Ah, a new way to destroy books and have fun at the same time. Some bright thing has come up with an idea of camouflaging shelf speakers as books by cutting up a few hard covers. I used to use a hollowed out street directory to hide spare keys in a previous household but like this idea too. Admittedly, it probably muffles the sound a little too much I’d guess; you’d probably want to use some sort of cloth (with pictures of book spines) across the bit where the sound comes out. Rather than cutting up books, it might be better to stick together some slipcases instead, living the the books themselves intact.