Standard wood screws do work. With large heavy woofers, I'd use #8 wood screws long enough to penetrate at least ¾ of the way through the front baffle.
I prefer to use threaded inserts made for softwood (not hardwood). They come in a variety of lengths and diameters. They also come with flanges (as shown below) or without them. In my hands, these threaded inserts work much better than T-bolts or hurricane nuts. For a large woofer, I'd use ¼" diameter threaded bolts, but less than ¼" can work.
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This is a T-nut. They can work alright in soft wood like fir, pine or some plywood. With MDF, I avoid them like the plague. Getting the sharp prongs to actually penetrate all the way into MDF is difficult enough to make the effort fail.
If you're mounting a large woofer with 8 bolts, you really need a drill press to make sure all 8 holes are parallel. Without 8 parallel holes, the T-bolts go in ever so slightly crooked, making it impossible to drive all 8 bolts in.
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