Extremely cautious measures taken🙂 80 uF cap and an L-pad. Unfortunately, I had 8 ohms only, so not that ideal. I will maybe try to add a resistor in parallel with the driver.
As we know, a fraction of a watt (95dB or less at a meter midband) would not have damaged the drivers.
If DC were the problem, you would have heard a loud "clack" sound both when you hooked the driver up and when it was disconnected.
It sounds like the drivers had been damaged (perhaps by a company doing destructive testing), reboxed, returned for repair, then accidentally shipped out as new.
Or gremlins did it..
At any rate, a capacitor and L-pad resistor in series (or a resistor in parallel) will change the response of a driver considerably in nearly every measurable aspect.
Yes, really strange. No real power went into the drivers under my control. And no other drivers got harmed using the same process/amp. This is just for the start when they get back. I will need to pad the driver sections anyway, this is just for the start.
The drivers are finally back from the factory with brand new membranes (many thanks to BC for that). I saw some pictures, not sure what I was actually seeing, but the old membranes were told to be smashed and mechanically damaged - they looked like they suffered severe overload - which is just impossible from Clio Pocket sweeps at bearable volumes.
The only possible reason I can think of is that the drivers were damaged when connected to the test amplifier before it was turned on - and were damaged by the transient at turn on. The funny thing is, no other drivers were damaged by the same amplifier and the damage did not get worse during the measurements I made when I found out this problem - I repeated the measurements quite a few times before I put them on claim.
Actually, there might be another possibility - although I am sure I have not heard anything unusual while measuring the drivers. I might have swapped the input and output of the Clio pocket and have the phantom power for the microphone turnes on. If the amp was DC coupled, I could get constant DC at the output - but I am not sure this is even possible at all. And the voice coils would have beem cooked, but that was definitely not the case.
Or maybe a 50 Hz induced hum on the output would not be heard, but smash the membranes? But there were no audible signs of that like clicking or anything.
Anyway, I will pull out a scope to test these hypotheses above if I can see anything dangerous at the output of this particular amplifier. It is now officially on the black list and will not be used until proven to be safe. If proven to be safe, it will go for sale.
The only possible reason I can think of is that the drivers were damaged when connected to the test amplifier before it was turned on - and were damaged by the transient at turn on. The funny thing is, no other drivers were damaged by the same amplifier and the damage did not get worse during the measurements I made when I found out this problem - I repeated the measurements quite a few times before I put them on claim.
Actually, there might be another possibility - although I am sure I have not heard anything unusual while measuring the drivers. I might have swapped the input and output of the Clio pocket and have the phantom power for the microphone turnes on. If the amp was DC coupled, I could get constant DC at the output - but I am not sure this is even possible at all. And the voice coils would have beem cooked, but that was definitely not the case.
Or maybe a 50 Hz induced hum on the output would not be heard, but smash the membranes? But there were no audible signs of that like clicking or anything.
Anyway, I will pull out a scope to test these hypotheses above if I can see anything dangerous at the output of this particular amplifier. It is now officially on the black list and will not be used until proven to be safe. If proven to be safe, it will go for sale.