Velodyne DD-18 Inside Look

    

Figures 4a – c: Inside the DD-18 (Left): System disassembled, meter stick & 12” ruler included for scale; Middle: Looking forward from back of cabinet toward inside of faceplate.  Note XLR jack sealed in silicon to eliminate wind noise. (Any hardware found in the amplifier - or anywhere else in the cabinet - that could provide a path for air leakage was sealed). Light gray band seen in driver aperture is the gasket. Dark lead seen at lower-right of the photograph supplies faceplate indicator light with current. Right: looking back at cabinet back panel and system amplifier, Note use of glue blocks throughout. 

Removing the grill cover, black gloss-finish fascia and driver revealed a moderately damped, well sealed cabinet built up of 1” (2.54 cm) panels. Glue blocks were used throughout. No cross bracing of any kind was used in construction of the cabinet. Driver and fascia held in place using Allan-bolt/t-nut mounting hardware. Both driver & amplifier openings are gasketed. The system rests upon 4 ¼-20 threaded aluminum feet with rubber inserts. They work very well in making sure the unit stays put.

The driver used in the DD-18 is certainly an heroic looking device!  Features include a Kevlar-reinforced cone with a 15.2” (38.6 cm) effective radiating diameter, variable-thickness EPDM surround, 1.25” (3.18 cm) (peak-to-peak linear excursion (1.75” (4.45 cm)(on transients), tandem, 3” (7.62 cm) wide, 6” (15.24 cm) long, push-pull voice coil, wound on a woven glass/polyamide resin former, a 24lb (10.89 kgs) magnet structure and a die cast aluminum basket.

   

 

Figures 5a –c Bottom right: DD-18 Driver with 1’ ruler included for scale; Top left & right: driver and voice coil. Bottom left: close up of motor assembly. At left in image: power leads encased in surgical tubing. Image center: bottom of drivers two linen spiders showing.  At right of image: Accelerometer leads. Velodyne doesn’t attempt to make their drivers pretty for press photo shots.  You won’t find any chrome or gold finish, just a raw, high performance driver. But then again, beauty is in the eye of the beholder.

Figures 6a,b: Left: DD-18 Accelerometer (left end attached to driver). Right: Accelerometer & lead seen at right. Note holes in the bottom, left-hand side of cone.

Yet another interesting feature of the DD-18’s driver are the clusters of small holes seen at the bottom of the cone in Figure 6b. Purpose? Velodyne’s design intent can be found in the Description of the Preferred Embodiment section of US Patent #4,727,584 “Loudspeaker with Motional Feedback”:

“The function of the hole clusters 38 is to control the speed of waves propagating radially outward of the cone, so as to provide that the speed varies to some extent with the radial angle. That is, the propagation speed in the sectors containing a cluster of holes will be different from an adjoining sector not containing such a cluster. Sonic waves resonate at a slightly higher frequency between the hole clusters than through the clusters. The consequence of such an arrangement is that a somewhat “jumbled” pattern of sound waves is created, which apparently combine in a fashion to prevent marked resonance effects leading to instability.”

The Amp & Digital Drive: The Virtuous Cycle

 

 Figures 7a,b: (Left) DD-18 Amp. Note array of jacks at left running top to bottom, sealed to prevent air leakage. (Right) DD-18 control panel, recessed & gasketed, bolted into back of cabinet. Provides data, audio & video interconnects along with On/Off switch and volume control.

Digital Drive is an impressively comprehensive subwoofer control system. It encompasses digital implementations of all crossover, filter, phase, contour functions as well high-gain servo control (featuring accelerometer A-D sample rates up to 15.8k) and all linked into an extremely efficient Class D power amp.

Interaction with the system is via a remote (supplied with batteries!) and user-supplied video display capable of handling either S-video or composite video signals.

System feature highlights include:

• On Screen Display presenting a total systems control interface
• 8 – Band parametric EQ, with level, frequency & Q control parameters, of course.
• Low-pass crossover filter
• Subsonic filter
• Phase control
• Polarity control
• 6 Listening-mode Presets (4 factory set, 1 user customizable and EQ Defeat)
• Contour EQ (Freq. & Level adjustable) for each preset
• Master system volume control & individual Presets volume control
• Servo loop gain control (1: lowest loop gain – 8: maximum loop gain)
• Night mode option
• RS-232 Input
• System Firmware is user-updateable
• System capable of managing daisy-chained subs.

Figure 8: Introductory Screen.

Power up the DD-18 and the introductory screen is what your OSD greets you with. It presents basic operational information such as Firmware version, Model ID, sub volume and whichever default preset has been selected.

Punch “Menu” then “12345” on the remote and you’re taken to the System Response\PEQ Screen (Figure 9). Here, the system indicates the volume is at 30, manual mode is in effect and the response is flat lining as the supplied setup mic was not connected to the system when the screen capture was done.

Setting equalization can be fully automatic, fully manual or a combination of the two, letting, the DD-18 run the equalization set up automatically, then manually tweaking the results. The system monitors the process and its effects on the resulting dB spl curves via the supplied mic. Being able to watch changes in DD 18’s amplitude response due to changes made at the PEQ is as useful as it is efficient.
 

Figure 9: System Response\PEQ Screen

  

Figures 10a, b: Mic w\ 1’ ruler for scale, Mic kit with accessories

Figures 10a & b show the included mic along with various included accessories, such as the tabletop mic stand, mic clip for stand mount, 20’ XLR to XLR mic cable, windscreen, and carrying case. Also included but not shown are a 25’ video cable and 25’ audio cable.