I dont think you'll notice a difference. With the 3/4", the walls of the box pretty much won't flex at all. The 1/2" might have a little give in it but honestly I'm not sure. I would bet almost anything that you won't notice a difference in 1/2" to 3/4". Doubling up the baffle (mounting surface) would be a good idea though just to make sure that the sub's mounting screws hold into the wood well.
Will
Will
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