In Reply to: Re: diffraction issues again... posted by Wayne Parham on February 27, 2002 at 17:25:58:
Wayne,I realize the rat meter suks for accuracy, all I'm hoping for is that the readings/calibration is not so crappy that it will change a lot over short freq. ranges. I just hope to see trends, such as in the xover region...great from 1.6 k upward, but depressed below that, usually confirmed by ear.
Listening to the 4648's run high, they still sound nice on axis, and to each side of the couch, at 12 feet or so. I think the dual woof array does exibit less vertical dispersion also...where I had the mike at 1 meter may have been too close, and at a larger angle off axis than was appropiate. You are right, in room rat meter is not much help, and "proves very little".
But these crude measurements DO seem to identify why the higher crossed pair sounds a bit thin, what I was previously subjectively attributing to level differences and/or room position was shown in the depression from 500 to 1 kHz. I have four different 902-8b's that exhibit the 19 kHz. peaking...none of the other hf systems I've ever checked had that, so IN SOME some cases I think valid conclusions can be made from rat data...
I think crossing as high as possible to get the HF farther above the 500 horn cutoff (less distortion), and staying below 800 (less "nasties") puts me pretty well back where I was going before being distracted...to use about 2.5 or 2.2 mH 14 ga. coils, and cross somewhere around 750... I had briefly considered a WWTWW stacked array of 4648a-8 on the bottom, 511 horn in the middle, and a second 4648a-8 above...then I could be the comb filter king of the west...
And all I really wanted to do was confirm those recently built 4 Pi Pro xovers work as advertised. They do. Sand, Sand, Sand...
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