Originally Posted by LTD02
everytime that i go back to his site, his measurements change, i can't keep up.
look what he has now: http://www.gedlee.com/summa_.htm
i suppose this one wasn't generating as many sales as it was questions.http://www.avsforum.com/avs-vb/showt...7#post17831507
with the first line being on axis and then each additional one being 7.5 degrees, the -6db point appears to be around 45 degrees at about 1khz. (purple line) it is always possible that i read this plot wrong.
Yes, but notice in the individual polars that the SPL is "normalized." That's standard practice in conventional polar plots for determining the effective beamwidth. The off-axis may be down in SPL overall, but so long as the curve itself stays within the -6 dB limit, it qualifies.
His "new" directivity presentation is deceptive in several ways -- the designs are EQ'd for flattest performance at his intended design axis, somewhere in the range of -20°, where he has "set" the white-line cursor, generating the flatish FR across the top graph. To compensate for the fact that the overall SPL is down from true axial, the color scale is offset for this "normalization," and the response anomalies there obscured; the white cursor does not pass through them.
In the exhibit shown, "0" occurs at something more like -3 dB, whereas, in his recommended extreme toe-in deployment, it's "true" zero, including those anomalies, that is illuminating the opposite wall and generating the first contralateral reflection. He might legitimately argue that since the delay is long, this is not affecting imaging, but not so effectively, tonality or timbre.
Notwithstanding these qualifications, however, the black contour line represents -6 dB for Summa, and you can see that the beamwidth varies between 70° at ~1.5 kHz and ~85° at 7.5 kHz. Nowhere within the bandwidth of interest is it 90° "nominal."
Last time I looked, Summa as shown in his directivity paper more accurately illustrates the actual behavior of the product. There's nothing dishonest here; he's merely illustrating the performance in its best light, consistent with how he has designed it and recommends that it be used. There IS a bit of sleight of hand involved in the presentation, though, obscured by a gratuitous "No other manufacturer would DARE show their data in this level of detail" smoke screen....