what does the sms-1 do?

I purchased the lmf1plus sub. I don 't understand what the sms1 is used for? is it constant usage? as far as the lmf1+ i find it an excelent sub. It makes my windows raddle. Now I have to find a fix for that. the responce is excelent. I dont think you can find a better sub for that price. Just like any quality sub though, 1 can fill me room; well let me say, OVER fill my room, but 2 would be better just to get the bass spread out more evenly.