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Post by chrisbee on Apr 5, 2007 11:45:57 GMT -7
Here we have a direct comparison between three SPL meters in REW. Red is new RS meter with new rs cal file. C-weighting checked. Mismatch! Green is new RS meter with old rs cal file. C-weighting checked.Blue is old RS meter with old rs cal file. C-weighting checkedViolet is Galaxy 140 with galaxy cal file C-weighting unchecked.
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Post by htnut on Apr 5, 2007 15:27:10 GMT -7
What is a new RS meter? I have a 33-2050.
And it goes to show that most things done to prove a point are meaments. That is measurement with the sure taken out.
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Post by chrisbee on Apr 6, 2007 5:31:37 GMT -7
The newer 33-4050 RS SPL meter is about 2/3 the size of the older boxy meter and has a softer, more organic look.
There is some confusion over which REW cal file suits it best.
Attempts on HT Shack to pin down a changeover date to the correct cal file were fairly successful though with some doubt as to exact date.
The older meter is not inferior. Since it has an almost identical response to the new one when used with the oldrs analogue cal file.
My own meters are at least 12 years apart in age but are virtually indistinguishable in REW. See the blue and green response curves in the graph above.
The Galaxy 140 has been carefully compared with a recently and professionally calibrated ECM8000. The Shack's brucek produced the cal file from the comparison curves.
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Post by htnut on Apr 6, 2007 9:03:15 GMT -7
Too bad Thomas couldn't measure with his calibrated setup. I would like to know if I am measuring "hot" when I'm "not" using the cal file for the RS. If your purple is really more correct then I woiuld adjust my RS cal numbers.
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Post by ThomasW on Apr 6, 2007 10:05:53 GMT -7
I've never owned a RS meter (or any other brand) so I don't have any hands on experience with them.
All these devices (SPL meters and the ECM8000) start dying below 30-40Hz, so yes use the appropriate .cal file for your device.
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Post by htnut on Apr 6, 2007 10:13:16 GMT -7
Thomas,
I do use the cal file for my Rat Shack meter. What concerns me is that Chris is getting much higher "adjusted" readings using the Rat Shack with cal than he is using the Galaxy 140 with Cal. If I take the Galaxy as a baseline, I would then have to say that I am getting way too optimistic readings using the cal file for the Rat Shack as it stands. It would be easy to redo my cal file using the Galaxy purple line as a baseline.
It appears that the truth of the cal file for the Rat Shack may lie between the red and blue/green.
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Post by ThomasW on Apr 6, 2007 10:22:51 GMT -7
Given it's cost I'm sure the Galaxy is more accurate than the RS meter.
That said variations in temperature, barametric pressure, altitude, etc., etc, effect how these devices measure.
We used to routinely ship our 4133 back and forth between Denver and San Jose for test sessions. Problem was each flight changed the measurements. It's ~$300 for a real calibration, as opposed to relatively simple $40 comparison Kim Girardin does.
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Post by htnut on Apr 6, 2007 12:08:41 GMT -7
This is making my head hurt . I know that there are variables in the measurements. What Chris is showing is that in the same room with the same atmosphere etc. he is getting a very different meament with the Rat Shack as compared to the Galaxy. The shape of the curves match very well. It is the magnitude that is off. I think I will not add so much for Cal to the Rat Shack meter and try to get closer to the purple line of the Galaxy next time I fool around with my IB. Wife has not been out of the house for quite some time when I am around so I cannot fool with it. She would come unglued if she found out that I shake the windows so hard in their frames that there is relative movement of the window framing with the house framing. And that at only 90 dB. Yes I have found the resonant frequency of our family room window assembly. 15 hz.
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Post by chrisbee on Apr 6, 2007 12:43:37 GMT -7
Windows seem remarkably tolerant to sonic abuse. When I had a demo of a commercial sub in a very large showroom the shop windows right beside me looked like they were bowing 1" in and out! It was terrifying seeing people walking past so close to the glass! I'll chase them upon the Shack about the observable differences between these meters. Tests were only seconds apart and matching cal files loaded. The meters went into the same tripod adaptor plate and were orientated identically. I believe the cal files for the RS meters are limited to 20Hz. The Galaxy to 5Hz.
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Post by htnut on Apr 6, 2007 15:23:47 GMT -7
This is not the glass bowing. I was able to do that with a pair of Altec Voice of the Theaters in a building where each pane of glass was 8 feet wide and 16 feet tall. A Frank Lloyd Wright design in the woods near Cleveland.
This is the actual framework of the window. It is plastic I think. The whole window assembly moves in the wall. Makes creaking sounds like plastic rubbing on plastic. I may have to oil it. ;D
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Post by chrisbee on Apr 7, 2007 0:14:40 GMT -7
Good grief! The things we suffer for our hobby. ;D
Sounds like a job for a thick bead of flexible silicone sealer.
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Post by htnut on Apr 7, 2007 6:54:37 GMT -7
My lovely wife would shoot me for sure if there was a thick bead of anything on that window. I think HT and Wife are like oil and water. Don't mix.
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