Velodyne Digital Drive Plus 18 (DD18+) Subwoofer Introduction
Velodyne has a long and storied history in the commercial subwoofer market and after more than 25 years has solidified itself as one of the most recognizable names in high end audio with their inovative technological advancements and commitment to pure sound reproduction. The subject of this review is their top model in the Digital Drive Plus line the DD18+ which packs an 18” driver, a 1250 watt rated amplifier and a large amount of DSP and electronics control. This unit represents the continued refinement of Velodyne’s top subwoofer platform and follows the familiar Velodyne formula for success: Active servo control, sealed enclosure, well engineered driver, powerful amplifier and flexible built in DSP processing housed in a reasonably sized and attractive package.
Unpacking and Initial Thoughts
The DD18+ is delivered by freight in a very large box and tips the scales at over 160lbs as delivered so it is a two person affair for most. Still unpacking was fairly easy and uninvolved. The DD18+ is double boxed and additionally has cardboard corner reinforcements. Inside of the inner box is a large top and bottom foam insert that fits over the DD18+ and houses the accessory pack. The DD18+ is also contained within a large cloth bag which is additionally inside of a large plastic bag with a small silica pack to combat moisture. Inside of the accessory box is: the measurement microphone in its own plastic snap case, the user manual, remote control, 2 discs containing the software to connect your TV or computer to the DD18+ and the audio track for measuring the response, a variety of cables for connecting the microphone, computer, television, etc and a pair of white gloves.
Note to Velodyne. Please include 2 pairs of gloves! How many new owners will move and position $4,999, 140lb subwoofers solo? Without a second pair of gloves the person gracious enough to help move the sub will be white glove-less, thus polluting the fine exterior of their shiny new subwoofer with their dirty mitts. That defeats the purpose of having the white gloves in the first place.
Initial thoughts after getting the DD18+ unpacked and looking through the accessory pack contents for a few moments? This is a very high quality unit here, man that is a nice finish and finally…Where to begin? The DD18+ came in the black gloss ebony finish that was really pleasing to my eyes. That particular finish is very dark and mirror polished, but you could still see wood grain underneath on close inspection. Everything about the DD18+ was constructed well, solid feeling and the curved side panels give it a streamlined appearance. The DD18+ is a good sized subwoofer that is not going to disappear easily, but it does have a very classy and high tech look to it. It reminded me of something that you would see at Bruce Wayne’s place.
The Velodyne DD18+ design utilizes an 18” driver in a sealed enclosure with a 1250 watt amplifier and includes a remote control for adjustment of output or EQ presets to suit your tastes without even having to leave your seat. This is already a recipe for quite the subwoofer, but the DD18+ doesn’t stop there and also utilizes Velodyne’s trademark active servo control which uses an accelerometer to monitor the voice coil position and provide adjustment to correct the output of the system and lower distortion. Velodyne claims this happens over 3000 times per second and the result is less than 1% THD during typical use. The DD18+ also houses a powerful DSP system which allows it to connect to a computer, measure and EQ its own response, or modify and save user presets for recall later. The DD18+ may also EQ itself with no need for connection to a display if there is none available to connect it to.
Usually I would have removed the driver for pictures and inspection, but I did not remove the DD18+ driver due to it being a rather involved affair including removing the amplifier, disconnecting the driver and servo sensor from the amplifier, unbolting the driver motor from the enclosure bracing internally, removing the grill and front fascia, removing all of the driver bolts, etc. I contented myself with inspecting the driver while it was still attached to and housed in the enclosure. Needless to say it is a high quality and robust unit. The motor is very large and heavy. It looks to be built on 2 roughly 9” diameter ceramic slugs and a very large and tall top plate. There is also a roughly 1” pole vent with a screen to catch debris before they enter the gap. The driver uses a 3” nominal voice coil in what appears to be an underhung arrangement where the voice coil is short and the top plate and magnetic gap are tall. This is a way to improve driver linearity with stroke by keeping the motor force more constant with respect to voice coil position and thus reduce harmonic distortion. The cast aluminum frame used is sturdy and well ventilated. The cone is light but stiff and strong. I am a fan of Rohacell composite cones for this reason, not to mention that they also happen to look great. The spiders are generous in size and the surround is as well suggesting that the driver is capable of plenty of stroke for demanding low bass transients. This is a very high quality driver.
The amplifier itself appears to be of similar high quality and connects to the front panel control unit via a ribbon cable. Six large reserve capacitors were in evidence on the top circuit board as was a small aluminum heat sink which indicates that this is the power section. Another larger circuit board is mounted below the power section. During testing and use the amplifier face never got much more than warm to the touch implying that it is a very efficient design. Also the amplifier contains a simply staggering amount of input and output connection possibilities. Everything from balanced XLR ins and outs, to 12v trigger, to speaker level inputs, unbalanced RCA, serial ports and even an Ethernet port. There is even a USB port on the front panel. No one can accuse Velodyne of limiting your options that is for sure.
