Would it be possible to add to the below circuit so that I could not only filter out the highs but also 60 cycle hum? I only want to hear audio in the range of a human's voice.
Speaker Noise Reduction Circuit Add on VE3VDC
Thank you in advance for any help,
yeto
Let's clear a couple things first, for a better answer.
1) are you a Ham? Is this filter meant to be used with some kind of Ham receiver/SWL/portable Communications?
2) if so, the one shown is
very crude, just not to call it useless.
Its poor slope (again an understatement) means it either can not filter noise out, or kills audio intelligibility or both.
As suggested above, you should need a
strong voice intelligibility band bandpass filter, which given the 10:1 ratio (3kHz to 300 Hz) is best accomplished by a 300Hz highpass followed by a 3 kHz lowpass; both *at least* 12dB/octave.
In fact doubling that to 24dB octave would be way better.
This can easily and inexpensively accomplished by active filtering, a couple cheap Op Amps and a few extra parts can do, but you need some way to insert it before the power amp.
If your receiver is a closed box and you have no access to its electronics, then some passive filter may be inserted between power amp and speaker, but I guess weight/size/cost/complexity will make it prohibitive.
Besides it, a tunable notch filter or a Parametric Equalizer is often used in Communications situations to tune out annoying heterodyne squeals.