In article ,
Scott McDonnell wrote:
Hello,

My father owns a few resturaunts and these use 70V commercial sound
systems for the background music. In one of his stores, the speakers
are making a crackling or popping sound all of a sudden. He asked me
to change 3 speakers (they were in quiet areas where it was most
noticeable so he thought that was all it was) and the problem is
still there, even in the new speakers. I started suspecting the 70V
amplifier. He had a spare one, though it was used and about as old,
so I installed that one to see if there was a difference. The
crackling was still present. Anyone have any ideas what to check
for?

So far, I have tried:
replacing a few speakers
tried a different, but not new, 70V amplifier
tried different wattage settings at the speakers
tried to adjust the volumes on both amp and source
balanced bass and treble

None of this seems to work. I do have an oscilloscope
and know how to use it, but have not had a chance to
bring that with me and look at the signals. Any suggestions?

Using my theory of maximum inconvenience, it'll be a simple problem
in the hardest part of the system to fix. The wiring in the walls.

Is there a remote volume control panel? If it's on all the speakers,
it sounds like an intermittent on the input side of things. Or pickup
of radio transmitter. (Any highway patrolmen radioing in after they
finish lunch?. Somebody on the other side of the wall running real
estate deals on his cellphone)?

Mark Zenier Washington State resident