Shady... I see you like to use a parking lot, IIRC... Ricci goes into a field...
Is there a right or wrong way to do ground plane measurements in terms of Surface? Flatness? what would be the minimum Open Area advised for accurate GP Measurements?
Many thanks!!!
All you need to do is eliminate the acoustic reflections, and both a parking lot or field can do that. I have tested in both conditions. You just need to place the mic on the ground so that no reflections can bounce back up into the mic. With the mic tip on the surface, everything it gets is a direct sound and not a reflection. The nature of the surface doesn't matter that much (at least for low frequencies).
The minimum openness of the area depends on the lowest frequency of interest since we need at least one wavelength from any reflective structure. A reflective structure is pretty much any large building or large solid surface. So let's say you wanted to test 10Hz, well, the wavelength of 10Hz is 113 feet, so you can't have anything large closer than 113 feet from either the mic or the sub.
One of the biggest problems in sub testing is simply finding an area where it can be done. So you need a wide open area, but one that also has access to an AC output, and also has a low noise floor, so it can't be done near a major roadway or loud industrial area. That is a tall order, especially when you live in an urban or suburban area. What can also complicate things is that these test tones are usually louder than noise ordinance will allow, so that means it can be tough to do in a field in a residential area like a soccer field or baseball field. I have a good testing site at the moment, but I have to drive 2 hours just to reach it since I live in a Chicago suburb (I hope you ingrates appreciate those subwoofer measurements because that commute is murder!)