The need for annual calibration has been mentioned by others, but it's also exaggerated, imo. I agree with you. It still happens to be the standard practise due to historical reasons. Meters and calibrators didn't use to be before as stabile as they are nowadays. And of course calibration labs need...

The ND9 was within 0.1 dB of all the others. Do you know how the mic capsule volume, atmospheric pressure, temperature and relative humidity affect the calibrator’s frequency and sound pressure? Your sample of the ND9 can be good in one test now, but only a long term multiple units testing with d...

Congratulations for your new setup. It is really impressive. It was also nice you shared this building project with us. I've also done some amateur work in this field. It is easy to agree with the decisions you have done. Only the sound calibrator left me wonder if it is up to the quality of other e...