John, a perfect example of what Steve said would be to compare the results of 2 subs recently tested by Ikka. Look at the response graph of the SVS PB13-Ultra tuned to 15hz,
http://www.hometheatershack.com/foru...-tune-new.html
and compare that to the response graph of the SVS PB13-Ultra sealed.
http://www.hometheatershack.com/foru...ealed-new.html