From a reply on FB
I built a speaker for a swimming pool. It was a large can of steel with an audio transformer mounted inside. The ‘I’ laminations were removed so the ‘E’ laminations could be very close to the end. I drove it with a 2N3055 on a heatsink. The secondary winding must have DC flowing to magnetize the laminations. I used a car battery for power.
I soldered the lid back on the can. I put clear silicone sealant around the lid where the two wires went through. It worked okay for awhile but the water leaked in and the steel rusted.
