all speakers used in surrounds in my opinion should have a low range of 25hz to 30 hz because there is no standard when the audio is mixed and information can be lost. for example Diana Krall her piano comes out the rear speakers
and her voice out the fronts,so if you don't have good speakers in the rear it will sound like an echo
and her voice out the fronts,so if you don't have good speakers in the rear it will sound like an echo