Short circuited speakers

elgee · 2nd February 2012, 09:48 AM

Hello there. A friend of mine is offering me a pair of Kef speakers that he short circuited when he was trying to pair them up with 2 other speakers. He says that one of the drivers has stopped working so he is offering them to me on the cheap. I can replace the driver if that is the problem but could there be anything else that's blown, like the crossovers? Thanks

system7 · 2nd February 2012, 10:07 AM

Technically, I don't think it's possible to short-circuit a loudspeaker.

What's more likely is the amp has got into trouble driving a horrible load or simply been overdriven. What happens next is unpredictable, but a crossover driving an open circuit speaker goes haywire with the resonant load which behaves near short-circuit. Crossover is easy to fix with standard parts. The tweeters and bass units depend on availability, but probably not cheap. It would be hard to say if the tweeters are fried without testing.

FWIW, you should never test a bass unit through a crossover with tweeter disconnected, or vice versa. Better to remove drive units for testing individually. A 1.5V battery across the speaker terminals tells you a lot. So does a resistance meter. I think you are taking quite a risk buying them in unknown condition, and since he is a friend, it's not unreasonable to have a close look first.

elgee · 2nd February 2012, 10:21 AM

Thank you system7. I've only spoken to him on the telephone because he lives quite a distance away. Is there anything I could ask him to do by way of simple checks that might give me a better idea of what's wrong?

system7 · 2nd February 2012, 10:32 AM

You need to know if it's the bass or the tweeter (or the midrange in some speakers...) that has failed. It's nice to know the model too, to assess spares prices on what will be specialist KEF units. I expect those co-axial full-range units are pricey.

It's OK to give them VERY low volume through the amp to test that. High volume will not do the amp any favours, and possibly damage it for the reason of the crossover becoming resonant.

A blown tweeter might be expected here, and not be very serious to replace. A blown woofer would suggest a more serious accident IMO. I don't know if these units will have simple fuses that might have popped.

elgee · 2nd February 2012, 12:55 PM

I'll phone and ask him for more info. I think I'll have to see them for myself to guage damage etc. Thanks again for your help.

2nd February 2012, 09:48 AM	#1
elgee diyAudio Member Join Date: Oct 2011	Short circuited speakers Hello there. A friend of mine is offering me a pair of Kef speakers that he short circuited when he was trying to pair them up with 2 other speakers. He says that one of the drivers has stopped working so he is offering them to me on the cheap. I can replace the driver if that is the problem but could there be anything else that's blown, like the crossovers? Thanks

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2nd February 2012, 10:07 AM	#2
system7 diyAudio Member Join Date: Aug 2008	Technically, I don't think it's possible to short-circuit a loudspeaker. What's more likely is the amp has got into trouble driving a horrible load or simply been overdriven. What happens next is unpredictable, but a crossover driving an open circuit speaker goes haywire with the resonant load which behaves near short-circuit. Crossover is easy to fix with standard parts. The tweeters and bass units depend on availability, but probably not cheap. It would be hard to say if the tweeters are fried without testing. FWIW, you should never test a bass unit through a crossover with tweeter disconnected, or vice versa. Better to remove drive units for testing individually. A 1.5V battery across the speaker terminals tells you a lot. So does a resistance meter. I think you are taking quite a risk buying them in unknown condition, and since he is a friend, it's not unreasonable to have a close look first.

2nd February 2012, 10:21 AM	#3
elgee diyAudio Member Join Date: Oct 2011	Thank you system7. I've only spoken to him on the telephone because he lives quite a distance away. Is there anything I could ask him to do by way of simple checks that might give me a better idea of what's wrong?

2nd February 2012, 10:32 AM	#4
system7 diyAudio Member Join Date: Aug 2008	You need to know if it's the bass or the tweeter (or the midrange in some speakers...) that has failed. It's nice to know the model too, to assess spares prices on what will be specialist KEF units. I expect those co-axial full-range units are pricey. It's OK to give them VERY low volume through the amp to test that. High volume will not do the amp any favours, and possibly damage it for the reason of the crossover becoming resonant. A blown tweeter might be expected here, and not be very serious to replace. A blown woofer would suggest a more serious accident IMO. I don't know if these units will have simple fuses that might have popped.

2nd February 2012, 12:55 PM	#5
elgee diyAudio Member Join Date: Oct 2011	I'll phone and ask him for more info. I think I'll have to see them for myself to guage damage etc. Thanks again for your help.

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