Re: Speaker measurement tools
Yeah, I remember critiquing someone's measurements and how to self check with proven math, which he did up to a point, but still didn't get it right (mostly from following published instructions and others well intentioned help IMO); so this went on for several iterations without his measurements lining up close enough to the math until finally he and others claimed I was just 'jerking his chain' and that they were 'good enough' for box design. I agreed, but argued that until one can do repetitive accurate tests where using proven math makes it easy to confirm, then how can one be certain of other measurements where there's no easy way to check them? To his credit though, he kept at it and eventually he was able to find/correct all the errors in set-up, etc. to get ideal math accuracy to within a tiny fraction.
GM
Re: Speaker measurement tools
Quote:
Originally Posted by
Earl K
I believe you might be referring to sba2 .
- Sadly, that would make the following FR of his , need to be classified as "bunk" .
I guess I need to "de-bunk" that [802/511] measurement?LOL
As you might recall, I had discovered an anomaly in the impulse response that effects the resolution of the FR.
And not reported ?till now? While trying to solve that problem I found another. The mic?s phantom power supply / preamp (a Behringer tube mic100) was creating a significant amount of distortion. At least that?s what the audio analyser program indicated when I expanded a test beyond just the soundcard and included the cables, connectors, and finally the mic preamp itself into the in-out measuring loop.
After a lot of investigation I still don?t know the cause of the original problem, but a new soundcard installed on a different computer seems to work okay, so I?ll use that setup. For the distortion problem I replaced the Behringer with a Rolls MP13 mic preamp, which also seems to work okay. The analyser results are similar to those posted by bfish.
Soon as I find time I?ll re-measure and post here.
Re: Speaker measurement tools
Hi sba2 ,
Admitting ( once you found out ) that your measurements were contaminated by some glitch was absolutely the right thing to do . We all benefit by your honesty .
Anyways, I'd love to see some new plots of your 802s on ( your finless ) 511s .
- You represent one of only a couple known users with this unique combo ( & the only one I know with the ability to provide some measurements ).
- Any chance that you could do up a set polars in maybe 7.5 deg increments out to > 45 deg of axis / plotted by REW ?
<> cheers Earl K
Re: Speaker measurement tools
Quote:
Originally Posted by
sba2
...And not reported ‘till now… While trying to solve that problem I found another. The mic’s phantom power supply / preamp (a Behringer tube mic100) was creating a significant amount of distortion. At least that’s what the audio analyser program indicated when I expanded a test beyond just the soundcard and included the cables, connectors, and finally the mic preamp itself into the in-out measuring loop...
Yup, BTDT. Tha's why my current card has integral mic pre & phantom.
It does seem a bit tedious to test your test gear, but you'll never know it's right till you do. Sounds like you're well on the way to getting things whipped into shape.
FWIW, you can insert nearly anything in the test loop, though you'll be ahead to check one device at a time instead of the whole chain. For example, your test amp (or any amp FTM). I use a 1kHz sine to set up voltage levels. Say you ran 1V to amp input (or 0.7V if appropriate), and had the amp output loaded down with the appropriate power resistor to match the output tap. Run the amp gain up a bit to the output level you might use (I use 2.83V for 1M sweeps) and then add series R (variable's real handy there) to further load the output test point back to unity (1V). Hook that point to your card's line in, and the testware never knows it's there (unless the amp has problems). With RMAA you can retire a benchful of "old school" test gear and print out a detailed performance analysis in less time than it takes to hook it up.
You're gonna win, I just know it. :)
Re: Speaker measurement tools
Hi Earl,
It would be a pleasure to do polars and plot them in REW. I'm swamped with stuff for the next month or so, but I'll eventually find the time to make some measurements.
*********
Hi bfish,
Thanks for the additional info and the encouragement.
Re: Speaker measurement tools
After fixing some seemingly insurmountable problems with my soundcard and computer, I was finally able to get some decent measurements of an 802-8g on a 511b horn.
I don?t remember which details I?ve already posted, so once again?
The 802 was re-magnetized at GPA, and received a new 34647 diaphragm. The bug screen was removed, too. The 511 horn, in addition to being finless, is damped with self-adhesive roof flashing.
I made the latest measurements using both Holm and REW. With REW, 1/24 smoothing was about as high in detail as I could tolerate on the crowded plots?.so all of the REW and Holm plots that are posted here have 1/24 smoothing. I don?t have an SPL meter, so the SPL is only relative within a particular plot. The measurement distance was four feet.
I was also curious about seeing the 802 / 511 combo being run through a crossover. For that I used a Zilchlab designed model 19 network, and installed an 8 ohm dummy load at the crossover?s LF output. Before making the measurements, I used REW?s pink-noise generator and RTA screen to adjust the two Lpads for the flattest response. The Lpad closest to the driver was set at maximum, and the other Lpad, which controls the FR slope, was set at minimum. I noticed that the tradeoff here is with efficiency? in pursuing a flat FR, the output went down..
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Plot showing a corrected trace (top) and the earlier contaminated traces (below) --
http://img801.imageshack.us/img801/3...contami.th.png
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Plots created in both Holm and REW in order to cross-check the measurement systems --
http://img198.imageshack.us/img198/3...040holm.th.png
http://img512.imageshack.us/img512/7...2040rew.th.png
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Plot of the 802/511, 0 to 90 deg --
http://img811.imageshack.us/img811/3415/80290.th.png
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A less crowded plot , 0 to 40 deg --
http://img301.imageshack.us/img301/4374/80240.th.png
* * * * * * * * * * * * * * * * *
Same as above, with the traces separated --
http://img264.imageshack.us/img264/9...parated.th.png
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Re: Speaker measurement tools
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Plot of the 802/511 connected to the network, 0 to 90 deg --
http://img638.imageshack.us/img638/56/802net90.th.png
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A less crowded plot, 0 to 40 deg --
http://img220.imageshack.us/img220/4072/802net40.th.png
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Same as above with the traces separated --
http://img832.imageshack.us/img832/8...parated.th.png
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The crossover --
http://img547.imageshack.us/img547/8...model19.th.jpg
Re: Speaker measurement tools
WOW, Great Stuff sba2 !!!
Thank You, for providing such a comprehensive look at this horn/driver combo .
It's wonderful to have this as a resource :2thumbsup: ( hopefully you won't mind if I download your pics ? )
<> cheers EarlK
btw; what was your measuring distance ?
Re: Speaker measurement tools
Very cool stuff, I have 802's and am considering different horns so it is very relevant. Thanks for posting those results.
Getting closer to compiling what I think is going to get me started, first iteration will be a Behringer Electret mic and stand, a breakout box that will handle the mic phantom power and the usb interface, probably the M-audio product. Since I do most of my computer stuff on a laptop, I'm thinking a stand-alone PC just for measurement might be a good thing, I have a few. Choice for the PC might hinge on the sound card. What's a good soundcard for this kind of application?
