I guess I sound like a "doubting thomas", but the delay distance "should" be greater than the actual distance, in order to account for the physical path length of the horn.In every case that I can remember, the delay time was much, much longer than the actual distance between the mic and the cabinet.
Art, glad to hear you are surviving being a "welter".....funny, thx !
If I may re-quote what I wrote in reply #12 ..."the delay finder readings tie exactly! with expectations...
But having the same arrival time is RELATIVE, not absolute.
Back to the question you raised in the first post:"I'd be interested if people think this testing methodology holds water...."It seems OK, but the Lab Sub minimum impedance is almost the the same as it's DCR, a pair with parallel drivers is only 2.145 ohms, which is almost a 6 dB sensitivity gain at 2.7 volt compared to a "one watt" voltage.When that is taken into account the sensitivity no longer looks freakishly high."Freakishly High", sounds like a good band name..
I'm going off into hypothesis world like I always do, and am left wondering if a 2.83v bandpassed rms measured pink signal that I use has more energy than whatever "2.83v signal" is normally used???
1)In a 4 bank, I'd call a single lab with drivers in parallel a 5.5 ohm nominal...not dipping below 3 ohms. I feel pretty solid here..So I know this makes the numbers I posted look even more freakish ....2)I'm going off into hypothesis world like I always do, and am left wondering if a 2.83v bandpassed rms measured pink signal that I use has more energy than whatever "2.83v signal" is normally used???(But one weakness in that theory is the OS sensitivity I measured tied right to published spec.)
Here is an interesting experiment.
Mark,1) Silas Pradetto did impedance testing with his Labs, the impedance minima is near the DCR. Unfortunately, his reports were lost in the transition from the old "LAB" to "Pro Sound Web". A "nominal" impedance is just that, something of an average, but for sensitivity tests the impedance minima should be used. Wayne Parnham's PI subs, basically a larger Lab, also read near the Lab 12 DCR, and Hornresp simulations on nearly every FLH and TH I have designed all have impedance minima near the DCR of whatever driver used.2)Unless things have changed since I last looked, Jeff does not publish a measured response for the Orbit Shifter, making the sensitivity a bit questionable, though it does appear to be an average of the pass band he references.I have never been able to get what I consider a reliable "RMS" voltage using pink noise (probably due to cheap meters..), so have always used sine waves at various frequencies, setting the voltage ( 1.41V for 2 ohm, 2V for 4 ohm, 2.83 for 8 ohm etc.), at 60 Hz, where the meter should be most accurate. I do my testing at 2 meters, and subtract 6 dB for the inverse distance rule.I also like to test at the excursion minima, which usually happens to be the impedance minima, the speaker draws the most power at the frequency where forced air cooling is the least. After the sine wave tests (which also can be used to measure distortion) I then match them to the pink noise tests, so an accurate reference 1W/1M SPL is known. Art
1)I took a quick 1 Lab dats below just now, because all my old data is on a retired PC. You'll see the minima isn't that far from DCR. 2)Also took a dats of an OS. I figure you know this site, but in case not, data-bass makes the best sub measurements I've found http://www.data-bass.com/data?page=system&id=119&mset=1313)And yeah, that damn pink voltage can sure bounce around, can't it? Even when I use a minute or so averaging, still end up with average to average variations up to 0.20 v. For sensitivity, I just normalize whatever average shows up to 2.83v, and also normalize whatever SPL LEQ that was measured over the same period..4)Oh, a bit of a swerve if I may...how do you measure distortion? I've been trying with REW. Results seem reasonable, but I'd like a way to find some confirmation...thx.
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