Subwoofer Reviews

Because the XTR-SSA3 and XTR-BP20 can be placed on tables or stands or mounted directly on a wall, I had to make a decision about which measurement to focus on. I ended up measuring the speakers freestanding, atop a 2-meter-high stand with the measurement microphone at a distance of 2 meters from the fronts of the speakers. I then attached each speaker to an ersatz “wall,” a special measurement stand I made using a 2 x 4-foot panel with foam around its edges to simulate the effects of mounting the speaker on a long wall.

The curve presented for the XTR-SSA3 soundbar represents an averaged frequency response from 0° to 30°, smoothed to 1/12th of an octave, with the mike aligned with the center tweeter driver and only the center channel driven. Because the XTR-BP20 surround is intended to deliver diffuse, rather than direct, sound, I got its frequency response by averaging measurements from 0° to 60°. To get the bass measurements, I close-miked the woofers, then spliced those to the averaged response curves at 300 Hz.  I measured the response of the SuperCube 4000 using ground-plane technique, with the sub sitting on the ground and the mike positioned 2 meters away.

The XTR-SSA3 soundbar has a fairly pronounced treble rolloff above 16 kHz that mars its response out to 20 kHz, but it’s extremely flat in the region that really counts (i.e., 300 Hz to 10 kHz). There’s a broad dip between 1 and 4 kHz, maxing out at about –4 dB, but in general the response is impressively smooth. Further off-axis, at 45° and 60°, big dips of 15 to 20 dB occur between 1 and 3 kHz, which is the result of interference between the woofers. There’s not much bass output below 150 Hz.Although the left and right speakers of the soundbar aren’t supposed to have flat response because of the shaping produced by Definitive’s Spatial Array interaural crosstalk circuit, just for kicks I ran a measurement of the left driver with the microphone positioned directly in front of the driver and 2 meters away, and only fed the left channel with a signal. The effects of intentional interference between the left- and right-channel drivers are evident, because the response shows severe peaks and dips above 1 kHz, and a measurement of ±12 dB from 160 Hz to 20 kHz.

The XTR-BP20’s response is way down in the treble because I included the response out to ±60° off-axis in the average. However, it, like the soundbar, delivers very smooth response from 300 Hz to 10 kHz.

As expected, wall-mounting these speakers changes their frequency response some. With the soundbar, wall-mounting introduced a dip between 650 Hz and 1.2 kHz, max 8.7 dB at 770 Hz. With the surround, the dip was more extreme, maxing out at 15.1 dB at 750 Hz and spanning 520 to 930 Hz. There were only minor changes, less than ±2 dB, at higher frequencies.

Impedance (see chart) for all of these speakers runs rather low. For the soundbar’s center channel, it drops to 3.3 ohms at 420 Hz with a phase angle of –9°. For the soundbar’s left/right channels, it drops to 3.2 ohms at 1.44 kHz and +3°. For the surround, it’s 3.6 ohms/480 Hz/–11°. As you can see in the chart, impedance runs fairly low for all of these measurements throughout the audio band, so I don’t recommend use of these speakers with a super-cheap (i.e., less than $300) A/V receiver.

Sensitivity of these speakers is low: a little over 78 dB for the soundbar and 81 dB for the surround. Wall-mounting the speakers improves their sensitivity by 3 to 4 dB above 1.5 kHz. Definitive rates the soundbar’s sensitivity at 90 dB but doesn’t specify the measurement method. My method averages quasi-anechoic output from 300 Hz to 10 kHz, which is similar to A-weighting. I also tried an in-room measurement using pink noise with A- and C-weighting. The best result I was able to get was 87 dB with the speaker wall-mounted and the meter set for C-weighting.

The subwoofer measures admirably flat with EQ defeated (see chart). EQ1 mode introduces a 9.6-dB peak centered at 40 Hz. EQ2 mode creates a milder, broader 5.2-dB peak centered at 54 Hz. EQ3 is similar to EQ2, but with a sharper, 11.3-dB peak. EQ4 pumps up the energy between 50 and 100 Hz by 7.7 dB on average. Combined low-pass function of the subwoofer’s crossover and driver is –23 dB/octave.

The SuperCube 4000 seems to be tuned for maximum punch at 50 Hz. Unusually, it has 5.6 dB higher max output at 50 Hz than at 63 Hz. For a sub this size, max output is very good in the low bass (40-63 Hz). While there’s still measurable output at 20 Hz (something very rare for a sub this small), it declines sharply below 31.5 Hz. These measurements were taken with the EQ bypassed. —B.B.