|Velodyne Digital Drive Series DD-12 Subwoofer|
|Home Theater Loudspeakers Subwoofers|
|Written by Christopher Zell, Ph.D.|
|Thursday, 01 April 2004|
Page 1 of 3
The advent of home theater systems and, to some extent, the increased popularity of small monitor loudspeakers has resulted in a boom in manufacturers offering wide varieties of subwoofers. Until recently, only a relative handful of manufacturers produced true subwoofers, and even fewer offered truly high quality. Velodyne has been a constant force in this arena, continually producing some of the most revered subwoofers on the market at any given time. Their recent HGS series of relatively diminutive subwoofers is no exception, generally considered among the cream of the crop despite fierce competition. The HGS series offered high output SPL capability as well as exceptionally low distortion, especially when compared to most of its competitors. So it was a challenge for Velodyne to achieve a substantial step up in performance from this series. The challenge was answered by the new Digital Drive series, offering lower distortion via their trademark servo control, and increased volume capability, while adding in the ability to tune the subwoofer to the room with an array of sophisticated software and hardware tools. Similar to the HGS series, there are four models in the Velodyne’s Digital Drive line, the DD-10, DD-12, DD-15 and DD18, the numerals signifying the diameter of the driver cone. During the last few months, I had the opportunity to audition the Digital Drive DD-12 subwoofer, which has a suggested retail price of $2,999.
Normally, large ugly boxes come to mind when the subject of subwoofers comes up. The DD-12 is neither, coming in an extremely classy, attractive and remarkably compact package. At first glance, the enclosure seemed so small that I was certain they had sent me the smaller 10-inch model by mistake, until I verified via the back panel that indeed the DD-12 was sitting in front of me, and noted the substantial but not back-breaking 67-pound weight. Measuring a mere 14 inches high by 14 inches wide by 15 inches deep, it could fit almost hidden behind my Revel Voice center channel, being only a bit wider than the stand’s bass. The glossy black top and sides with rounded corners were especially attractive and well suited to match cosmetically with my reference gloss black and black ash Revel Ultima loudspeakers. The front panel has a black cloth grille covering the 12-inch driver, with a lighted blue logo and red underlined late-night-mode monitor highlight completing the understated but elegant cosmetics. The logo can be turned off to allow the DD-12 to disappear in a darkened home theater. There are a plethora of connections available on the DD-12 rear panel, starting with single-ended RCA inputs and speaker level inputs, as well as a balanced XLR signal connector. Multiple DD-12 subwoofers can be daisy-chained via a pair of RCA output pass through connectors. Additionally, the subwoofer incorporates a pair of a fixed 80 Hertz, 6dB/octave high pass filtered outputs that can be used for systems requiring a crossover for main loudspeakers. A pair of serial ports are provided, one for communication to a computer or touch panel remote, and the second to interface to additional daisy-chained subwoofers. A remote sensor plug connects to an optional infra-red remote control receiver, allowing remote control of power, volume and mute functions for out-of-the way subwoofer installations. The DD-12 comes equipped with a microphone that plugs into a rear XLR input. Additionally, RCA audio jacks send internal sweep signals to your control preamp or receiver to generate low-frequency test tones. S-Video and composite video outputs are provided to visually observe the Velodyne’s menu and measurement screens on your video monitor. There are no buttons or dials for controlling the DD-12 on the rear panel, save a pair of volume up/down pushbuttons located to the upper right. No need to worry, for this is an extremely flexible unit, which has only limited control via the back panel. This is left to the supplied remote control unit, a rare item when it comes to subwoofers. It is great to have access to subwoofer functionality from the listening seat, but be careful to not lose the remote, or you cannot change any settings other than volume.
Don’t be mistaken into thinking the Velodyne Digital Drive series are repackaged HGS subwoofers with added processing, as impressive as that would be in itself. The cabinet volume is significantly increased and the purported maximum driver travel is one-quarter of an inch greater. Combined with an improved switching amplifier and a new controller board, this generates 2.5dB added output for the DD-10 and DD-12, and around 4dB more for the 15- and 18-inch models. The cabinet volume increases are due to a slightly increased cabinet size, slightly thinner, but with fully braced walls and a more forward driver mounting configuration
Now for the fun stuff corresponding to the measurement and correction capabilities of the Digital Drive series. The DD-12 is a very unique subwoofer package, containing the aforementioned remote, a microphone and an XLR connector terminated cable. It also utilizes eight parametric filter channels, each with user variable level, center frequency and Q (bandwidth). I found the supplied cable to be a bit short for my room, causing me to drape it in a straight line over chairs and cabinets in order to position the microphone in my potential listening positions. For normal-sized rooms, it should reach most measuring positions, but I prefer a longer cable, allowing me to move the microphone all around the room, assessing low-end response as a function of microphone location. This is not a serious problem, since the existing cable can be easily and cheaply replaced with a longer one.
