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The Parts Express  (PE # 300-794) has a built in rumble filter that cuts it off pretty fast below 20 Hz.  It also has an adjustable LP filter.  The above plot is an overlay of the amplifier voltage response with the adjustable cross-over set to minimum, middle and the maximum position.   This cross-over sucks!   I think they could really do a lot better job on this.  This particular sub will be used with a HT surround receiver which has it's own LP filter on it's sub output.   Using both the amplifiers LP filter and the receiver's it seems to work out pretty well but I really wish the amp had a 4th order filter.		Parameters of the DPL-12 in Free Air.		Parameters as measured in the box.   Qtc measures 0.71		Near field frequency response.