How to test for defective speaker?

[fvoelling]

My center speaker appears to be defective, but I have no idea on how/what to test. Here's the situation.

My Rotel receiver shuts down (goes into protective mode) during certain movie scenes when played at high volume levels (80 on the volume scale of the Rotel). I can repeat this at will. Swapping the center speaker's cable to one of the (bigger) main front speakers or one of the (smaller) surround speakers plays the same scene just fine.

Problem is, just listening to the center speaker by itself doesn't reveal any obvious problems (e.g. blown tweeter). The company that makes the speaker hasn't responded to my calls (rumors have it they've gone out of business).

Any ideas?

Thanks,
Frank

[Kevin P]

What kind of speaker is it? What's its impedance and efficiency rating, compared to your other speakers? Perhaps it's overloading your amp, or you have a short somewhere. Have you tried the center in place of one of the mains to see if the problem happens there?

You would hear it if you have a blown driver. More likely it's a short or the amp being overloaded.

[ThomasW]

If the protection circuit is a bit extra sensitive, and the speaker's crossover is a bit flaky that could be the problem.

Just guessing but a cap going bad in the crossover might cause this.

[fvoelling]

These are the speakers in question:

Center:
Soliloquy C-3, 8ohms, 89dB, 45Hz-20kHz, 8-220W

Mains:
Soliloquy 5.3, 8ohms, 90dB, 35Hz-20kHz, 8-300W

Surrounds:
Soliloquy SAT 5, 8ohms, 87dB, 60-20kHz, 15-150W

Seems like the center falls right in between the other types (both of which work in place of the center) in terms of efficiency, power handling, etc. No, I haven't tried putting the center in place of one of the mains, I'll give that a shot tomorrow.

Frank

[fvoelling]

Tested with center and front right speakers switched, no problems.

Put the center back in its original position, fails every time with the volume control set to 80, but worked ok when I tried it a couple of times at 78.

BTW, the scene I'm playing is at 34:45 in "Batman Begins" when the loud sword noise starts.

I don't have any electronics background whatsoever, but I mentioned the possibility of a bad capacitor to my father-in-law and he said I can test the capacitor(s) with a meter (something about going to 0 and then infinity if it works, otherwise it "leaks"). Next step is opening up the speaker to see if I can get the x-over out.

Frank

[fvoelling]

OK, took out the crossover and measured resistance across each of the two caps. Neither one is marked in any visible way, but one measures 3.7 ohms and the other shows 0L, meaning either nothing is connected to the meter, there's an open, or the resistance is so high that it overloads (>4M ohms).

Does that sound like one of them is bad? What's the "normal" reading for a capacitor? BTW, these were measured inside the circuit, not disconnected from the crossover as they are soldered.

[Stoney]

Pretty tough to test a cap in circuit. Basic definition of the function of a cap is that it blocks DC and passes AC. Hence the metheod of using an OHM-Meter to check it. If you put the meter across the cap, it will charge to the DC value of the battery of the meter, at which point no more current will flow and the meter will show a high resistance. While it is in the circuit, there could be current paths through other components of the circuit.