I use cabinet grade birch veneer ply.

If doing a living room speaker, as opposed to commercial, or PA, I cover the edges with birch tape. To do this, I sand the cut ply edge and paint two coats of carpenters glue on the edge, as the first coats really soaks in. If any drips on the side to be stained, I wipe it away carefully with a wet rag. Otherwise, stain will not penetrate and a light spot will show there.

I thumbtack the birch tape to an old scrap of ply, and paint that with one coat of carpenters glue.

After all dry, I place the birch tape in position, and using an old household iron, set to a cotton/wool setting, I IRON on the birch tape, following with a dry cloth to hold it while it cools for just a second. This attaches the tape quickly and easily with no drips or runs of glue, as the glue is already dry.

Now, trim the excess with a utility knife. Hit it lightly with sandpaper and you are done, a beautiful edge.

More than 25 years of using this method has proven it. And it stays on!!! I have some spkrs in the house now more than 20 years old, the edges are still just fine.

And I use 7 to 10 coats of tung oil, hand rubbed, as per a post previously on here by another fellow, who described a method almost exactly as I use.

For PA and MI spkrs, I cover with carpet using contact cement, or with transportation vinyl.

While I will sometimes use MDF with veneer for indoor spkrs, MDF will not hold up for road use.