I believe you have the right idea, that is the only reason I can see to have one. To eliminate the frequencies you can't hear. One thing to consider, which is why I believe not all manufacturers use them, is that you can't HEAR freq. below about 20Hz but you can still FEEL them. Assuming the sub can play that low of course, which many good subs can. My 2 cents.
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Brad W.
1998 Silver Frost SE brantleyiii@earthlink.net photos.yahoo.com/brantleyiii ------------------
"Good leaders are scarce, so I'm following myself."
