I have watched today with interest, and sometimes amusement, as various thread participants expressed their views on the burning issue of whether the REW microphone needs to be calibrated or not. I feel compelled to add my comments.
Issue 1: Can REW capture meaningful measurements upon which we would base decisions regarding listening room improvements without calibrating the microphone?
My opinion: Yes. The only variable affected by microphone calibration is the vertical location of the measurement line in the graph. Within the same REW session, different measurements can be taken and compared, and the positioning on the vertical axis of the measurement lines has no bearing on being able to make valid comparisons. Having said that, without calibration the measurements could have vertical axis differences across different REW measuring sessions, and could make interpreting the graphs somewhat more difficult for the average user. Bottom line: calibrating the microphone adds a level of consistency and repeatability to REW measurement that some may find appealing. Recommendation: calibrate, or don’t calibrate, depending on your personal preferences, and as long as you know the impact of not calibrating.
Issue 2: Is a SPL meter absolutely required to make a meaningful calibration?
My opinion: No. While a SPL meter is a more accepted method of calibrating to a known external sound level, there could be other equally acceptable methods. Take, for example, the AVR speaker test tones. When the test tones are invoked, a properly-calibrated system will produce a sound level of 75dB, when measured with a SPL meter at the MLP. At least one of you claims that the test tones are at 75dB only if Audyssey is turned off. This is not an issue—simply turn Audyssey off, calibrate the mic, and the mic stays calibrated for any subsequent measurements, whether Audyssey is off or on, DEQ is off or on, etc. In summary, an alternative method of calibrating the microphone is to output the speaker test tones, open the REW SPL, click Calibrate, and enter 75dB for the sound level. I tested this today, and it works just fine. So, for those who don’t have a SPL meter, and don’t want to purchase one, this is an acceptable alternate calibration process.
So, who was right, and who was wrong? It doesn’t matter. We need to move on to more meaningful dialog around actual measurement and analysis, now that the microphones are arriving. If anyone’s feelings have been hurt, we all need to apologize to one another and keep our thread focused and on topic.
Edited by AustinJerry - 2/4/13 at 5:12pm