firing subs down?

I here some people say that aiming your subs down results in more bass is this true? thanks

not in and of itself .... if the positioning happens to put the sub in a pressure node, then yea ........ it will increase your bass output

pressure node?

yes ... inside the listening enviroment, there are high and low pressure nodes. When you put a bass speaker in a high pressure node, it will play louder ..... in low pressure node, it will be anemic. This is why some bass systems have seemingly very little output - even though the size of the subs and power of the amp are more than sufficient.

For a better description, try looking up the Kuntz tube experiment (from physics).