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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
 
I have a love/hate relationship with puzzles like this. On the one hand I love em because it is nice to think they can be solved if only you know enough. On the other hand I hate em because you never can be sure you are getting the whole story. Like, one train leaves at 30mph, another at 40, how many painters does it take to earn $40?  

In this case I can't help wondering, how on Earth did two speakers go bad at the same time? In other words maybe zero ohms is a red herring. No trains left the station. Three buckets of paint, and the waitress earned a $40 tip?
imhififan's avatar
imhififan
2,182 posts
 
The formula for parallel resistance is 1/Rt= 1/R1+1/R2+1/R3....  
https://www.electronics-notes.com/articles/basic_concepts/resistance/resistors-in-series-parallel.ph...

Since he measured almost 8 ohms then the total resistance will be 1/8 ohm + 0 ohm or 0.125ohm.  
If any one or more of the paralleled resistor is 0 ohm, it is a short circuit and the total resistance should be 0 ohm.

willcycle
46 posts
 
The correct formula for two resistors in parallel is Rt = r1 X r2 /(r1+r2)
erik_squires
16,058 posts
 
The best way I know of to test a crossover is to generate an impedance graph. You can use DATS V2 (or is it now up to V3) or you can build a jig and use Room EQ Wizard’s app for this.

But... if you are bi-amping it is possible the two crossover sections are not properly separated. If the voltage in one section can touch the voltage in another, at all then you can cause the amps to fight each other. If the internal crossover is completely separated, including separate grounds internally then no problem.

OTOH, if the ground is not separated internally and 1 amp has reversed outputs or balanced outputs then you run into the problem above.
fiesta75
1,378 posts
 
@likklegerry - Anymore info from you? Are you using internal passive crossovers?
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