Testing speakers?

Roel

Roel

That SMART guy.
How do you do that? In our youthclub, we have 4 speakers that are defect. Either no highs (tweeter cooked), no lows (speaker), or no sound at all (euhm... I'm guessing the cable :D ).

So how do you go when testing them for ordering new parts?

I can try them seperately, just connect one speaker at the time, and listen on low volume what speakers are working? Is that the way?

The speakers have a passive crossover in them. Any chance that these are broken? How do I check that? Anything I can do with my digital multimeter?
 
If they're moving coil type speakers (as apposed to something like a piezo tweeter) you can ohm them out witha VOM. Granted this will only tell you if the voice coil is shorted or opened, it's a good place to start. Resistance will typiclly be within a few ohms of the stated impedence (an 8 ohm speaker might give a resistance reading of 4 to 6 ohms although this isn't exclusively true). You can weed out the ones that are blown to shit this way. Anything beyond that (distortions due to bent/damaged voice coils), you'll have to hook them to an audio source and listen to them.
 
Just check them one at a time. You'll know it's the crossover if the spkr works direct, if not, it's the spkr. But it could also be both.
 
I sometimes use a an AA or a AAA battery. Just connect each wire of the speaker to each terminal on the battery. You should hear a click when you do this. If you don't the speaker is bad. I have done this a thousand times (even on small speakers) and it doesn't seem to hurt the speakers.
 
Djc, I do this all the time to determine the polarity of a speaker if it's not clearly marked (positive voltage on the positive lead of the speaker makes the excursion come out towards you). I've never harmed a speaker doing this.
 
A 1.5V battery is fine for checking polarity or testing for catastrophic failure, but it won't necessarily tell you if the speaker is "half baked". A sine wave from a synth would be a little more informative - high notes for the tweeters, low notes for the woofers. Everything should sound nice and smooth.

Test the drivers individually first. If they seem ok, then the most likely candidate is a blown protection circuit or fuse. Baring that, it's probably a bad electrolytic capacitor in the crossover network. You can test them with a tweeter like this:
Code: 
           [   ]+------||-----+
           [   ]       cap    |
[synth]----[amp]             (|< tweeter
           [   ]              |
           [   ]---------------
You don't have to actually remove the cap to test it, but make sure no other parts of the crossover are in the circuit. Just use some alligator clip leads to connect to both sides of the cap.

Play a very high pitch note like a C8 or higher with clips connected together (cap bypassed). Then place the clips on both sides of the cap and play it again. The note should still sound clear and about the same loudness as when the cap was bypassed. If it doesn't, replace it with a matching value non-polarized capacitor.

barefoot
 
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