This question is aimed to TRUE Elec Engineers, not fuse or wire directionality believers.

1.5V across 6 Ohms = 0.25A or 0.325 Watt

Correction:
1.5V across 6 ohms = 0.25A or 0.375 Watt

I think the current is pass through the tweeter voice coil and charge up the cap, if there's 80VDC the voice coil will blow in seconds.

Conducting an experiment(yesterday) with a Speakerlab W1048P, 10" woofer(two layer, 2", 10mm overhang voice coil, 200W power handling), with only the C cell and 33uF Clarity ESA, produced a pronounced pop, at the moment the battery was connected(iow: a DC voltage spike). The first time I tried that with the tweeter(cap/C cell/tweeter/in series), the spike was sufficient to take out the tweeter. Removing the battery and discharging the cap into the driver, produced the same transient(rhetorical). As far as the amount of juice, provided by a C cell: without the capacitor, it was sufficient to hold the woofer at it’s full, linear(10mm, measured) excursion, as long as I kept it connected(also- rhetorical, but- the tweeter couldn’t take it, even through the cap). Wish I hadn’t sold my O-Scope. I could measure the transient’s actual time/voltage(if frogs had wings....). I have little doubt, variations in capacitor values(uF/VDC), would alter the results(at least regarding duration).

My apologies to the OP, for the departure from their basic query.

Thanks for the additional datapoints, Rodman. I don’t think the pronounced pop at the moment the battery was connected (or when the cap was discharged into the driver) is surprising. For a theoretically ideal capacitor i = C(dv/dt), of course, ("i" = current; "C" = capacitance; "dv/dt" = change in voltage per unit time), so completing the circuit by touching wires or leads together would result in a nearly instantaneous change in the voltage applied to the cap, resulting in a large (dv/dt). And discharging the cap into the driver would have similar consequences, as the voltage across the charged cap would abruptly be forced toward zero by the low resistance of the paralleled driver.

But in the event of an amp failure resulting in a large DC output, how likely is it that the DC voltage will be ramped up in a comparably abrupt manner? I don’t know the answer to that.

And what I don’t understand in your latest results is how the C cell could hold a 200 watt woofer at full excursion. Even if the DC resistance of the driver is as low as 2 ohms, the battery would be putting not much more than 1 watt into it. And 200 watts into any reasonable woofer resistance corresponds to vastly more than 1.5 volts, of course.

Also, it seems relevant that the capacitors used in many tube-based preamps and other tube-based components to couple the signal at the plates of various interstage and output tubes to the grids of a subsequent stage or to the input of another component, such as a power amp, are in many cases used to block DC on those plates of well over 100 volts (at least if a cathode follower is not used, in the case of output stages). Yet that never seems to be a problem. And in many cases those caps have values that are not much different than the 0.1 uF cap Rodman experimented with. And I seem to recall that some McIntosh designs, at least, have used fairly large electrolytics for their output coupling capacitors, having values not all that much lower than the 33 uF he also experimented with.

Finally, although it’s more of an academic point than one having practical significance, if a large DC voltage is suddenly applied to a capacitor, and a large current briefly flows corresponding to C(dv/dt), the nearly instantaneous change in voltage means that spectral components are present at non-zero frequencies, at and near that instant. Which by definition means that the voltage is not DC, at and near that instant.

Regards,
-- Al

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).