SPL Meter Correction Tables - Page 4 - AVS Forum
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post #91 of 212 Old 05-26-2006, 12:25 PM
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Carlos, you've provided a intriguing criticism (although in my experience the RS SPL meters don't exhibit the variance that you suggest). If they have power compression problems themselves, then maybe they're inappropriate for power compression measurements. I'd be interested, though, to know what mics the guys doing those measurements use, and why the ones that use RS meters don't all show the same results, since the meter should go into compression before the sub?

In any event, what's the alternative? Spend four or more times the amount on better measuring equipment? Or just don't do any measuring?

I find both of those alternatives unacceptable. Do you have another?


BTW, please provide a link to the mic on the audioXpress site. I didn't see one.

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post #92 of 212 Old 05-26-2006, 02:05 PM
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Quote:


This whole thread is frightening.

No doubt to a professional in the business such as yourself, it is so. For those of us trying to get the best audio systems for as little money as possible, not so much. The suggestion to invest $500 in a measurement device for a subwoofer, so we can tame a few room responses is not going to be readily embraced.

I'm surprised that you've experienced such a disparity between these cheap meters. When Sonnie had his ECM8000 microphone professionally calibrated (I suspect you'll not be giving the thumbs up to this mic either - doh), we decided it would be interesting to use it as a standard and try and create some calibration files for the three different cheapo Radio Shack meters on the market.

We had already created a file for the original analog meter, but thought we should attempt the newer analog meter and its digital partner since there had been some discussion whether the newer models had a better response.

As we've readily admitted and as I'm sure you can obviously attest, the results obtained from measurement data (against a standard) are dubious at best. But either way, we felt that the final proof would be in the comparison of frequency response data using each meter in question utilizing the popular Room EQ Wizard program.

Granted, when conducting any experiment, a sample of four is questionable, but telling none the less. Sonnie tested two new analog meters and two new digital meters. We created the calibration files for them. The meters were suprisingly close. Maybe we got lucky.

Below is the frequency response of the professionally calibrated ECM8000 mic/meter against the two analog meters and the two digital meters using the newly created calibration files from Sonnie site. Sonnie used his home theater as the test bed.

They appear fairly close to me and good enough for home use. There are differences, but every measurement reveals a new set of differences. The point being that in a home environment even the smallest positional difference or speaker movement will result in some reponse change. This is evidenced by the anomolies that kept showing up at 22Hz, where each measurement revealed a different response at that frequency. Anyway, you can see that these five responses are within a few dB. That's good enough to set up filters in a parametric equalizer when you have a room resonance that is causing a peak in your response of 20dB at 50 Hz. It sure works for me.



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post #93 of 212 Old 05-26-2006, 03:29 PM
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Quote:
Originally Posted by DMF View Post

BTW, please provide a link to the mic on the audioXpress site. I didn't see one.

I think he is referring to the Mitey Mike II Testing Microphone at $193.95 which has been calibrated for use with one of the KD-4 series preamps (from 128.95 to 269.95 depending on whether you want a kit or prebuilt unit and depending on whether you want one or two channels, which one channel would be all you would need)... however, none of the preamps to which the mic is calibrated are available. The mic might work with another lesser expensive preamp... don't know. The mic itself is rated ± 2 dB, 10kHz-20kHz.



I'm not so sure how this could be all that much better (if any better at all) than the 50 dollar Behringer ECM8000 measurement mic that is ± 2 dB, 18kHz-46kHz straight out of the box. Of course you'll need a $40 preamp and if you wanna get really accurate all the way down to 10hz (where we can't even adjust - not with the BFD anyway)... you can pay 40 more bucks and have it calibrated against one of those $2,000 mic setups. $130 total.

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post #94 of 212 Old 05-26-2006, 04:21 PM
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Bruce,

Your data makes sense and looks good. I agree that things are much better once you individually calibrate each sound level meter.

My impression from reading the messages on this thread is that people are making calibration tables and telling everyone "Here, this is the calibration data for this model of SPL meter". That is what is so terrifying. The models simply vary too much from one to the other. Not just in response, but in level. I looked up the specs at Radio Snack and they only say +-3dB from 50Hz to something in the several k range. That means that one meter could be off by as much as 6dB in comparison to another meter....in their "mid-band". Outside of this range, that difference will increase rapidly. Incedentally, even the R/S lit says the response drops like a rock at very high frequencies.

