looking to build a sealed subwoofer box that will get my sub down to 20 hz .. i have the HF 15 http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=295-468 which is rated to 18 hz. so im looking to build a CUBED, SEALED box that will get down to around 20 or so hz... will have a 1000 watt amp on it.. max on the speaker is 800 so it should be more than enough