my first caller was a home made one.i used a portable tape player,not a walkman they didn't have those in those days.it was a bigger one that had a little more volume then a walkman.put a 4 inch indoor/outdoor radio shack speaker with 25 foot of wire.called in many fox with that set up,never called any coyote with it becouse there wasn't any coyotes in ny during the early 70's.my point is,any thing that plays clean crisp sound will work as a call box.and you don't realy need a box with super high volume.i am a firm believer that less is better.