Posted January 10 2002 - 08:53 AM
There are several schools of thought on this issue. The two that strike me as the most logical are:
Method 1 -- Point meter straight up. The logic here is that your ears are more in line with the surrounds, and hence seem louder. Therefore, holding the meter straight up puts its mic more in line with the surrounds, reducing the bias to the surrounds and giving you a more balanced soundfield. The problem with this method is that the Radio Shack SPL meter, despite its claim of being non-directional, DOES exhibit some reading differences (up to 2dB) when severely off-axis... hence METHOD 2.
Method 2 -- Angle meter forward. The 45 degree rule is a good rule of thumb, but there's more to it than that. Logic tells us that the further away from being on-axis, the more variation we will have with the SPL meter. Therefore, the only way to get a true unbiased reading from all speakers is to angle the meter so that all speakers are at roughly the same off-axis angle. In other words, point your meter at a point on the ceiling and look at the angle between the microphone's axis and the front speakers... then compare this to the angle between the microphone's axis and the surrounds. Angle the meter so that these two angles are as close as possible to being the same. Then, with the meter in this angled position, perform the calibration. In my room, this puts my SPL meter about 30-35 degrees from vertical.
Your mileage may vary, but method 2 gives me the best results and sounds well balanced.