Valid Efficiency Test?

I'd like to measure the efficiency effects of adding passive high-pass filters into my system. I can measure SPLs (Radio Shack meter) of mains at listening seat with and without the filters (all with subwoofer off; volume knob stationary). I was thinking of using white noise signal (track from ACI Subwoofer Test CD). Would this be a valid test?
Are the filters going before or after the amps? If before(like they should): It won't make any difference to the speaker's efficiency measurement, because that's based on 1W(or 2.83v) output from the amp. You don't measure from the speaker to your listening position, but- rather one meter from the speaker. You'll need to have a way to measure exactly 1W of output power from the amp. Usually, the measurements for listed speaker efficiency ratings are done in an anechoic chamber, with either white noise, or at a certain given freq.(IE: 500Hz, 1kHz, etc). That's what would be considered a "valid" efficiency test yielding a "so many db/1W/1M @ so many Hz" result. Of course for your purposes: You could put the mic wherever you want, set your volume and measure the SPL. Then install the filters and repeat, noting the DB drop(which there will be, if you don't change anything else).
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Doh! That's true. I forgot about the insertion loss. Filters are on input to amp (RCA). This is not the way to go about doing it. Never mind. Dumb idea. Thanks guys.