Outta space in the legend:
The Smaller Advent #853 +2.5 dB from KLH-6 = Red, and AR3a #368 +2.75 dB = Blue:
Discussion:
Nearfield measurements reflect 2-Pi performance, i.e., with one boundary of bass reinforcement, which is typical of how vintage East Coast speakers were intended to be used.
Published frequency response curves are often anechoic, i.e., 4-Pi freespace, no boundaries. To the best of my knowledge, however, there are and never have been any anechoic chambers large enough to measure accurately down to, say, 20 Hz. Thus, the published results may be "corrected" via calculation as required for publication. A speaker buried in the ground as practiced by AR is 2-Pi.
I am measuring at the grille, not the woofer dome, the reason being that the particular pair of KLH-6 which launched this compariion are the sealed version, with the grilles not removable. The several that I did check both ways did not vary significantly, though a valid argument may be made that, as consequence, these measurements are progressively less and less accurate above 200 Hz.
Another issue is how to normalize the measurements. You can see that I have tried to make them all equal in the 300 - 500 Hz range, and noted the SPL level adjustment for each relative to the subject KLH-6s, and these are reasonable given the known sensitivities of the various models.
Still, I believe there are valid conclusions to be drawn here, which, for now, I leave to readers and students of "classic" loudspeaker design....