Acoustical Measurements is an area of expertise of mine...and the readers here need some help. Here we go:

MICROPHONE ITSELF:
BTW, for everyone out there. In case you did not know this. The "GOOD", low cost electric condesner mic is the Panasonic WM-61A available for less then $2.00 at DigiKey. DON'T BUY ANOTHER MIC CAPSULE. Many people don't know that companies such as Earthworks simply buy this mic, dress it up and add some good electronics around it, and sill them for $2,000.00 . Quite a nice mark-up. Just put the mic itself in a small diameter brass or AL tube from the local hobby store. Use the default mic circuit that Panasonic recommends, and you have yourself a pretty decent microphone . It is so cheap and easy to do, I always encourage people to go ahead a make several of them at a time. Many of the $100-$250 Measurement mics out their are exacly this.

ELECTRONICS:
There are several small companies (people) that make inexpensive test and measurement gear. One of them is Here .

This software is $150.00 and works with a sound card. Do any of you guys have sound cards in your PC

Seriously, be careful. When talking to this guy, or any other similar outfit, ask them what cards they recommend. Honestly, it may well be worth it to buy the card they recommend.

SO THERE YOU HAVE IT. A reasonable OPTION FOR AROUND $200.00 (WITH misc. hardware and electronics for the microphone). This set-up will measure LOTS of different things with REASONABLE accuracy.

BTW, I am not recomending the etfacoustic outfit over anything else. I have no experience with them. I do know that there are a few outfits like them out there. Just do an internet search like "Audio Measurement System PC Low Cost" and things will pop up.

Also, there are many options for low cost dedicated hardware items. Such as the Clio Lite System available here. This particular one is very good and is $650.00. Other can be found in the several hundred dollar range.

Anyhow, I hope this helps.

Carlos

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post #95 of 212 Old 05-26-2006, 04:33 PM
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Sonnie,

EXACTLY!

Your response showed up before my longer one. Yes, the Mitey Mike is one of the mics I am reffering to when I said there are many mics in the $150 to $200.00 range that are exacly this. Several of the companies that make inexpensive acoustic test and measurement gear offer something very similar. In all fairness to the two guys who designed the Mitey Mike (I know them both), it is better than what the average person will put together with my simple directions above.

Anyhow I got to GO!

Carlos

P.S. How come you guys haven't ordered my drivers yet?

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post #96 of 212 Old 05-26-2006, 08:27 PM
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Those drivers look impressive. Seem to be a tad on the expensive side though in relation to what else is available. You designed and built those yourself?


Quote:
Originally Posted by CBeltran View Post

My impression from reading the messages on this thread is that people are making calibration tables and telling everyone "Here, this is the calibration data for this model of SPL meter". That is what is so terrifying. The models simply vary too much from one to the other.

Those 4 meters tested in that chart are from different geographical locations intentionally. From about 29hz on up to 150hz they are +/-1.5db (maybe one spot on one meter is 2db) of each other and the reference mic. It's hard for me to believe that we would find many that would be as much as 6db difference. Chances are unlikely based on this test anyway. Maybe several years ago the consistency might not have been that good. Look around at the various companies that are now putting their label on these units... they are all the same meter, just different names. They rate the response +/-2db from 32hz - 10khz... which would definitely be consistent with what I've measured and tested with the four above.



Quote:
Originally Posted by CBeltran View Post

Not just in response, but in level. I looked up the specs at Radio Snack and they only say +-3dB from 50Hz to something in the several k range.

The level is not gonna make that much difference. We are mainly looking at response. If the level is off it will be uniform throughout the response.

I think you may have gotten some outdated info on the RS meter OR maybe RS just hasn't updated their info... or they are just being extra precautious... again... these are the same meters others are selling labeled with a different name and they have obviously improved them.

Not only that... I have shown earlier on about 3 different occasions in this thread... comparisons between another member test and one of my older test. Each RS meter from different parts of the world. Each compared against different types of calibrated mics... his mic much more expensive than mine. We were within 1.5db of each other from 16hz to 100hz which would be a very reasonable difference from one RS meter mic to the next based on recent tests.

