Peter P. Posted May 5, 2023 Share Posted May 5, 2023 I'm doing minor work on a used pair of Avid 100s I bought. Doing my research I found the factory crossover point is 2500Hz and elsewhere verified the factory capacitor value is 2 microfarads. While I was hearing output from the tweeter, it was only by performing the cardboard tube test (and it does not appear it's the factory tweeter although the resistance value is correct). I was suspicious something was amiss. Since there's only a simple capacitor in the crossover I used an on-line crossover calculator to confirm the capacitor value and here's what I found. Factory value: 2 microfarads What's in the speaker: 2 microfarads The on-line calculator results: 8 microfarads From the on-line calculator that 2 microfarads should yield a whopping 9.5kHz crossover! What's going on here? Maybe the factory tweeter has higher output? Why the discrepancy in capacitor value-a factory change to protect the tweeter from being over driven? I'm not going crazy on throwing money at these speakers but using this as an educational experience. Link to comment Share on other sites More sharing options...
mboxler Posted May 5, 2023 Share Posted May 5, 2023 1 hour ago, Peter P. said: I'm doing minor work on a used pair of Avid 100s I bought. Doing my research I found the factory crossover point is 2500Hz and elsewhere verified the factory capacitor value is 2 microfarads. While I was hearing output from the tweeter, it was only by performing the cardboard tube test (and it does not appear it's the factory tweeter although the resistance value is correct). I was suspicious something was amiss. Since there's only a simple capacitor in the crossover I used an on-line crossover calculator to confirm the capacitor value and here's what I found. Factory value: 2 microfarads What's in the speaker: 2 microfarads The on-line calculator results: 8 microfarads From the on-line calculator that 2 microfarads should yield a whopping 9.5kHz crossover! What's going on here? Maybe the factory tweeter has higher output? Why the discrepancy in capacitor value-a factory change to protect the tweeter from being over driven? I'm not going crazy on throwing money at these speakers but using this as an educational experience. Poking around on the Web, it looks like there is a switch on the front to control the tweeter? Perhaps it's a variable series resistor to pad down the tweeter? Also, sounds like the original capacitor was a 2uf non-polar electrolytic. If so, it's probably dried out and not functioning properly. I'd replace the capacitor with a 2uf polypropylene, and check the switch to make sure it's not faulty. BTW, a 2uf capacitor at 2500hz is around 32 ohms. The switch could be adding 24 ohms to an 8 ohm load to achieve that crossover point. Mike Link to comment Share on other sites More sharing options...
CWOReilly Posted May 5, 2023 Share Posted May 5, 2023 Any switches or tone controls should be cleaned. Is the tweeter low on both? If not swap the tweeters around. Link to comment Share on other sites More sharing options...
Peter P. Posted May 5, 2023 Author Share Posted May 5, 2023 I measured the tweeter's DC resistance and it's in spec. The capacitor measures 1.9 microfarads so it should be good. I don't have an ESR meter to test with so I can't compare. The tweeter does have a level switch. It measures 0, 8, or 16 ohms depending on the switch position so I know it's functioning, you can see the wire wound resistors in the switch circuit, and I did clean the switch. I barely tell the difference in any position but the tone generator I used below shows different levels of load equivalent to +3 and -3dB from a nominal position. I did put my voltmeter across the input leads while driving the speaker and there's definitely voltage across the terminals and like I said, using the cardboard tube test I do hear audio. I'm wondering whether the the non-OEM tweeter has different characteristics such as lower output level. I did grab my test tone generator from work and applied test tones to the tweeter; the driver is definitely working. Link to comment Share on other sites More sharing options...
mboxler Posted May 5, 2023 Share Posted May 5, 2023 What DC reading did you get? Sounds like you need a larger capacitor. Link to comment Share on other sites More sharing options...
JohnA Posted May 8, 2023 Share Posted May 8, 2023 As in the old Type A Klipsch crossover, a 9 kHz theoretical crossover point is needed to protect the tweeter from low frequencies. Don't change it. What is the DCR of the tweeter? What happens if you use a 1.5V battery across its leads, rubbing one lead? Is its output similar to the woofer tested the same way? Link to comment Share on other sites More sharing options...
Peter P. Posted May 8, 2023 Author Share Posted May 8, 2023 4 hours ago, JohnA said: As in the old Type A Klipsch crossover, a 9 kHz theoretical crossover point is needed to protect the tweeter from low frequencies. Don't change it. What is the DCR of the tweeter? What happens if you use a 1.5V battery across its leads, rubbing one lead? Is its output similar to the woofer tested the same way? To answer mboxler's question above; the DC resistance of the tweeter measures 6.8 ohms although it's stamped 8 ohms which I presume is nominal. I've placed a 9V battery across the tweeter terminals (briefly!) and you can hear the "click" so I know it's working, and as in my post above, I can generate a tone (highest tone I can generate with my Lineman is 2804Hz) and it's audible to me, so I know it's working. I have NOT compared it to the woofer but from other woofer specs I've seen, these woofers likely roll off naturally just above 2kHz. I imagine I can perform the test and see if both the woofer and tweeter generate a similar level. Now it kinda makes sense to me. These tweeters are clearly not OEM as the OEM tweeters were a phenolic ring design. Midwest Speaker sells an exact replacement with a higher power handling and higher efficiency (which can be tempered by the speaker's tweeter control) so I'm tempted to replace the tweeters. And you're definitely persuading me to keep the 2 microfarad capacitor as it was OEM spec. My capacitor measurements indicate it's good and from what I've read polypropylene capacitors don't usually age like electrolytics so I should be good there. I'll report back when I get the replacement tweeters. Update: I generated test tones using my Lineman into the speaker terminal and yes; both the woofer and the tweeter reproduce the tones from 1004-2804Hz at roughly the same level using the "cardboard tube test tool ;-)". I ordered the replacement tweeters anyway. Down the rabbit hole I go... Stay tuned! Link to comment Share on other sites More sharing options...
JohnA Posted May 11, 2023 Share Posted May 11, 2023 DO NOT use a 9V battery to test a tweeter. And when testing a tweeter, keep one lead moving so it never sees DC, but gets a series of pulses that cause a scratching sound. Use only a 1.5V battery on tweeters and then, it's best only to test it in lieu of an ohm meter. 1.5V is also plenty to verify the polarity of a woofer. 9 volts across a tweeter is 10 watts, if the battery can supply the current. Many tweeters cannot tolerate 10 watts. Link to comment Share on other sites More sharing options...
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