A friend of mine wanted to have his newer type analog Radio Shack SPL meter calibrated, so he sent it to me. I noticed some strange behaviour while calibrating it against to my professionally calibrated microphone. The amount of correction needed wasn't anywhere near to what Sonnie's correction file suggest for this type of meter. I believe a few graphs explain it better. All the measurements were done with the REW (4.00), I merely used the TrueRTA to show them.
The first graph shows the difference between the correction files for my (i.e. my friend's) new analog meter and Sonnie's new analog meter. Quite a difference!
The second graph shows the difference between the correction files for my new analog meter, my old analog meter, and Sonnie's old analog meter. As you can see, they all match reasonably well (within ~3 dB). My new analog meter seems to be only a little bit better than the old ones.
So what does this all mean? Assuming both Sonnie and I took accurate measurements, some of the new analog meters are better then the others. The worse ones aren't much better than the old analog ones. This will definitely cause some strange measurement results when all the people having the new analog meter are using the same correction file. Their frequency response can look like having much more low frequency roll-off than it in reality has.
So it looks like some of the new analog meters are still having the insides of the old analog meter. How do we separate them? I took a picture of the QC stamp, which reads "10A05".
Could people post their QC codes for all the RS meters they have?
Here's the list:
New analog (soft-look)
04A06 (tatkinson)
12A05 (Chrisbee, toecheese)
10A05 (Ilkka's friend)
06A05 (WillyD, Average Joe)
4A05 (norpus)
02A04 (JRace)
Old analog (boxy)
07A06 (Jeffeory)
11A05 (daxie)
12A03 (Ilkka)
10A02 (Peter De Smidt)
09A01 (snatcher)
9A4 (Chrisbee)