I know bruce stated maybe we were lucky.... (I would say it sarcastically)... but seriously, I find it hard to believe based on all these tests that it's just coincidence that we happened on 6 different meters from different directions, dates of manufacturer, tested with different calibrated mics.... that they are as off as you suggest. The most recent test we have done just don't suggest it.



Quote:
Originally Posted by CBeltran View Post

Incedentally, even the R/S lit says the response drops like a rock at very high frequencies.

We don't care about high frequecies. We are not doing full range measurements. Look at the correction values that are posted here. We have only provided 10hz to about 100hz. Some folks may indeed be using it for whatever... but we did the tests strictly for use with the BFD as it is being used for its parametric eq on subs.... not full range speakers.



Quote:
Originally Posted by CBeltran View Post

MICROPHONE ITSELF:
BTW, for everyone out there. In case you did not know this. The "GOOD", low cost electric condesner mic is the Panasonic WM-61A available for less then $2.00 at DigiKey. DON'T BUY ANOTHER MIC CAPSULE. Many people don't know that companies such as Earthworks simply buy this mic, dress it up and add some good electronics around it, and sill them for $2,000.00 . Quite a nice mark-up. Just put the mic itself in a small diameter brass or AL tube from the local hobby store. Use the default mic circuit that Panasonic recommends, and you have yourself a pretty decent microphone . It is so cheap and easy to do, I always encourage people to go ahead a make several of them at a time. Many of the $100-$250 Measurement mics out their are exacly this.

This may some good info.... if people are inclined to build a mic.

Could the capsule be a replacement for the RS Meter capsule?

Remember, we still have to have the SPL meter.



Quote:
Originally Posted by CBeltran View Post

SO THERE YOU HAVE IT. A reasonable OPTION FOR AROUND $200.00 (WITH misc. hardware and electronics for the microphone). This set-up will measure LOTS of different things with REASONABLE accuracy.

Not really reasonable. Again... we still have to have an SPL meter. Now you are back to $250. Most are gonna be satisfied with the $40-50 for the RS Meter.

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post #97 of 212 Old 05-30-2006, 08:45 AM
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I think I have misunderstood something here, and I have also been misunderstood.

I thought the measurments posted by Bruce were using individual calibration files. I am a bit confused still, but after re-reading, it appears he used some "standard" calibration files.

I have also noticed that a few of the low cost SPL meters seem to look the same. Most likely they are all coming from one manufacturing source and it is possible that this source has made improvements to the design that make the current Radio Snack specs obsolete. It is quite possible that the meters are much better than their specs suggest. BTW, one of you brought up a good point in discussinig +-level vs. +-response. Keep in mind that when you say somethig is +-3dB over a frequency range, it's response can be ANYTHING within a 6dB window over that range. For example let say the spec is +-3dB 50Hz to 5kHz. A response that is flat +3dB form 50Hz to 500Hz, and then falls to a flat -3dB from 600Hz to 5Khz actually falls withing the +-3dB spec. As another example, a flat response all the way from 50Hz to 5Khz with a + OR - 6dB peak somewhere also fits the +-3dB spec.

You guys are correct. I am spoiled. My own mic is a laboratory standard from Denmark, +0.5B, -0dB from 5Hz to 20khz. My work demands high accuracy. Also, this mic is nice to use as a calibration mic. Very often I need to do a plane wave tube measurment, or horn throat measurement or an in cabinet measurement, and I don't want to risk destroying my $2,000.00 Bruel and Kjaer Lab mic. I can do a really nice calibration with a low cost condensor mic and put the lower cost mic in "harms way".

BTW, most of the low cost sofware packages out there DO allow you to use your sound card and low cost mic as and SPL meter. AND a FFT analyzer, AND an impusle measurement tool, etc., etc., etc.. You can also use this set up without a mic and measure all the important parameters of any electronic equipment you have.

Carlos

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post #98 of 212 Old 05-31-2006, 05:37 AM
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Quote:


I thought the measurments posted by Bruce were using individual calibration files. I am a bit confused still, but after re-reading, it appears he used some "standard" calibration files.

The standard we used to create the three new calibration files for the three types of RS meters was a professionally calibrated ECM8000.

To verify and test the two latest calibaration files (namely the new analog and the new digital), we took a response measurement of the ECM8000 using its calibration file, then we took a response measurement of two new analog meters using the single new analog calibration file and we also took a response measurement with two new digital meters using the single new digital calibration file.

