Revel Ultima Sub 30 powered subwoofer Page 2

Initial adjustments included channel identification and phase checks using the Stereophile Test CD (STPH002-2). The phase test revealed that my system's phase response was reversed with the Sub 30 connected and its Phase control set to 0 degrees. Yet this control affects only the subwoofer output, not that of the main speakers.

Next I used the Revel Low-Frequency Optimizer Test Signal CD, which Revel includes with the sub, and a RadioShack 33-2050 analog sound-level meter to measure the Sub 30's in-room response. To analyze the results in order to properly set the controls of the Sub 30's three parametric equalizers, I downloaded the Revel Low-Frequency Optimizer Software, v., from the Revel website, and ran it on my IBM laptop.

The LFO Test Signal CD provided test signals and Kevin Voecks' clearly enunciated instructions. The signals allowed me to set the levels of the main speakers (bandpass-filtered pink noise, 500Hz-2kHz) and subwoofer (bandpass-filtered pink noise, 20-80Hz); an 80Hz warble tone helped me set the phase. I determined that the Sub 30's level should be set to "2," the low- and high-pass crossover points to 80Hz, and the phase to 180 degrees.

The LFO CD also provided tracks containing 23 warble tones between 20Hz and 100Hz (1/12 octave, 3Hz modulation frequency, -20dB RMS average). I set the RadioShack meter to its 80dB scale, C weighting, and Slow mode. (The LFO software automatically compensates for systemic errors in the RadioShak SPL meter.) Standing at my listening chair—sitting would have blocked the meter, which I'd placed on the chair back at my ear level, 37" from the floor—I keyed each SPL meter reading into the laptop running the LFO software. Once these data had been entered, I clicked on the Analyze radio button in the LFO program. The program generated a complex frequency-response graph, along with recommended settings for me to enter via the rear-panel equalizer controls to correct for my room's anomalies.

Although the owner's manual has many clear diagrams, as well as a full explanation of most of the Sub 30's controls, no written instructions for setting the filter frequencies, selecting their slopes, or conducting the room-calibration procedure are supplied with the subwoofer. Rather, the calibration instructions are given on a series of startup screens in the LFO program. It would have been more helpful to have these instructions written in the manual, and to have included in the shipping carton the LFO software and the test signals. Perhaps the LFO software has been targeted for system installers. Those wishing to install a Sub 30 themselves can download the software from the Revel Ultima Sub 15 section of the Revel website.

Although this calibration procedure can be done from the listening position, Revel's software does not permit adjustment of the Sub 30 with a remote control. All changes in the level, phase, and equalizer settings had to be done manually, as I shuttled back and forth between my listening chair, where sat my meter and laptop running the LFO software, and the room corner, where sat the Sub 30. This is much more tedious than the calibration routine for the Velodyne DD-18 subwoofer (reviewed in June 2004), which can be done from the comfort of the listening chair.

However, setting the nonparametric equalizer, which must be done by trial and error with the Velodyne, are determined automatically by Revel's LFO software. Voecks suggests that it would be more tedious, and perhaps impossible, to get the Sub 30's equalizer settings correct through trial and error. The Velodyne DD-18 subwoofer's built-in signal generator, microphone, and virtual spectrum analyzer sure were helpful in verifying Revel's room-calibration approach. (See p.133 of the June 2004 Stereophile.)

I set up the Velodyne's calibration microphone on the back of my listening chair at my ear level, and set the DD-18's volume control to "0" so that it would put out no audio signal. I then keyed the Velodyne's remote to display its internal System Response screen on my TV monitor. This automatically initiates a repeated sweep tone from the DD-18's signal generator, which is then fed into a tape input of my preamplifier. First, I drove the Quad ESL-989s alone without the subwoofer (fig.1, note that this and the following graphs cover the 20-200Hz region). The Quad's frequency response showed a dip at 60Hz and peaks at 70 and 40Hz, the response falling off 10dB by 35Hz.

Fig.1 Quad ESL-989, no subwoofer, in-room response (25dB vertical range).

Next, I added the Sub 30 with the equalizer shut off (fig.2). The LFO analyzed the results of the 23 in-room response readings to determine settings for the three equalizers: 30Hz (-4dB), 43Hz (-9dB), and 59Hz (+2dB). The new settings produced a flatter (±4dB) room response (fig.3), shown by the removal of the 40Hz peak seen in the nonequalized system response (fig.2). With music, the resulting bass response was significantly more powerful and involving with the parametric equalizer active. (The final LFO screen is shown in fig.4).

Fig.2 Quad ESL-989 with Revel Ultima Sub 30, no equalization (25dB vertical range).

Fig.3 Quad ESL-989 with Revel Ultima Sub 30, equalized for flattest in-room response (25dB vertical range).

Fig.4 Revel Low Frequency Optimizer screen for Quad ESL-989 with Revel Ultima Sub 30 in LG's listening room.

Once correctly level-matched and equalized, the Revel Ultima Sub 30 generated extremely deep bass. It delivered dynamics with suddenness and impact, which added to the musicality and realism of the deepest notes. More important, it did not change the pitch, timbre, or quality of midrange timbres. The Revel's low-pass filter effectively suppressed any upper harmonics in its output, something that other powered subwoofers have been unable to do in my large listening room. The Revel blended well with my Quad ESL-989s, producing a seamless integration of bass and midbass. The midbass emphasis common among woofers in full-range speakers was totally absent from the Sub 30, rendering a cleaner, better-defined impression of the midbass and above.

Harman Specialty Group
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Bedford, MA 01730-1413
(781) 280-0300