How can i get my 2 12" mtx terminators to hit harder?

I bought the package deal with the amp. it seemed to hit hard then recently it doesn't anymore. is there a way to make it hit harder? i have the b boost on the highest and the gain is turned up. It is really cold where i live and i park outside. Could that be causing a problem sense they are cold? if someone knows what i can do to get them to hit please help