2way speakers

B&W crossover a 6 inch woofer at 4 KHz (big mid range hole) and tend to boost their bass response too

B&w are using true phase cohesive first order filters so the discontinuity in off axis response is not as sharp as you think it is.

Anyway nobody should be listening in an untreated room so the importance of off axis response depends on your room acoustics.

If you move up to 3way in an attempt to even the polar response you now have further problems with trying to merge three drivers to make them sound coherent. You will need a bigger cabinet too.

As for boosting the bass, that's dependent on room and positioning too. There is no correct answer to how much boost there should be. You don't want the speaker to sound too thin or too warm or bassy. The response shown on the graph depends on how the measurement was taken

@kenjit

You are assuming that I stated that even frequency response and even dispersion is the only criteria for evaluating speakers. It isn’t. Dr Floyd Toole research conclusively demonstrated that these two factors are however extremely important.

To name just a few other important factors that a good speaker design must consider:-

Waterfall plot. Power compression. Crossover design & quality. Q of the bass response. Dynamic range. Intrinsic driver damping. Driver break up. Short coil in large magnetic gap (for linear response). Low hysteresis. Good driver alignment (no rocking motion). Good voice coil cooling from extremely tight tolerances to reduce thermal compression. Baffle design. Port design. Impedance and amplifier load. Driver sensitivity matching. Phase alignment of drivers.

But you didn't mention any of those before. You simply chose to focus on the response. 

@kenjit

My apologies. Let me know what else you want to discuss in more detail. I am sure the experienced folks at Audiogon can help. There are extremely few speaker designs that don’t have any weaknesses at all but ATC and Harbeth are up there among the better designs that have withstood the test of time.

Fitz and Monitor Audio.