Audioengine 2 (A2)

Fig.5 Audioengine2, anechoic response on tweeter axis at 50", averaged across 30° horizontal window and corrected for microphone response, with the nearfield responses of the port (red) and woofer (blue) plotted below 700 and 300Hz, respectively, and the complex sum of the nearfield responses plotted below 300Hz (black).

Fig.6 Audioengine2, lateral response family at 50", normalized to response on tweeter axis, from back to front: differences in response 90–5° off axis, reference response, differences in response 5–90° off axis.

These loudspeakers are very cute, but have well balanced response and relatively deep bass extension considering its driver unit size. But be careful that such bass extension is due to strong electronic amplification (see below).

Fig.2 Audioengine2, built-in amplifier frequency response at 1V into 8 ohms, measured at right-channel speaker output jacks (2dB/vertical div.)

Source: http://www.stereophile.com/content/audioengine-2-powered-loudspeaker-measurements

Creative GigaWorks T20

If one is looking for very budget-wise (<$100) but do not want to lose acoustic quality too much, Creative GigaWorks T20 is something he/she must consider. Their vertically-angled design is also highly useful when they are placed on the desk without any external stands.

Source: http://www.ixbt.com/multimedia/creative-gigaworks-t20.shtml

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/

Revel Ultima Salon 2

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

On-axis, 15/30/45/60/75 degrees off-axis responses

Total Harmonic Distortion

If objective measurement can account for most of audiophile-level listening pleasure, Ultima Salon 2 is clearly a perfect loudspeakers for home hifi: wide frequency range, flat free-field response, good directivity pattern, and very low distortion over entire frequency range.

Source: http://www.soundstagenetwork.com/measurements/speakers/revel_ultima_salon2/

Yamaha NS-1000

Measurements should be interpreted very carefully because it's not a free-field response but a in-room response, although the room where NS-1000 was measured behaves very well.

You can also find an alternative crossover design that is claimed to do better than the original one of NS-1000 in terms of harshness in mid/treble.

Source: http://www.troelsgravesen.dk/Yamaha-NS1000.htm

Yamaha NS-10M

FIGURE 18.22 Two small 7- to 8-in. two-way loudspeakers with similar directivity indexes, each one optimized to a different target. (a) The Yamaha NS-10M was designed to have constant sound power. (b) The JBL 4301 was designed to have constant on-axis frequency response.

FIGURE 18.23 (a) and (b) show that the Yamaha NS-10M performance drifted from that of the original version shown in Figure 18.22a. It is now even closer to the performance of the Auratone 5C, shown in (b), but it is slightly smoother and has more extended bass. The loudspeaker in (c) has a basic similarity, but the midfrequency emphasis is moderated. It is lower in amplitude and slightly lower in frequency. The loudspeaker in (d) also has an underlying midfrequency emphasis but adds some high-Q resonances around 600 Hz and 2.5 kHz that add an annoying "personality" to the playback. Why? (e) shows a loudspeaker that seems to be trying to be flat but fails at both frequency extremes: "punchy" bass due to the 80–100 Hz, underdamped woofer bump, and rolled-off high frequencies. The fact that all of these monitors, some more than others, exhibit high-frequency roll-off is puzzling in an age when arguments are being made that bandwidth beyond 20 kHz is a necessity for monitoring.

Manual from the manufacturer

It's a legendary studio monitor, literally. The policy of designing NS10M is quite different from today's perspective. The loudspeakers intended to achieve flat response on not on-axis but sound power. Thus, without further equalization, NS10M might sounds too bright and forwarding under today's room treatments. Due to this characteristic, NS10M is used for checking vocal details in mixing.

Source: Toole, F. (2012). Sound reproduction: The acoustics and psychoacoustics of loudspeakers and rooms. Focal Press. http://www.embedded.com/print/4214420 (Excerpt for Chapter 18.5.)

Mackie HR824

Pretty low distortion in bass is impressive. Directivity pattern is also excellent. Very linear free field response  on 50-20000Hz range. Without any doubt, these loudspeakers are very credible equipment not only for studio monitoring but also for serious music listening.

Source: http://www.gearslutz.com/board/so-much-gear-so-little-time/514514-berhinger-truth-b3030a-monitors-2.html

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