PSB Synchrony One

Response curve is an average of five measurements:
on-axis, 15 degrees left and right off-axis,15 degrees up and down off-axis

0 / 15 / 30 degree off-axis responses

THD+N @ 90dB (50Hz - 10kHz)

With regard to objective evaluations, PSB Synchrony One is one of the best measured audiophile loudspeakers. I love their nearly-constant direcitivy, truly full range response with great linearity, Needless to say, their price of $4500/pr is extremely competitive comparing with other competitors in the same league (look at the price tags for Wilson Audio Sasha W/P or Revel Ultima Salon 2).

Source: http://www.soundstagenetwork.com/measurements/speakers/psb_synchrony_one/

Bowers and Wilkins (B&W) 800 Diamond

Free-field response (Semi-anechoic)

Acoustic Contribution

Horizontal Directivity

Vertical Directivity

This set of measurements doesn't look bad. But small linear distortion in midrange is appeared. Directivity pattern is not very generous for the price range.

Source: http://www.stereophile.com/content/bampw-800-diamond-loudspeaker-measurements

Bowers and Wilkins (B&W) 802 Diamond

Free field response of 802 Diamond (Purple trace)

On-axis response is clearly less linear than previous B&W models. Some argue that new midrange units of Kevlar cone might result in such linear distortions.

Source: http://www.hometheater.com/content/bampw-802-diamond-speaker-system-ht-labs-measures

Martin Logan Vista

Lots of dips and peaks are shown in measurements of electrostatic loudspeakers. And it is not quite sure whether such tricky patterns imply acoustic inferiority, although one of recent studies conducted by Olive show listeners may prefer flat-responding typical loudspeakers to Martin Logan's ESL.

Source: http://www.homecinema-fr.com/forum/materiel-haute-fidelite/jeu-des-4-enceintes-inconnues-t29979561-15.html

Infinity Prelude P-FR

These loudspeakers have not only very good characteristics - flat on-axis response (as well as listening window average) and gently upward DI - but also very deep bass extension. Truly full-range.

Source: http://www.homecinema-fr.com/forum/materiel-haute-fidelite/jeu-des-4-enceintes-inconnues-t29979561-15.html

Altec A7-500 Loudspeaker system

Found the frequency response (guessing it's an on-axis free field response) and and vertical directivity sonogram. Looks very nice. Especially so considering their ages!

Source: http://www.seeko.co.kr/zboard4/zboard.php?id=forum_etc2_1&no=28238