To configure the Velodyne DD-12, you need a long composite or S-Video cable, and a long stereo RCA interconnect. A three way cable with audio left and right and video comes furnished with the sub. Neither need be expensive audiophile types, since the video is only used to see the onscreen display, and the audio cable to send low-frequency sweeps signals to your AV preamp or receiver. These cables can be removed after calibration if desired, but if they do not create any physical hazard or visually impact your room, I recommend leaving them in place for future fine-tuning and adjusting. Two calibration screens are generated, one for adjusting filter parameters and displaying system real-time response, and a second for setting system settings. The top half of the system display screen is a live frequency response graph from 15 to 200 Hertz, with the bottom showing the icons for the eight parametric filters. The level, center frequency and Q (inversely proportional to filter bandwidth) of a selected filter is shown at the bottom right of the screen. All three parameters are user-adjustable, level from –12dB to +6dB in one dB steps, center frequency from 15 to 199 Hertz in one Hertz increments, and Q from 0.3 to 20. A digital servo system setting, labeled as the Theater/Music indicator, is also user-adjustable, with a setting of one for maximum theater (least amount of servo gain) and eight for maximum music (most amount of servo gain). The DD-12 outputs a continuous 15 to 200 Hertz sweep, which allows the user to immediately observe the effects of subwoofer placement or parametric equalizer settings. This real-time feedback is fun to observe, extremely informative and invaluable for assisting subwoofer integration. The system setting screen allows for a broad array of global and individual parameter settings for the six available presets. The parametric equalizer settings are global to all of the presets, with the exception of the sixth, which is an equalizer defeat. This bypass is extremely useful, enabling the user to quickly assess the effectiveness of various equalizer and correction settings.
Regardless of the fact that the DD-12 contains potential room and resonance correction filters, the first order of business, as with all subs, is to carefully move it around to achieve the most uniform response at the primary listening position. This is not normally an easy task, but the Velodyne software package is a great assistance tool. You will get much better results if you start out in the best possible subwoofer location before even attempting to adjust the available filters. You can literally move the DD-12 a few inches to a foot at a time and instantly see the dramatic effects in response and integration with the main speakers for frequencies under 200 Hertz. Indeed, upgrading to the DD-12 may be worth it just for the live frequency response made available through the internal bass response sweep, microphone and software. One key issue to note when optimizing the DD-12 is that you should be more concerned with severe dips rather than peaks. Boosting levels will not effectively increase cancellation dips, which are basically sonic black holes, but filter cuts can fairly effectively tame response peaks.
Once I decided on a potential subwoofer location, the first step in calibration was to measure the distance from the subwoofer to my listening chair, and update my preamp’s subwoofer distance/delay set-up parameters. Then I followed the generally effective and detailed user manual instructions to adjust the various tuning parameters. It was shocking and interesting to see how significant a sonic difference could be realized when filters were adjusted by only a dB or so at a time, or the filter Q changed by a small amount. A substantial benefit can be achieved by the patient user who is willing to iteratively make minute parameter changes to optimize the blending of the sub with the main speakers into a single, coherent source. The final curve may not be perfectly flat. Indeed, the room and available subwoofer locations will not likely allow a completely linear result, but the ability to optimize the filters and subwoofer parameters does let the user voice the subwoofer to application and/or taste.
One word of caution should be mentioned regarding overall amplitude settings during boost of final equalization. Adjusting the filters to achieve the absolute flattest overall response curve will not necessarily result in the best sound, even though it may look better graphically. Whether it is because music is not pure sweep tones, or because severe corrections may have a very adverse effect in locations outside of the calibration position, it is best to moderate any exaggerated equalization levels. Response holes are not effectively removed by boosts in the first place, so large gains will merely overwork the amplifier and driver unnecessarily. Even large resonances that tempt one to cut drastically may result in non-optimal sonics for music and movies. I adjusted the filters many times to create very flat response, noting that +/- 3dB over the entire bass region is actually very flat and difficult to obtain at times in a real world room, only to be disappointed after detecting some indeterminate anomalies while listening. I consistently found that when I went back and moderated filter settings, particularly those with the most drastic adjustments, the sound would improved dramatically, becoming more cohesive and coherent.