How shielded are sheilded speakers?

I want to build the below but with a marine speaker and a waterproof case to take canoeing. Worried that my Zune has a hard drive and the speaker magnet might wipe the HD. Can I let my Zune within 6" of one for mounting purposes inside the box?

https://www.instructables.com/id/Simple-iPod-Amp/

I'm going to say no. Smarter people than I may say I'm wrong, but I think you stand a good chance of dammaging the hard drive if you were to do it. Others may point out that you can find some incredibly strong magnets inside a hard drive, and that common refridgerator-type magnets are not powerful enough to penetrate the shell of a hard drive... blah blah blah... In the case of a Zune, the hard drive is teeny tiny. It has teeny tiny components. If a magnetic force acts strongly enough on any one of the teeny tiny parts, you'll begin to see some problems. So I'm saying that I doubt it will wipe your hard drive immediatly, but I'll bet that prolonged exposure is going to cause some physical dammage that may be worse than that.
My suggestion is to switch to a slightly smaller speaker so that you cut down on the problem by reducing the size and strength of the magnet. The other option is distance. Use a slightly larger case and mount the Zune and the speaker as far from each other as possible. May I suggest another solution? I would install the speaker and amplifier in an enclosure separate from your Zune. You can run a headphone cable between the two. I'd attach the amplifier to the side of your canoe and choose a smaller container (that floats) to carry the zune on your person.