If I have Klipsh towers up front and a center channel. Can I put regular bookshelf speakers inthe back or must they be special surround speakers for the backl channels?
Any speaker will work. They do, however, make bipole and dipole speakers which are specifically made to be used as surround speakers. Those two speaker types typically have two sets of drivers which point in different directions to try to diffuse the sound.
For the best sonic results in a surround sound system, the ideal is to use speakers that all match in timbre(tone). That's why it is best to just use the same brand/type for all the speakers. The only exception would be a seperate powered subwoofer. You can use a different brand since it's only task is to produce omnidirectional low frequencies.
Any speaker will work but in order to insure the greatest integration of sound quality and transition of effects all speakers in a system should have similar voicing and tonethe easiest way to accomplish this is by using speakers of the same brand for all locations, but it is not absolutely necessary. Some serious home theater buffs recommend the same exact speakers for all locations they say this is the only way to assure proper voicing, but I think that is a little extreme myself
