I came across the following post regarding some background on why band limited (500 Hz to 2 kHz) pink noise is the preferred source to set acoustic levels. This is in reference to page 46 of the guide, when one is carrying out the mic calibration.
"With low-frequency components present, there’s lots of level bouncing around, and when played back in a room, the effects of standing waves are to add a frequency-by-frequency ±15 dB variation to the level typically. One way to solve this problem is to band limit the noise to above the Schroeder frequency; that room-volume dependent frequency where not much else above it in the soundfield can be called diffuse. For small rooms, 500 Hz will do.
At the high-frequency end of the range, there’s lots of trouble, too. Half-inch measurement microphones exhibit an 8 dB difference between direct sound and diffuse field sound at 20 kHz, and 6 dB at 10 kHz. These are big differences that will show up in an overall measurement, depending on whether you are direct- or diffuse-field dominated, and which way you aim the mic. Also, for interchangeability with the largest range of differing systems where “house curves” or the X curve of motion picture sound is in effect starting their rolloff at 2 kHz, rejecting frequencies above 2 kHz leads to maximum utility.
So pink noise, band limited to 500 Hz to 2 kHz is the preferred source to set acoustic levels.
It is broad enough so that single-frequency standing waves don’t make the measurement inaccurate,
and narrow enough that low- and high-frequency acoustical and sound system effects are minimized.
Using this two-octave band noise also solves another problem. The standard of the motion-picture industry for level setting is the ubiquitous Radio Shack sound level meter. Everybody should have one.
Get the cheaper analog meter that has better resolution than the more expensive digital one. I have calibrated more than 100 of these meters over a period of years, and find them out of the factory to mostly be within 1 dB, pretty good for such a cheap device. However, they do vary one to the next in their C weighting filter, so that broadband noise may show a different level meter-to-meter when they are calibrated on a mid-range tone (or noise)."
I believe the above is written by Tomlinson Holman, co-founder and Chief Scientist of Audyssey and the TH in THX. Is it worthwhile to consider this?
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Last edited by steveting99; 06-23-2014 at 09:21 PM.
Reason: correcting typos