As much care was taken as possible to remove as many variables and the 5 sweep are shown on the graph in my previous post. This was a test to see if we did a passable job and also to show how much meters of the same kind can vary. We decided our cheap and dirty calibration files were good enough to use and also for anyone else who cared to use them.

Quote:


BTW, most of the low cost sofware packages out there DO allow you to use your sound card and low cost mic as and SPL meter. AND a FFT analyzer, AND an impusle measurement tool, etc., etc., etc.. You can also use this set up without a mic and measure all the important parameters of any electronic equipment you have.

REW software allows you to do all this and much more.... and it's free

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post #99 of 212 Old 06-01-2006, 05:28 PM
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thought i'd add some more data to this thread....Ed Mullen and I compared my RatShack Analog meter to his M30BX back in March. here is the data we too 15-90Hz...

http://www.cyberfrogs.net/files/M30B...S%20Analog.txt

I've also got a bunch of truerta files with pink noise and quick sweeps of each meter id anyone is interested....just PM me.
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post #100 of 212 Old 06-01-2006, 05:49 PM
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i should note, that the measurements were taken from the needle not the line-out on the meter. The numbers look pretty nuch in line with the RSAnalogueSPL.txt that was posted in another thread.
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post #101 of 212 Old 06-01-2006, 06:06 PM
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here is the truerta shot of the M30BX (green) vs the RatShack (purple) using pink noise:

http://www.cyberfrogs.net/files/M30BX%20vs%20RS.PNG
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post #102 of 212 Old 06-01-2006, 06:19 PM
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Which model analog meter was used?

Of course taking the measurements from the needle would mean the measurement is C-weighted. Not sure if Truerta compensates or not since I'm not familiar with the program.

Interesting though.

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post #103 of 212 Old 06-01-2006, 07:11 PM
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Quote:
Originally Posted by Sonnie Parker View Post

Which model analog meter was used?

Of course taking the measurements from the needle would mean the measurement is C-weighted. Not sure if Truerta compensates or not since I'm not familiar with the program.

Interesting though.

the old analog meter was used. i dont believe truerta applys c-weighting.
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post #104 of 212 Old 06-01-2006, 07:27 PM
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Quote:
Originally Posted by Sonnie Parker View Post

Which model analog meter was used?

Of course taking the measurements from the needle would mean the measurement is C-weighted. Not sure if Truerta compensates or not since I'm not familiar with the program.

Interesting though.

if i use your values and REW for the old analog meter, should i tell REW that c-weighting was applied or not applied?
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post #105 of 212 Old 06-01-2006, 08:01 PM
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Sonnie,

I've removed the C-weighting from the needle values that I showed in the linked txt file. Here are the results, both of our results are within a couple dB:

Hz Correction

15 -16.34361941
16 -15.22756225
17 -13.68583066
18 -12.40894914
19 -11.1888943
20 -10.21882506
21 -9.492874248
22 -9.00598465
23 -8.353778216
24 -7.832450254
25 -7.338682945
26 -7.069573988
27 -6.422577243
28 -5.895453034
29 -5.586226304
30 -5.093151186
31 -5.014680894
32 -4.649442029
33 -4.59621258
34 -4.453903023
35 -4.121540044
36 -3.998252482
37 -3.783259158
38 -3.575858312
39 -3.675418416
40 -3.481370171
41 -3.39319951
42 -3.110441486
43 -3.232674904
44 -3.159517608
45 -2.990622339
46 -2.92567308
47 -2.664381826
48 -2.606485729
49 -2.251744577
50 -2.099938539
51 -2.150866179
52 -2.004342674
53 -2.160198236
54 -2.018276696
55 -1.878434238
56 -1.940538272
57 -1.904466415
58 -1.97010558
59 -2.237351156
60 -1.906106274
61 -1.876281135
62 -2.147792413
63 -2.320562714
64 -1.894520079
65 -1.869597544
66 -1.645732732
67 -1.72286749
68 -1.800947551
69 -1.679922234
70 -1.259744167
71 -1.140369031
72 -1.421755334
73 -1.103864198
74 -1.386659165
75 -1.570106024
76 -1.454172644
77 -1.33882883
78 -1.024046185
79 -1.109797983
80 -1.096059054
81 -0.782805679
82 -0.870015492
83 -0.757667385
84 -0.74574143
85 -0.934218801
86 -1.023081698
87 -0.712313285
88 -0.901897628
89 -0.691819638
90 -0.882065017
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post #106 of 212 Old 06-01-2006, 09:07 PM
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You can have REW compensate for C-weighting and C-weighting will be applied to frenquencies where there are no correction values, but from 100-200hz there's not enough adjustment from C-weighting to matter... less than 1db. So... ultimately it doesn't matter if you compensate or not for the sub measurements.

