Jeff Permanian wrote on Mon, 24 January 2011 09:10 |
Art Welter wrote on Fri, 21 January 2011 18:29 | The SRX subs are not measured in full space, neither were Phil's measurements of either sub. His measurements of the JBL are within 2 or 3 dB of the JBL chart, considering his microphones are not calibrated or big buck, that is pretty close.
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Art Welter wrote on Thu, 20 January 2011 14:20 | I have attempted to calibrate my Smaart readings, but am not sure if they are absolutly on. I have not attempted to calibrate them with the RTA 420 microphone I was using in the above test. I have written several times that I can’t get my 3 meters to agree at more than one frequency..
Art Welter
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Forgive me if I question the absolute level of your measurements and your correlated sensitivities.
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Jeff,
You are forgiven, and I’ll be glad to answer any of your questions
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I have not claimed any absolute levels, though I have plenty of posts saying what my meters read in various situations.
Correlated sensitivities are fairly simple. Measure two speakers under the same conditions, and relative levels are established. If the measurements look like the specs, good!
If they don’t, either the speaker is different due to production tolerances, the measurement positions relative to boundaries was different, or the measuring tools don’t agree.
I compared one of my front loaded 2 x12” Lab subs, nominally a 3 ohm load, to a JBL SRX 728, using the same drive signal, pink noise with a 25 and 125 BW filter, the undriven sub remained by the other sub, and was shorted out. Speaker cords were swapped into the same amp channel, no levels or settings changed.
As you can see, the JBL looks like it’s published specs, so the correlation is good, other than the RTA 420 microphone I used for the test reads a couple dB low at 30 Hz, and the filter reduces the LF output a bit more.
I don’t think you would suggest that a dual Lab 12 is any more than 92 dB , one watt one meter, or the JBL is louder than it’s published specification. This answers the half space or full space question that has been raised before, the SRX line is measured in half space.
The SRX 718 is basically half a 728, so three dB less sensitive, rated at 95, rather than 98 dB.
Phil Lewandowski’s measurements of his Growler and 718 come out remarkably similar to each other, which implies the Growler is the about the same sensitivity as the JBL SRX 718 in the 45-100 range.
The 2007 Prosound Shootout also shows the Growler to be about 95 dB average sensitivity 45 to 100 Hz.
A few days ago, I was surprised to find my “quick and dirty” test position six feet outside my shop door added 4 dB in the octave around 40 Hz compared to the position I did the above test at, about 40 feet from two buildings.
As Ivan Beaver wrote: “getting accurate measurements is not as easy as it may seem”.
Those measurements, and the Orbit Shifter’s 2 dB (or possibly 8 dB depending on voltage applied) discrepancy between your graph and specified sensitivity are why I asked you for distance from microphone to speaker, microphone calibration, and distance to any walls.
Art Welter