Hi Bill,
Your a/d/s center obviously isn't shielded. An extra magnet is usually added that counteracts the spurious force fields of the speaker's magnetic assembly. Ian might have some additional information on this matter.

Years ago, a special metal called mu-metal was used to shield magnetic phono cartridges from the radiated fields of the turntable motors. But it was much too expensive to use for speaker shielding.

II recall publishing an item in the very early days of Home Theater (early 1980s) about using a sheet of "cold, rolled steel" that you could place under a speaker to prevent interference with the picture tube. I'll look in my files and see if I can root out the gauge of steel you had to use. . .

Alan Lofft
Axiom Resident Expert

Alan Lofft,
Axiom Resident Expert (Retired)