The enclosure of the DD18+ under review was a beautiful ebony gloss black finish in which you could still see wood grain if looking closely. Internally the enclosure has a very large window brace in the center which the driver motor is also anchored to with bolts. This ties every major panel of the enclosure together except for the back panel which houses the amplifier. There is also a generous amount of poly fill stuffing inside of the enclosure behind the driver and on the walls. During testing and use I noted no cabinet resonances or audible issues related to the cabinet even at the loudest drive levels. It is very solid and inert.
Long time, no speak.
By way of comparison, my own test rig is capable of 1.943V RMS in -10dBV trim and 7.62V RMS in +4dBU trim via the Lynx 2B sound card. Havng tested more Velodyne subs than most, and using them in my own home system, I am all too aware of the potential for overloading them inadvertently.
The gain structure on the Velodyne DD subs is rather high, particularly when driven via the XLR inputs, and the overload threshold is not very generous. By my own measurements, a form of clipping sets in around 1.5V RMS. The odd thing is this distortion starts to creep in below 20Hz to start with. As you increase the drive level by a few dB, the distortion creeps up the frequency scale maintaining a very definite descending slope with increasing frequency. Which suggests to me this is not simple clipping but possibly some quirk in the DSP code at high amplitudes. I have a question about this open with Chris Hagen at Velodyne currently.
The upshot of this is that I am acutely aware of the potential for overload when testing these subs. The sloping nature of the distortion as it starts to appear makes it less easy to spot in swept sine tests as it simply becomes a contributing factor in the background. Spotting it with tone-burst testing would be even harder as it will typically just appear as rather high levels of odd-order distortion. Something for the reviewer/tester to beware of is all I am saying.
However, this issue can also impact on the general user. By their nature these subs will tend to end up in high-end systems, often partnered by equipment that generates signal levels more typical in the professional arena. For example, my own Theta Casablanca DACs are specified to deliver up to 20V RMS via XLR. If you connect a DD sub direct to this and match levels, you typically end up with the DD volume set to something like 3 to compensate for the very high signal level from the processor. In this scenario, it then becomes rather easy to clip the subwoofer on loud material, which is a pity after spending all that money! A higher overload margin and lower gain on these subs would be a good idea, particularly via the XLR inputs.
My advice to anyone using these subs in such a high end system would be to ensure you don't set the DD volume lower than 15 and match the speaker levels by dropping the level of the subwoofer output in the processor setup menus only. If you currently have the DD volume set in single figures, then this overload issue may be a problem for you that you may not even be aware of.
I've been meaning to update this thread for some time and just never got around to it.
To recap, for all Velodyne Digital Drive Plus sub owners, regardless of sub size, there are three sets of inputs on each sub. One set for speaker level inputs, one set for single-ended line level, and one set for XLR line level. The speaker-level inputs and the single-ended inputs have dedicated input level controls, so input stage overload is not a factor, but the XLR inputs do not have level controls.
For those of us driving the DD Plus subs with full-range balanced outputs from our pre-amps, input overload is a very real factor. As cjwhitehouse noted, many owners running XLR cables are using sub volume levels of "5" to "10", when Velodyne ships the sub with a default of "30". I called Velodyne and asked if there was an XLR input sensitivity fix, and they never responded.
Some time ago it occurred to me that the fix was simple - use XLR line level attenuators ahead of the XLR inputs on the sub. Fixed levels (-10db, -20db, etc.) are available from Parts Express for about $10 each, and Audio Technica makes some more expensive adjustable ones. I tried the -10db versions from Parts Express.
What a difference! I remember that first listening session with the attenuators in-line clearly, and it was several months ago. Prior to the attenuators I was running the DD18 Plus's volume control at "8", and now I use "25". So what? Well, two things changed. First, the granularity of volume adjustment is so much finer. Before, "7" was too little and "9" sounded bass-heavy. Now I can fine tune the bass level depending on the recording from "20" to "30" and the subtlety of effect is very nice. Second, the sub's EQ is more effective and appears to be more accurate when I do in-room measurements. I don't know for sure that input overload was causing the problem, but the attenuators made a significant, easily audible and measurable improvement in the sub's usability and EQ performance.
As I said, most users won't care because they'll probably use the single-ended inputs. But if you are using the XLR inputs on Digital Drive Plus subs with full-range pre-amp outputs I highly recommend trying XLR attenuators.
Please look at the distortion chart.
Isn't that too close to the amp when bolted/screwed on? If the amp is hot wouldn't the foam catch on fire? Or is it made out of fireproof material?
Ahhh gain structure...There is a surprising amount of final system performance tied to this and many are unaware of how much.
Maybe AH should write up a dummies guide to setting gain structure? I recall starting a thread about it over at AVS and never coming to a conclusion (at one point an expensive o-scope was required and then building some sort of attenuation circuit instead of the o-scope to use on my Mobile-Pre/REW setup to test for signal distortion as a VMM couldn't do this). Mind you, that was probably more involved as it included an outboard amp and DCX..
Just got too complicated. :o