If your wedding or party is being held in a unique facility with specific acoustic issues (multiple rooms, indoor/outdoors, echo issue, broken up ceiling surface, in a tent, etc.) then you need to educate yourself. Normal placement of your DJ's speakers ? on speaker stands, may not be the correct thing to do for your given room layout. Your professional disc jockey should be able to offer you knowledgeable acoustic solutions to your needs.
For example, if your DJ is located at the corner of the dance floor v. located along one side of the dance floor ? they may suggest to "point-source" their speakers. This would place all speakers at the corner of the dance floor and they would fan the entire room.
With rooms with known acoustical echoes (hard surfaces, such as marble), they might suggest using remote broadcast speakers and using a time delay on one set of speakers. They might suggest placing their speakers on the ground pointing upward at a 45 degree angle v. on stands.
The real problem you will have is if your DJ sets up their system the same way regardless of the acoustical situation. If they do not know the difference between near-field and far-field speakers (far-field speakers throw their sound further and work well for larger rooms or outdoor areas) they you need to find a qualified professional DJ that does.
Why such a concern? If you want everyone to hear the best man's toast or introductions and if you want something better than "boom box" sound at your wedding, then it becomes imperative that you educate yourself prior to hiring a DJ just because they are the cheapest quote that you've received. Quality comes at a cost.
Rob Alberti
After Hours DJ Service, New England Area DJ
http://www.afterhoursdj.net