Speaker Magnets - How Are They Attached?

[spinner 0]

A short while ago I bought a used pair of Soundlab powered cabinets, via Ebay, to use as a PA for speeches in marquees and larger rooms.

 

I tested them only briefly when they arrived and they seemed OK.

 

Yesterday I tried them again, this time more thoroughly and one cabinet sounded louder than the other.

When I opened it up to have a look I saw that the magnet for the main driver had slipped right down so that it's edge was resting on the floor of the cabinet.

 

I moved it back into position and it seemed to be fixed firmly. I have not tested it since but I wonder if it might come off again with the vibration. Should there not be some other method of affixing the magnet than just it's own magnetism?