In article ,
Bob Mannix wrote:
All the responses so far have assumed an amplified hum signal. This unit
has a built in amplifier and it's possible the mains transformer for
the power supply is physically humming/vibrating as it is loose or has
become so and it's nothing to do with leads, connections etc. This
would sound like it was coming out of the speaker.

In this context they don't usually produce 50Hz but more of a buzz. They
can produce low frequencies when attached to a large resonant panel but
I'd say a speaker maker would avoid this.

--
*A conclusion is the place where you got tired of thinking *

Dave Plowman London SW
To e-mail, change noise into sound.