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testing a crossover

hi guys and girls i have a
problem with my 3 way  wilmslow-audio mirrage speakers , I am hoping you can help me with the problem,.
Lately my power amp went pop and i sent it away for repair,when i
received it back {repaired} it went pop again,on sending it back to
the repair technician ,he has come back to me ,and asked me to take
some ohms readings on the speakers, on testing the speakers , i run
these speakers using 2 power amps{Arcam Alpha 10s,using one for low
pass{bass} and the other for MID/HIGH,this is the amp which keeps
blowing,on the high /mid,on testing the terminal the bass{low pass}
read {left speaker]7.9 ohms ,right speaker bass 6.8ohms, But on the
left and right speakers hi/mid ,both read 0.0 ohms,{which we all know
is wrong}
BUT the strange thing is,when the blown amp was away,i only used one
power amp to run both speakers in bi wire config,and they worked
ok,all being a bit lack of bass and tightness,but still sound great.
So i stripped both speakers and checked the drivers,all 6 drivers
where good no shorts reading approx correct ohms for age,{Speakers
disconnected from x over}.can any one help with this,i would be so much in debt.
kind regards Mark
likklegerry
millercarbon's avatar
millercarbon
12,531 posts
 
You have a dead short. They worked when connected normally because then the amp sees the sum total resistance including the 6.8-7.9 ohms. But connected bi-wire one amp sees only a dead short and so pop, there she goes.

The lack of bass and definition is because the dead short results in a total impedance much lower than 6.8. It is simply running out of gas and so what seems strange to you is perfectly normal and expected given the situation.

Now it seems something happened to create the dead short. This is what caused the pop and the first amp failure. It seems the drivers are putting out sound or you would have noticed that, and they measure fine. So probably the short is somewhere between the terminals and the drivers. That leaves wires and crossover.

Get in there and see. (I hope it is not one of these potted crossover situations....)
fiesta75
1,378 posts
 
I agree with MC's dead short analysis. Are you b-amping using the passive crossovers inside the speakers, or are you using an active crossover at the inputs of each amplifier? If you are using the passive crossovers in the speakers, then there could be a short in the crossover. But, that doesn't explain why it works when you go back to driving with a single amp. Let me think, and I might have more suggestions once you get back to us.
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cleeds
6,009 posts
 
millercarbon
You have a dead short. They worked when connected normally because then the amp sees the sum total resistance including the 6.8-7.9 ohms. But connected bi-wire one amp sees only a dead short and so pop, there she goes.
Nope. You're confusing bi-wire with biamplification. They are two different things.
In biwire configuration, the amplifier still sees the drivers' total resistance.
fiesta75
1,378 posts
 
Okay so MC said bi-wire and not bi-amp, big deal, I knew what he meant. At this point we know there's a short somewhere. Could be shorted caps, but we need more info.
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