Just got a new 12" velodyne sub, and need to know how to calibrate it for a flat response, hopefully. Will i need to buy a sound meter?also, does increasing the db range of speakers using the channel level setup (using a reciever) distort the speaker at higher volume, or is it there to make the fronts louder than the sub etc....?

Depends on which one you bought.

http://cgi.*********/RadioShack-Digital-Sound-Level-Meter-33-2055-NIB_W0QQitemZ190114290778QQihZ009QQcategoryZ25423QQssPageNam eZWDVWQQrdZ1QQcmdZViewItem#ebayphotohosting

will the aboe spl meter do the trick for speaker/sub calibration?

The only way you'll get a flat response with your sub is by:

1) Reading this first: http://www.ethanwiner.com/acoustics.html

2) Reading the subwoofer related articles here: http://www.avsforum.com/avs-vb/showthread.php?t=824554

3) Using a software like Room EQ Wizard to run frequency sweeps to graph the response of the subwoofer in your room and move the sub to a different location in your room with each sweep to find the spot that gives the flattest response. You

4) Getting some acoustic treatments for your room (aka bass traps) to address any problem areas.

5) If after having done all that and you still have some big peaks, get a unit like the Behringer Feedback Destroyer to EQ the sub and reduce some of the peaks in your room.