difussor's

Diffusors (at least 1D diffusors) will not deaden the sound in the room, but can clear up and stabilize imaging while leaving liveliness in. If you have dipoles, then diffusors behind the speakers is probably a good idea. Otherwise, they usually work best behind or to the sides (but should be at least 4 or 5 feet away from your listening seat).

If you don’t mind a little (actually very little) work, and are in the USA near some lumber or big box hardware stores, you might want to try my DIY 2D diffusor design (actually designed via computer simulations rather than math formula or cut’n’try). See: http://www.diyaudio.com/forums/everything-else/269366-making-easy-diy-depot-sound-diffuser-panels-st...

If you are in a metric country (and don’t mind a little more woodwork), take a look at Tim Perry’s "Lean Fusers" at: http://arqen.com/sound-diffusers/

While checking back here, I noticed an error in my post above -- my DIY diffusor is a 1D diffusor,  Which is probably the kind you want, 2D diffusors tend to diffuse too much energy toward to floor and ceiling, so that much of it dissipates before it reflects around off multiple surfaces to reach your ears; not a lot different effect than just using an absorber, IMO.

Diffusers on the front wall would still be for "live front".  Diffusers don't deaden sound, they just make it more diffuse (break up the reflection to cause less interference with the direct arriving wave at the listener).  

Front-firing speakers (except for maybe horns) don't radiate only toward the front.  The *desired* wave is only forward, but there is still plenty going toward the sides and to their back, just aim a speaker away from you and see how loud it still sounds!  The higher frequencies are less toward the back, though, and unfortunately the lower frequencies are much less easily diffused (or even absorbed, for that matter) than the highs.

But a dipole speaker (most ESLs, Magnepans, Apogees, Linkwitz, etc) radiate the same toward their back as toward their front.  It is a good idea to deal with the back wave, either break it up with diffusers (if you want to keep the room sound lively) or absorb it (if you're ok with some deadening, or want an easier route than constructing diffusers).