Originally Posted by Jay1
I've never done an active setup, but I imagine with a CD you would want to put a resistor in parallel with the +/- terminals in order to squash the impedance peaks at FS. Usually tweeters will "squak" at you if you play them into uncompensated impedance peaks. Something like a 15 ohm resistor should have a minimal effect on everything else.
Is this really necessary with an active crossover? I remember reading that it wasn't, but I don't remember why. I use compression drivers in an active setup and there's no "squak" to be heard.
I'll second what augerpro said about getting good data. Garbage in = garbage out. Like mtg90, I find I get the best results outdoors, but if you can't do that gated indoor measurements will suffice for the xo. When I do this I clear the room out as much as I can, get the speaker on a stand to get the design axis halfway between the floor and the ceiling, and I've got several batts of bonded logic I like to throw on the floor so it's about 2' deep. Also, having the speaker and mic at a diagonal across the longest dimension of the room will give you the greatest distance to the side walls. With an 8' ceiling I get about 3ms of clean impulse. This short gate will give the appearance of a high pass much higher than the speaker actually rolls off, and has the effect of smoothing the data <1khz.
I'll also second what augerpro said about using dual channel measurements, though I use REW which is a swept-sine measurement and not MLS. This makes it easy to look at the phase relationship of the drivers and determine exact delays. The reverse null method works with LR type crossovers but I like to see good phase tracking on either side of the xo, and I can calculate the delay by the difference in phase angle at the xo. For a beginner, maybe the reverse null method is best
Another nice this about REW is the eq section. It has most of what you need to "simulate" the filters you will be using. ARTA is good for designing crossovers, because it has an overlay feature that will overlay various xo filters (LR, BW, etc) at whatever level and frequency you choose.