[Elecraft] RF hardening a computer speaker.

[Jim Brown]

>I personally have not found beads to be effective even with coiling.
>On the other hand, I have found toroidal cores to be extremely effective.

Yes. The lower the frequency of the interference, the more turns you should
use around the toroid.  The higher the frequency, the fewer turns you should
use. 

>Many recommend a 0.01 uf across the speaker leads.  DO NOT DO THIS.  We
>are years beyond the old tube era and many solid state audio devices just
>hate working into capacitive loads.  If you have a 0.01 uF across the
>leads, get rid of it.  You can really blow a high power stereo easily
>with this capacitor trick.

Horse pucky. This hasn't been true for at least three decades. Any power
amplifier that won't work into a 0.01 uF load is a HUGE design mistake. 

But DO replace any zip cord that you might be using as loudspeaker cable with
twisted pair. Twisting is VERY helpful in reducing RF pickup on loudspeaker
wiring. Yeah, I know that many of the high futility speaker cables  are zip
cord, but the folks who sell them are MARKETING folks, not engineers. 

But none of this is his problem -- they are amplified loudspeakers, probably
terribly shielded. 

Jim Brown   K9YC
http://audiosystemsgroup.com