Tony T Posted October 4, 2018 Share Posted October 4, 2018 (edited) I have a pretty good volt/ohm meter and need to test out a K-77 & K-55. Not sure what setting to use on the meter and what it is I'm looking for as far as a reading. If anyone could provide guidance I'd greatly appreciate it. Thanks Edited October 4, 2018 by Tony T additional info added Quote Link to comment Share on other sites More sharing options...
WMcD Posted October 4, 2018 Share Posted October 4, 2018 It would help if you can post a picture of your meter. Generally you want to measure resistance in ohms and meters indicate this by a setting a knob or button to an R or upper case Greek omega Ω. Then you need a range which allows readings, roughly, below 20 ohms. But some meters "auto range." Modern meters will have a numerical display. One issue is that "infinite ohms" or open circuit will cause the digital display to show OL or like that. You'll get it when the probes are not touching each other. The manufacturer of your meter may have a webpage with a tutorial. Otherwise there is a lot on YouTube re using meters. Any properly functioning driver will show a resistance from 4 to 12 ohms, depending on the model. One with a burned out voice coil will show that infinite reading. It is a general litmus test of the integrity of the voice coil. The voice coil is the coil of wire which sits in a magnetic field generated by the magnet structure. The electrical terminals of the driver are attached to the voice coil. Current from the amp cause the voice coil to make a magnetic field and this moves the diaphragm to which it is attached to make music If there is too much current from the amp the voice coil burns out and its resistance becomes infinite. WMcD 3 Quote Link to comment Share on other sites More sharing options...
BEC Posted October 4, 2018 Share Posted October 4, 2018 With all wires disconnected, measure across the driver terminals with the meter set to read resistance. The K-77 should read around 6 to 8 ohms. The K-55 around 10 to 11 ohms. Now, this does not tell you if the driver is good or not, just lets you see if the voice coil is open or shorted. It can read good for resistance and still have other problems that keep it from working right. 2 Quote Link to comment Share on other sites More sharing options...
Tony T Posted October 4, 2018 Author Share Posted October 4, 2018 Easily done and so far so good. Thanks! Quote Link to comment Share on other sites More sharing options...
parlophone1 Posted October 4, 2018 Share Posted October 4, 2018 5 hours ago, BEC said: It can read good for resistance and still have other problems that keep it from working right. Can you point out these problems or maybe provide some links explaining that? I am very interested to know more. Quote Link to comment Share on other sites More sharing options...
Chris A Posted October 4, 2018 Share Posted October 4, 2018 This is a pretty simple test device that's available from Parts Express that will tell you much more than a VOM: https://www.parts-express.com/dayton-audio-dats-v2-computer-based-audio-component-test-system--390-806 It connects to a USB port on your computer and has two electrical leads. It will plot impedance vs. frequency and rubbing/buzzing issues. It will also characterize the so called T/S parameters for your drivers. It's very easy to use and takes merely seconds to run. Chris 2 Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted October 4, 2018 Share Posted October 4, 2018 11 hours ago, parlophone1 said: Can you point out these problems or maybe provide some links explaining that? I am very interested to know more. Garbage in the voice coil gap or loose housing bolts come to mind. Quote Link to comment Share on other sites More sharing options...
garyrc Posted October 4, 2018 Share Posted October 4, 2018 17 hours ago, BEC said: With all wires disconnected, measure across the driver terminals with the meter set to read resistance. The K-77 should read around 6 to 8 ohms. The K-55 around 10 to 11 ohms. Now, this does not tell you if the driver is good or not, just lets you see if the voice coil is open or shorted. It can read good for resistance and still have other problems that keep it from working right. 17 hours ago, WMcD said: Generally you want to measure resistance in ohms and meters indicate this by a setting a knob or button to an R or upper case Greek omega Ω. Then you need a range which allows readings, roughly, below 20 ohms. But some meters "auto range." Modern meters will have a numerical display. One issue is that "infinite ohms" or open circuit will cause the digital display to show OL or like that. You'll get it when the probes are not touching each other. Any properly functioning driver will show a resistance from 4 to 12 ohms, depending on the model. One with a burned out voice coil will show that infinite reading. It is a general litmus test of the integrity of the voice coil. ... WMcD About what resistance should a Klipschorn (AK4) be when measured as a whole through the crossosver network from the amplifier end of the speaker cable (disconnected from the amplifier, of course)? I think we need a new, cheap VOM. We had one from Rasio Shack for about 15 years that was fine, and it was lost in a move. Just before RS disbanded they sold us another one in which the needle bounces around a lot when measuring resistance or volts. The resistance reading surprised me, but I have no idea how the crossover and all three drivers, all in their normal configuration, should measure. Both Khorns measure about the same (but the needle bounces/drifts). They sound fine, and have for a period of several years since we installed the AK4 kit. The amplifiers are not protesting. Quote Link to comment Share on other sites More sharing options...
BEC Posted October 4, 2018 Share Posted October 4, 2018 If you measure on the input terminals with it disconnected from the amp, you would essentially be just measuring the resistance of the woofer voice coil and one inductor in series with that woofer. Should read about 4 ohms. The bouncing around would be from sound in the room moving the woofer cone some generating a bit of voltage as it moves the coil inside the magnet. Bob Crites 3 Quote Link to comment Share on other sites More sharing options...
WMcD Posted October 5, 2018 Share Posted October 5, 2018 There are situations where voice coil resistance as tested with a meter looks good at about 8 ohms but the woofer has a muffled sound. We must remember that the voice coil is wound on a cylinder of paper or Kapton (sort of heat resistant paper) and it is all held together by some sort of glue. This sits in circular iron gap which has an intense magnetic field. You can find plenty on this on the Internet. The former is mechanically connected to the diaphragm and the spider and edge of the diaphragm keeps everything in alignment to allow the diaphragm to move smoothly. One mechanical issue is that there must be nothing in the gap to jam the former from moving. So, what could go wrong? One thing is that when too much current is sent to the voice coil, the wires could melt and the measured resistance goes to infinity. This is shown by the typical multimeter test. Not a jamming issue. Although somewhat rare, there are situations where the voice coil has gotten hot enough to fail the glue and the former gets warped and therefore jams in the gap. The voice coil is not burned out and electrically tests good but the suspension is jammed. You can detect this by using an open hand to move the diaphragm. I found this on a young relative’s book case speakers which had been dragged out to a pool party. I expect someone turned up the bass knob and the loudness. I cut open the woofer with an Xacto knife and found charring. ("Should you be caught or killed, the Secretary will deny all knowledge of your actions.") My relative denied . . . Another situation arouse in my old Volvo where I put 6 x 9 ovals in the doors. Rust had migrated into the gap. Overall, I think these sort of things rarely happen to a tweeter. The windings are of such thin wire that they just fail by melting. Tweeters are good for about 5 watts continuous, if that. Midrange, I don’t know. They may be good for 40 watts continuous. Folks tend to fail woofers and tweeters first. Drifting off topic. Hunter told a story where a plastic based driver melted rather than electrically failed, or at least melting happened first. In another situation a pro speaker configuration was hooked up to a kilowatt of amplifier and caught fire from being over driven. 1 Quote Link to comment Share on other sites More sharing options...
Deang Posted October 5, 2018 Share Posted October 5, 2018 The K-55-V and K-55-X have AlNiCo magnets. They can demagnetize via rough handling (dropped, banged together), or when exposed externally to high currents. They should not be stored sitting in close proximity to one another. A diaphragm can test good with a meter, but show poor response when tested with more sophisticated gear. Quote Link to comment Share on other sites More sharing options...
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