jdm56 Posted April 3, 2006 Share Posted April 3, 2006 I've had an analog RadioShack spl meter for quite a few years, and like most, it's been dropped a time or two, sat on, kicked and had it's needle pegged about a jillion times...so I'm wondering about that little calibration thingy. How does one get one of these gizmos calibrated? Wouldn't it be better to just buy a new one at this point? And a related question --which I think I have seen here before, so I will do a search-- z'inybody got a list of corrections for the meter's known deviations from accuracy? ------------------------------------------------------------------------------------------------------------------------ Ah! here we go... At 10Hz add 20dBs to the meter's readings and at ...12Hz add 16.5dB16Hz add 11.5dB20Hz add 7.5dB25Hz add 5dB31.5Hz add 3dB40Hz add 2.5dB50Hz add 1.5dB63Hz add 1.5dB80Hz add 1.5dB100Hz add 2dB125Hz add .5dB thanks to Michael Hurd and his post from February '05 for the above correction info. Quote Link to comment Share on other sites More sharing options...
Schurkey Posted April 4, 2006 Share Posted April 4, 2006 A much more comprehensive set of corrections is available at: http://www.hometheaterhifi.com/utilities-download-page.html Do keep in mind that Radio Shaft has "upgraded" the analog meter, and added a digital meter, and, by now, probably discontinued both again. [edit: The digital 33-2055 is still current. My analog 33-2050 is not listed on the RS web site.] Somewhere, I remember seeing a solder project where you go in and actually CORRECT the defect [edit: in the analog 33-2050] by adding resistors, capacitors, etc, rather than looking at a cheat-sheet all the time. When (if) I find it, I will post an update. Quote Link to comment Share on other sites More sharing options...
Schurkey Posted April 4, 2006 Share Posted April 4, 2006 The solder project WAS hosted at: http://www.gti.net/wallin/audio/rsmeter/33-2050/33-2050.html This link is no longer active--at least when I tried it just now. It was for RS # 33-2050 meter. Perhaps it is being hosted somewhere else, and I just don't know about it. Quote Link to comment Share on other sites More sharing options...
Schurkey Posted April 4, 2006 Share Posted April 4, 2006 DELETED Quote Link to comment Share on other sites More sharing options...
Schurkey Posted April 4, 2006 Share Posted April 4, 2006 FOUND! CALIBRATION INSTRUCTIONS FOR THREE MODELS OF RADIO SHAFT SPL METERS: 33-2050, 33-2055, 42-3019 See the links at Eric Wallin's "new" page http://home1.gte.net/tammie_eric/audio/audio.html And a review of the modified meter: http://www.stereotimes.com/acc032902.shtm Quote Link to comment Share on other sites More sharing options...
DrWho Posted April 4, 2006 Share Posted April 4, 2006 Oh wow, I've been looking for that website for a while now...there were a few people asking me about upgrading their rat shack meters - now I gotta go figure out who they are [] As far as calibrating your meter...you will need to go find someone with a calibrated meter to go compare against. The one I have seems to be calibrated pretty well...my acoustics teacher brings in a fancy $2k calibrated meter every day. One of these days I should bring mine in and do some comparisons. Quote Link to comment Share on other sites More sharing options...
Kriton Posted April 4, 2006 Share Posted April 4, 2006 OK, wait - does the digital meter not have these problems? Second, assuming I don't know what your are talking about, what do we do with the above calibration adjustments? I am thinking you place the test tones at those hz levels, and it you are getting say an 65db reading, you add the adjusted numbers above to get a true level? Please explain how the adjustments work, and under what circumstances. If you have any further links to using the meter beyond just individual speaker level adjustment, please post (the user manuls are pretty useless, you would have to agree). Thanks! K Quote Link to comment Share on other sites More sharing options...
DrWho Posted April 4, 2006 Share Posted April 4, 2006 The digital meters have the same problems...they post frequency response plots in the manual that comes with the meter. To calibrate the ratshack meter, put on some broad band pink noise and then measure with a calibrated meter. Bring your ratshack meter up next to the other meter and turn the calibration knob until it reads the same level. As far as uses for the meter...it is best used for individual speaker level adjustment and then can also be used to give you an idea of how loud you're listening. The microphones in these units do not have a flat enough response to be used for any form of RTA or ETF application. For $100 you can get yourself a calibrated mic ($50 from behringer) and then you'll need a mixer of some sort with phantom power ($50 2 channel behringer mixer). Then all you need is a computer and there is plenty of free software to make you go crazy. This would be a very good measuring system and it doesn't break the bank either. And for an additional $200 or so you can get some very powerful ETF software too... Quote Link to comment Share on other sites More sharing options...
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