You should be OK as long as are not putting the speakers on shelves inside of a bookcase, because then you would be putting a box inside a box. Up front realize that the speakers can be made to sound very good, but not their very best.
Sealed speakers or front ported speakers will work better than rear ported speakers, though some rear ported speakers will surprise you with how good they can sound on shelves Rega RS 1 .
Placing speakers vertically, as opposed to on their sides, works better unless the speakers are designed to also work on their sides, like the Ascend Acoustic Sierra 1 Monitors .
Speakers that I have owned that worked very well on shelves: Ascend Acoustic Sierra 1, Rega Ara (now the RS1), NHT SB2 (now the Classic 3). Speakers that did not work very well on shelves: Totem Mites, Energy RC10, Wharfedale Diamond 9.1 (now the 10.1), B&W 302, EPOS ELS3.
Rich
Sealed speakers or front ported speakers will work better than rear ported speakers, though some rear ported speakers will surprise you with how good they can sound on shelves Rega RS 1 .
Placing speakers vertically, as opposed to on their sides, works better unless the speakers are designed to also work on their sides, like the Ascend Acoustic Sierra 1 Monitors .
Speakers that I have owned that worked very well on shelves: Ascend Acoustic Sierra 1, Rega Ara (now the RS1), NHT SB2 (now the Classic 3). Speakers that did not work very well on shelves: Totem Mites, Energy RC10, Wharfedale Diamond 9.1 (now the 10.1), B&W 302, EPOS ELS3.
Rich