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
ps,just found this in an old book
7.1ohms LEFT MID/HIGH 8+6.4=4+3.2=7.2
6.8ohms LEFT Bass 6.8

7.0ohms RIGHT MID/HIGH 7.5+6.5=3.75+3.25 
6.8 ohms RIGHT Bass 6.8
i must have taken these measurements of the speakers a few years ago,which are different to the measurements that we have now,i know these are the measurements as i only own one pair of bi-wirable speakers
If you measure the resistance across the loudspeaker posts which include connection to the bass driver (or full range) then you will measure some resistance that is greater than 0Ω which is made up of the crossover components and the voice coil resistance of the bass driver only. You are not measuring the impedance of the loudspeaker, in fact an impedance measurement doesn't mean anything unless you know the frequency you are measuring at.

In your configuration you should see open circuit for MF/HF and some resistance across LF. Which you do when the crossover is disconnected from the speaker terminals.
If I understand you correctly it is only when you put the loudspeaker back together that you read 0Ω across the MF/HF. If that is correct then you have a short which is upstream of the crossover i.e. the loudspeaker terminals, connecting wires etc.
If the MF/HF connectors really are a dead short then your amplifier would fail immediately... actually it should go into overcurrent protection but I digress.

Something doesn't add up.

1) You measure 0Ω across the MF/HF terminals of both speakers.

2) When you had everything disconnected you measured open circuit across IP+ & IP-. That is what you would expect.

Knowing that, it should be simple with the crossover disconnected to measure the resistance across the loudspeaker terminals to locate the short. If there's not one then the short was either at the point the wires connected to the crossover or items 1 & 2 listed above are incorrect.

The fact that both speakers measure 0Ω at the MF/HF terminals implies that you're not looking for a stray wire or small solder bridge but a mistake or failure on both speaker inputs. That's why something like connecting the amplifier outputs incorrectly seemed like a likely scenario... although I know you've ruled that out.



thankyou for that,some thing seems a miss,i do read 0ohms,i also found my orignal written values also this morning when i first started investigating all this,
Tell you what,you guys have put so much time and effort into this,this weekend i am going to clean everything up and start again,i will take variuos readings on crossovers,re-assemble the whole two speakers and do it all again and then i will come back with a list of readings,it seems thats all i can do,i really appreciate all the help,i really do.
And thank you all again
Mk
where i have written"   speaker terms with everything connected" ive written Hi and low, which means mid/high and bass,on the speaker posts,just to clear that.
thanks guys