I have a pair of old speakers that I'd like to magnetically shield for pratical uses.

I've looked up some method but I'm not quite sure which is best;

---Using some foil like "MuMetal" to attache on the inside of the speakers (which I have access to, lucky me). I'd also like to know how that is done, with some kind of glue or more drastic? And how many layers for a proper performance, (minimal distortion)?

---Or the use of another magnet, illiminating the emitted field by the drivers? And how does one install that? How good is that?

---Or another method?

---Or should I forget all about it, because these installment will interfere with the proper functioning of the speakers and their resonance?

Won't somebody clarify this matter?