Originally Posted by
RMC
In his Loudspeaker Handbook 2nd ed, Eargle explains these, as well as a method using ground plane measurements to approximate anechoic measurements usually done in full space, including a response graph showing Ground plane, anechoic and half-space (P. 340-1). There's also the open field environment mentioned which is similar to ground plane. "It is often built on a roof top, where there are few space limitations." (...) "The open field is often referred to as a 2Pi, or half-space, measuring environment." (p. 335-6) I can't reproduce the interesting typical curves shown for the three. However, curve shape is the same for anechoic and ground plane, though there's a level difference between these two, which looks like 6 db or so. As for the ground plane vs half-space curves, from 100 hz going down, they're identical. Hopefully the above will help you. Richard