>>Anechoic...is theoretically "non-echo" in an open environment...like outdoors on a pole, as you mentioned. So rolloff due to chamber size makes no sense for anechoic measurements.
Ahh, but that's the whole point. The low frequency cutoff is where the anechoic chamber stops being anechoic. This was the first link I found that talks about it in more detail :
"An anechoic wedge is designed to provide a normal-incidence sound absorption coefficient greater than 0.99 for all frequencies down to its design cutoff frequency. Reflected sound from such a wedge is attenuated 20 dB or more. An anechoic wedge is typically one-quarter wavelength long at its cutoff frequency. For example, a 100 Hz cutoff wedge is usually approximately 36 inches long."
http://zone.ni.com/devzone/nidzgloss.nsf/webmain/62E64F4028A2D77C862568C6005E4B84?OpenDocument 
