OK, so how does this Digital Drive subwoofer sound? In a word, fabulous. I like to have maximum servo-feedback, so I set up a Preset with the maximum (8). The entire house shook with this subwoofer, but the overall response was so much more natural than it used to be with no EQ in the system. It worked with my other subwoofers, even though they are older models with no EQ.
Since I use a digital projector with component video, I simply switched to S-Video in order to make any adjustments in volume or other parameters on the DD18, then back to the movie on component video.
Moving the servo-feedback to a lower setting produced more of a boomy sound that some people like, but I do not. (The boominess is a manifestation of more harmonic distortion.) So, regardless of the other parameters, I would use servo-feedback set at 8 for all Presets.
In practice, I measured SPLs at about 95 dB - 100 dB when watching some of my favorite action films that have crash, bang, boom galore.
On the Bench
I made these measurements using Presets that let me compare THD with minimum servo-feedback (Theater/Music setting 1) and maximum servo-feedback (Theater/Music setting 8). The measurement microphone was placed 4" from the front of the driver. For maximum SPL measurements, the microphone was 18" from the front of the driver.
At 15 Hz and 100 dB, and servo setting 1, THD was 4%. Maximum SPL was 100 dB.
With the servo setting at 8, THD dropped to 3%. So, the servo does its job.
At 20 Hz, maximum SPL was 103 dB, and THD was less than 2.5% with servo setting 1.
Servo setting 8 reduced THD to less than 2% at 20Hz.
At 25 Hz, maximum SPL was 110 dB. Servo setting 1 gave a THD at just less than 2%.
THD was reduced to slightly more than 1.5% with servo setting 8, at 25 Hz. These are all very good performance results regardless of the servo setting.
At 31.5 Hz, maximum SPL was 117 dB. This is really room shaking volume, and distortion was at 1.24% at 100 dB, and servo setting 8. At this, and other higher frequencies, I did not find significant differences in the amount of THD with respect to the particular servo setting.
I obtained 120 dB maximum SPL at 40 Hz. THD at 100 dB was less than 1%.
THD was less than 0.75%, using servo setting 8, and 100 dB at 50 Hz. Maximum SPL was 122 dB.
At 100 Hz, maximum SPL was 123 dB. THD was 0.57%.
The MLS quasi-anechoic frequency response is shown below. Remember that MLS is a very unflattering way to look at bass response, and the measured room response shown in Part I is ample evidence of how important the room is to getting plenty of bass. The addition of digital EQ shows how flat you can actually get the response when applied. The impulse response shows an initial negative swing, followed by a positive one. This is easily remedied by changing the polarity in the system settings menu, but all variations should be tried in the listening, since the subwoofer is in a different position than the other speakers.
Velodyne's new Digital Drive series is a huge advance in subwoofer technology. You only need one to work with several subwoofers, and it corrects the biggest problem we have in low frequencies for our home theaters, those dips and peaks.
Even if you are not in the market for a subwoofer, you need to hear this new technology so you know what can be had, when you do get around to planning for that new sub.
We are awarding Velodyne our Best of 2003 for Subwoofer Technology. Congratulations to a fine company!