyssey, when on, knocked down. I should say that the REW microphone was not on axis, but in the centered Main Listening Position, somewhat behind where the lines coming from the two Khorn tweeters would cross. Subjectively, the K77Fs I got in the upgrade kit sounded pretty much like the K-77M (I think they were Ms -- maybe not) in my Klipschorns before the upgrade, although no two sound identical. I remember in an old Klipsch advertising booklet (8 1/2" x 11") that looked like it was from the late '60s it is stated that variations in output between tweeters of the same production lot were as much as 10 dB, and that Klipsch would test and select ones that met their standards, then create matched pairs. Maybe they are more uniform today? Edited August 14, 2015 by garyrc Quote Link to comment Share on other sites More sharing options...
babadono Posted August 19, 2015 Share Posted August 19, 2015 Easy way to evaluate the match, hook one up out-of-phase and play noise. Face them together. The closer the match, the less you will hear. Excellent idea/approach to this. Quote Link to comment Share on other sites More sharing options...
OO1 Posted August 19, 2015 Share Posted August 19, 2015 My 77 Khorns have one tweeter that is significantly weaker than the other. They have BEC AA networks so I don't think there is an imbalance there. The diaphragms are not blown as they create sound properly, just one is less output than the other. So much so that I can't listen to them without going slightly crazy. These are the round back Alnico tweeters btw. Here's what I propose to do about it. Gather up 5-6 K77's on my work bench. Fire them each up individually using an AA network, using pink noise and phone RTA, also music and my ears To determine the best matched set, then reinstall them in the Khorns. Any issues with this methodology? Failing this, I might just spring for new K77F's, I think the AK5(?) total rebuild kits are out of my price range for now. M could be just a weaker alnico magnet Quote Link to comment Share on other sites More sharing options...
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