Bookshelf Speaker Reviews

Bottom Line

The AT-2 gives me just what I’d always hoped H-PAS could deliver since I first heard about it a few years ago: powerful, deep bass from a small speaker. And the rest of the audio range sounds really good, too. At $1,800 per pair, it’s expensive for a little speaker. But of course, there are lots of high-end mini-monitors that sell for two or three times that, and I bet none of them can match the AT-2’s bass performance.

Extended Test Bench

Measurements

Frequency response
37 Hz to 20 kHz ±3.0 dB (on-axis)
37 Hz to 10 kHz ±2.9 dB (±30°)
37 Hz to 20 kHz ±4.9 dB (±30°)

Sensitivity (SPL at 1 meter/1 watt)
87.1 dB

Impedance (minimum/nominal)
5.4/8 ohms

Bass output (CEA-2010 standard)
• Ultra-low bass (20-31.5 Hz) average: NA
20 Hz, NA
25 Hz, NA
31.5 Hz, 82.3 dB
• Low bass (40-63 Hz) average: 109.0 dB
40 Hz, 104.7 dB
50 Hz, 110.4 dB
63 Hz, 110.7 dB

I measured the AT-2 with the microphone placed at a distance of 2 meters, with the speaker atop a 2-meter-high stand, using quasi-anechoic technique to remove the effects of reflections from nearby objects. Bass response was measured using ground plane technique, then smoothed to 1/3rd octave and spliced to the quasi-anechoic curves at 300 Hz. The curves you see in the accompanying chart show the on-axis response (blue trace) and the average of measurements at 0°, ±10°, ±20°, and ±30°, smoothed to 1/12th octave. All frequency response measurements were made with a Clio FW audio analyzer then imported into a LinearX LMS analyzer for post-processing.

The measurements of the AT-2 are very good. The off-axis ±30° averaged measurement to 20 kHz suffers a bit because of some roll-off above 16 kHz, but this probably won’t be audible to most listeners. Further off-axis, you get just a textbook treble roll-off with no anomalies in the midrange. These measurements were taken with the grille off. The grille has a small effect on the on-axis frequency response, reducing output between 6 and 7 kHz by max -1.3 dB and boosting output between 9.5 and 11.5 kHz by max +2.1 dB. The tweeter level switch affects frequencies above 6 kHz, boosting by +1.5 dB or cutting by -1.1 dB.

And of course, it’s worth noting that the bass response goes down to 37 Hz.

Impedance measurements (also performed with Clio FW) show that the AT-2 is easy to drive. Minimum impedance is 5.4 ohms at 140 Hz with a phase angle of -6°. The tweeter level switch changes the impedance slightly; in the tweeter + position, the minimum is 4.8 ohms above 10 kHz with a phase angle of -3°. Given the speaker’s average sensitivity from 300 Hz to 10 kHz of 87.1 dB (2.83 volts/1 meter), you can hook this speaker up to any receiver and get reasonably loud levels from it.

I measured the AT-2’s bass output using CEA-2010 methodology — something I don’t normally do with a bookshelf speaker, but given Atlantic’s claims about H-PAS I thought it appropriate. Measurements were taken at 2 meters then scaled up +6 dB per CEA-2010 requirements so that they are equivalent to 1-meter results. I connected the speaker to a Krell S-300i integrated amp. Because the speaker won’t benefit from boundary reinforcement (i.e., it probably won’t be placed directly against a wall), I measured it atop a 30-inch stand. Results this way were -1 to -2 dB lower than placing the AT-2 on the ground.

Output is comparable to that of a typical 8-inch subwoofer in the low bass (40-63 Hz) octave, at 109.0 dB (averaged in pascals). That’s only about -3 dB below the Velodyne EQ-Max 8 subwoofer — and remember, using two of the AT-2s should give you about +6 dB more bass ouptut. There’s not enough output below 40 Hz to let me calculate an ultra-low bass (20-31.5 Hz) average. Note that these measurements are not comparable to those I made of the AT-1. Those measurements were made using our old 10% THD standard, and CEA-2010 is more forgiving.