This is really good that you have posted this. It proves yet again that the old long time used RS correction values that were floating around the net for years and years are just not accurate. Like you say... just glancing through a few of the numbers, we are within a couple db of each other. I don't know for sure without inputting both into a spreadsheet, but I suspect if we made a 1db across the board adjustment to either set of values (to account for the level variation)... we would then be within 1db of each other. Either way... what we see is perfectly acceptable from meter to meter and either set of values would get us really close. If you smoothed your response we'd probably be again closer. There are several variables that could cause our minor differences, but we've all done well to provide others with better and more reasonable values.

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post #107 of 212 Old 06-02-2006, 01:17 PM
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Of course, it's possible that RS made some changes to the innards of the "old" meter somewhere in its past, so that the correction values were once valid.

No matter where you go. ... There you are.
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post #108 of 212 Old 06-02-2006, 01:38 PM
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I'm thinkin' that is what happened because I remember back in 2001 a fella right here on AVS tested those older correction values to be correct at that time. Somewhere along the line I can't help but to believe RS upgraded the units to be a little better.

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post #109 of 212 Old 06-02-2006, 01:47 PM
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Quote:


but I suspect if we made a 1db across the board adjustment to either set of values (to account for the level variation)... we would then be within 1db of each other. Either way... what we see is perfectly acceptable from meter to meter and either set of values would get us really close. If you smoothed your response we'd probably be again closer.

I imported PLincolns calibration file into REW as if it were a frequency response text file and then did the same for the HomeTheaterShack old analog meter calibration file to see how they compared. You can see for yourself from the attached graph that they are very close - (note the Plincoln file is only from 15Hz to 90Hz). I only needed to do a small wholesale gain adjustment on one file as sonnie suggested to match measurement level variation.

I think we can presume that the new calibration files at sonnies site on the downloads page are fairly accurate.




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post #110 of 212 Old 06-02-2006, 01:50 PM
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bruce,

thanks for taking care of that....i was planning on doing the same thing today, but I can't seem to pull myself away from listening to the ascends that arrived today.

it is certainly a good comparison to have...two different calibrated mics and two different people running the same experiment....and then have similiar results. I guess I should have posted this information earlier...
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post #111 of 212 Old 06-02-2006, 02:32 PM
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Yeah... excellent graph comparison. Thanks brucek!

This is again so very good... as you say PLincoln... two different people, two different calibrated mics, and also two different RS meters that were more than likely manufactured at different times.

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post #112 of 212 Old 06-03-2006, 07:27 AM
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Guys,

Some "Ray" guy published a MASSIVE list of great links in another thread. Many to useful gear and software. There is also a bit of discussion there that has crossed paths with this thread. The thread is here.

ALSO, I am into R/C airplanes, and this upcomming Wednessday I am calibrating the 3-4 club SPL meters (R/S for the most part) at the club meeting. I may take the time and do some more fooling around while I have 3-4 of them on hand at the same time. I will let you know what I discover.


Carlos

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post #113 of 212 Old 06-03-2006, 02:55 PM
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That would probably be very helpful if you could compare those Carlos... thanks!

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post #114 of 212 Old 06-07-2006, 10:21 PM
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Tonight was our Monthly club meeting and I had a chance to look at four R/S SPL meters. We also saw some awesome videos of R/C plane crashes (mostly of the turbine variety). My god some of those planes were totally destroyed. ANYHOW, moving on.....

Three of the four meters were analog, and one was the newer digital one. The analogs seemed to vary in both age and abuse by a good margin.

Calibration for level: The digital meter was within 0.5dB of my Lab Mic, two of the analogs were low by 1 dB and one of them was high by 1 dB. Not bad at all, especially considering the brutal conditions these mics are always used in (around loud, high crest factor airplanes spewing spent fuel all over the place).

