Is it really a good idea to use the natural on-axis response of the loudspeaker as a sort of de facto room-response equalizer? Such an approach seems to be both counterproductive and counterintuitive.
Bashers? Now that sounds a bit harsh.
The issue presented by the non-flat measured response of the B&W 801 D4 is indeed addressed by Toole's research:
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What has been found over several decades of conscientious investigation and publication is [that]...in double blind tests in normally reflective rooms (different ones over the years) listeners give the highest ratings to loudspeakers that measure essentially flat and smooth on axis, and at least smooth off axis in an anechoic chamber or functional equivalent. What they are recognizing and responding favorably to is the absence of resonances - i.e. neutrality."
It would seem that, by definition, the measured response of the B&W 801 D4 is not neutral (i.e., it is colored).
Even as far back as 1975, the B&W DM6 had a relatively flat on-axis frequency response (see below).
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Then, as tested by Audio (November 1990), the B&W 801 also had a relatively flat on-axis response (see below).
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Both the B&W DM6 and the B&W 801 avoided having a boosted on-axis high-frequency response.