sound attenuation with 4" brick, 1" air gap, 2" Safe'n'Sound, 4" brick

I was initially planning to isolate my home theater with a clay brick wall with an air gap of 6" between. Later realized that having a 6" space would not be practical as it will reduce the room space quite a lot. However i still need a pretty good isolation. My plan is to reduce the gap to 3" and put Roxul's Safe'n'Sound 2" between the walls which will result in a 1" air gap. Appreciate if some one can help me in finding sound attenuation at low frequencies for such a setup.