When shopping for corner shelves that will hold speakers, remember to get a shelf that has a cut-out back corner. This provides a little bit of space for speaker wire to pass through. If you are using wireless speakers, then you don’t need this feature, obviously. Remember that placing your speakers in a corner tends to enhance the bass frequencies. Depending on the speakers involved, this may or may not be desirable effect.
Floating corner speaker shelves:
Floating corner speaker shelves pictured: Creative Connectors 6990367 Invisible Mount Corner Wooden Shelving
Since this kind of shelf tends to be used for small speakers, a boost of the bass frequencies may not be so bad. It all depends on the effect desired. If the idea is to fill a room with sound, with no particular concern when it comes to imaging, then placing the speakers high in corners can be quite effective.