Comparing the response to the B&K lab mic: Unfortunately, two guys had to leave the meeting early, so I only looked at the digital and one of the three Analog SPL meters for response. The results were impressive, and interesting. First of all, the response differences between them was very small (I was only looking at 1Khz and lower). More importantly, if you applied an inverse C weighting curve, both of the responses would be close enough to flat for most DIY purposes. I was truly impressed. These meters are much better than when I last looked at them (many years ago).

Thread Summary: (If I may be so bold....after all, I did take the time to re-read most of the posts on this thread )
1) Standard weighting curves for these meters HELP
2) The response below about 40Hz CAN vary from meter to meter, and sometimes it CAN be very close. Lots of good data on this thread seems to suggest that there is certainly a response GOAL for these meters that is USUALLY held to, but sometimes this goal is simply not realized in the lowest octave.
3) There is some data that shows that the digital meter output is C-Weighted, and some data that shows it is not. The reasons for this are not known at this time. The low end may simply vary that much, or there may have been a design change at some time, or it could be a result of a manufacturing "glitch" of some kind.
4) The meters are substantially more accurate when used for what they were intended for than their specs suggest (looking at basic C Weighted and A Weighted SPL), and the response for much of the room dominated response range (300 Hz and below) is pretty accurate and smooth.
5) The meters are not conistant ENOUGH to be considered accurate in the last octave (below 40Hz) without INDIVIDUAL calibration OR AT LEAST COMPARISON to a reference of some kind.


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post #115 of 212 Old 06-07-2006, 10:42 PM
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Good info Carlos... thanks for taking the time to check those out.

Btw... I haven't forgot about you on the call. It's been unreal, as you can imagine.

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post #116 of 212 Old 06-11-2006, 04:08 PM
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well i had a chance to play around with my new calibration files (that removed the adjusting for the c-weighting) today...I still have to decide how I feel about the new curve. I spent a couple hours with REQ and TrueRTA to get as flat as a response as I could with my rane pe-17

with the new calibration file (sonnie's or mine) there is a huge amount of room gain evident from 22hz down that was masked when using the old cal files. after pushing those peeks down nearly 10-12db, the new flat curve is taking some time to get used to. clearly some of the boomy-ness is gone, but as one would expect, the impact down low of the IB is now "less".

Since I "thought" my setup was flat prior to this new adjustment, I always thought flat sounded real good....when in reality i was listening to c-weighted flat which included the lift at the lower end....I will watch a few movies this way to see if I can adjust to the true flat sound.

I may borrow my friends mic and preamp so i can once an for all eliminate the ratshack meter as part of the problem.
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post #117 of 212 Old 06-11-2006, 06:40 PM
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well I'm just thru the first disc of Pearl Harbor (great flic, btw) using the flat curve, and all appears to be well. I think my concerns will be diminish after viewing a few more flix. There is plenty of low end even with the flat curve, without being bloated or over powering. I doubt I will remove any of the low end cut that I applied.

I will post back after a couple more movies and some more tunes.
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post #118 of 212 Old 06-11-2006, 07:06 PM
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Flat usually will sound flat... this is why many will choose to optimize to a house curve for movies and flat for music. The house curve will get that low end back for you without the boominess... where you can really appreciate your IB's and what they can do.

Wayne P. does a nice job of explaining the house curve in this sticky thread .

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post #119 of 212 Old 06-16-2006, 07:58 PM
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I have just used the new correction tables and my RS (old) analog SPL meter to equalize my subwoofer. I found the new correction table to be far more accurate than the older readings, sub and system have never sounded this good.

Thanks to all who contributed to figuring these out, I knew there was a reason I regularly cheched these forums :-)
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post #120 of 212 Old 08-19-2006, 05:06 PM
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A little new in the audio area so please bare with me.

Since I was interested in calibrating my TV and figured I'd do the HT audio calibrated as well. I got my hands on an old RS SPL meter and have been searching for the right correction tables to use.

Way ealier in this thread post #10 there are some tables that I figure I add the second column to the reading at a given frequency,but after 160hz there are 3 columns:

http://www.avsforum.com/avs-vb/showt...&&#post5272422


Since thera are tables floating on the web that are different, are these the right tables for my old analog meter? What is the third column for?

Thanks!
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