This question is aimed to TRUE Elec Engineers, not fuse or wire directionality believers.
@rodman99999 I'm not saying the tweeter was not damaged. I am saying it was damaged for a different reason than the capacitor not doing what caps do (which is block DC). The premise that I’ve been testing, is that NO DC voltage would get past a non-polarized capacitor. At least, that’s what’s been proffered in this thread.You don't need to put a tweeter on the cap. Just put a resistor. Let it sit there for a while (the bigger the value, the longer it has to sit) and then measure the DC voltage across the resistor. There will not be any- because the cap is charged. This assumes a working capacitor of course. Capacitors, especially electrolytics, have a little bit in common with a battery. They can be charged up and hold a charge but unlike a battery, the time it takes is very dependent on the resistance in series. The tweeter was damaged because there was significant inrush current to charge that particular cap. Once charged no more current flows. That is how an exponential charging curve works. |
Same results, for a moment. BUT, now the tweeter’s blown(it literally/audibly, "popped"). Trying to read, across the tweeter’s terminals, wasn’t any more, "meaningful"(since I already knew DC voltage would pass), BUT- decidedly more EXPENSIVE! Explaining the results is easy(ie: non-polarized film capacitors, WILL pass DC).@rodman99999 OK- you didn’t damage the tweeter with a 0.1uf cap, but you did with a 33uf cap. The 33 uf cap allows for much lower bandwidth of information through the tweeter, which in most cases only handle a few watts. My surmise is the 33uf cap made for too much excursion. Caps charge along something called an exponential curve. At the beginning of the curve a lot of current flows and not so much at the top of the curve. The **amount** of current that can flow has a lot to do with the value of the cap! 33uf is a lot more than 0.1uf and so the additional current was enough to do the tweeter in. IOW that fact that you were able to damage the tweeter does not say anything about how a tweeter would pan out in a properly designed crossover. If we do the math: F = 1/C x R x 2Pi Where F is frequency C is capacitance and R is resistance To make this formula easier to use, because Farads are a lot of capacitance, we will use Microfarads (uf); so we can replace the 1 with 1,000,000 and that will give us the Frequency in cycles per second. So: 804Hz = 1,000,000/33 x 6 x 6.28 With a 0.1uf cap, we get 265KHz. IOW, a **lot** more energy was allowed to pass through the tweeter with the larger cap. Most tweeters need to be crossed over pretty high- 5KHz is common and for that a 5uf cap would suit. See if you can damage the tweeter with your battery and a 5uf cap. You can’t, because the cap allows only about 1/6 as much energy before current stops flowing. This is the tip of the iceberg here. But the bottom line is that tweeters survive output transistors shorting in the power amp quite easily- unless the crossover cap isn’t rated to handle the resulting DC voltage and is thus damaged by it (speaker manufactures don’t like to ship boxes around any more than they have to so they make sure to put in crossover caps with a high enough voltage rating). To put myself through engineering school I worked in several consumer electronics service shops and repaired many speakers damaged by shorted output transistors. IOW, I replaced **woofers**. When the amplifier clips but is otherwise damaged, that’s when tweeters fail, as the clipping generates harmonics that the crossover can’t block. The tweeter is damaged by the great power of the distortion harmonics. The solution in most cases where this is seen is to get either a more powerful solid state amp or get a tube amp (which makes less higher ordered harmonics). |
@rodman99999 Without a load it will appear that the cap is passing a voltage in your example. The voltmeter, which is typically 10 megohms, is high enough impedance that it will appear as if the cap is passing voltage, but if there were any significant load you would not see anything like this. In fact a non-polar will block DC quite effectively- and protect a tweeter from DC coming from an amplifier. The problem with non-polar caps is that they are actually two electrolytics in series. As a result, they make distortion in both directions since electrolytics can draw considerable current if reverse biased. Now if you took two electrolytics and put them in series ('back to back', so to speak, which is how a non-polar is built) but then **also** biased their junction with a DC voltage, as long as the AC waveform going through them has less amplitude then the DC voltage (thus keeping them forward biased) they can be as low distortion as a good film cap. Electrolytics have a bad reputation as coupling caps but they can work quite well if one understands how they work. |
Has anyone used one of these before:Not used it but I see no reason why it shouldn't work just fine. |
