I found an interesting problem today in a three way crossover. It was donated to me so I was doing sweeps to determine it's response (@8ohms). The load was purely resistive through the audio band so everything should have gone farely smoothly, but I noticed at around mid-band a ringing could be heard coming from the test setup. Like any good nerd I immediately assumed a coil was ringing, so I potted them by injecting low viscosity glue into the windings. Next day same thing, ringing! To find the problem I found the peak frequency (~3kHz) and turned up the voltage for a nice loud ring. Then I used my sound pressure meter to find the offending coil. Turns out the coils were silent, it was a cap that was singing! Little bastard. At only a few volts input it was puting out 94dB @1". I've attached the response plot and a photo of the pcb. The offending cap is the one in the top left (orange).
It's a cheapo unit of course but I've never heard of this happening at audio frequencies before. Anyone else have similar experiences?
It's a cheapo unit of course but I've never heard of this happening at audio frequencies before. Anyone else have similar experiences?
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