Training Day: Getting Inside V-DOSC Arrays
An intensive course going beyond supporting the product

By Chris Kathman


dV-DOSC cabinets on dV-SUB in the parking lot.

Sometimes there is a moment when theory suddenly, even shockingly, becomes reality. At the end of a three-day L-ACOUSTICS V-DOSC training, a bunch of us students were out in the parking lot in back of L-ACOUSTICS US, listening to a stack of three dV-DOSC cabinets sitting on top of a dV-SUB, blasting Steely Dan on a sunny afternoon. I didn’t think anything of it when I saw instructor Bernie Broderick walk toward the stack with one of the students.

I was standing about 100 feet away and the sun was setting behind them, so I could not quite see what they were doing. They seemed to be smiling and having a good time as they unhooked the rear pins, that were holding the top two cabinets at an angle that pointed them slightly upwards. Then, the two guys lifted the back of the cabinets and brought the front angle down until the sound was beaming directly at me.

The effect was literally mind-boggling ­ it was as though one moment I was walking down the street watching a neighbor calmly watering his lawn, and the next second the hose had been brought up and was spraying me right in the face with freezing cold water. V-DOSC really works, I understood in that startled moment, it really carries sound in an unusually focused fashion.

PRESETS AND PROCESSING

There has always been a fair amount of grumbling among sound companies about L-ACOUSTICS’ demands that purchasers use a given set of crossovers, along with approved amps, in order to generate a consistency of results worldwide. I remember years earlier when people complained about Meyer processors that did not allow the user to change crossover settings. Just as a mixer ­ and I hate to say this ­ but I really appreciate the ability to approach a set of Meyer or V-DOSC loudspeakers, anywhere in the world, and know that they are going to be approximately the same each time.


Preparing to attach three dV-DOSC to the already flown set of V-DOSC cabinets.

Bernie Broderick told me “L-ACOUSTICS locks the presets for some very good reasons. The mid and low sections of V-DOSC work under the limits of Wavefront Sculpture Technology criteria number two, which states that the acoustic centers of adjacent components must be less than 1/2 a wavelength of separation over the bandwidth of operation.

That means you need to set crossover points carefully so as to not decouple the adjacent components by selecting a crossover point that may be too high.

“This is critical at the crossover point between the mids and highs. There is very little margin for error in this region. If someone crosses the mid/high section any higher than what the preset has, they risk decoupling the entire mid section at frequencies higher then the factory set point.


Bernie and students attach the dV-DOSC to a dV-SUB cabinet.

“These presets are designed using spatial averaging and anything outside of personalized EQ could have negative effects on system performance. Personalized EQ is available on the inputs of the processor so anything that could need to be addressed should be addressed there. We believe that our factory settings are virtually unbeatable as a starting point and we are still tweaking them.”

It still seems hard to believe that it has not even been a decade since Jeffrey Cox received the initial demo boxes from France and began making his first sales. Not only have the sales of V-DOSC cabinets been quite successful in their own right, but another obvious indicator of their influence is the current prevalence of line array designs by most major speaker manufacturers, who were certainly not making any 10, or even five, years ago.

When I walked into Rat Sound to pick up a monitor rig for Cake in 1999, I remember seeing this row of smallish cabinets with soft covers on them and being told, yeah, this is V-DOSC, you hook ‘em together and they drive right up into the air like a little train.

When I attended the class, I learned that when the boxes are lined up on a stage under a chain motor, only the rear corners are pinned together, and then as each successive box goes up, the angle straps are attached on each side, which determine where the box is firing, in the vertical plane. As Bernie explained, one can just “bring the bumper up with a slight downward tilt, and gravity will close the boxes automatically ­ no lifting required.”


The completed array of both V-DOSC and dV-DOSC cabinets goes up in the air.

I asked Dave Rat why Rat Sound made the decision to buy a V-DOSC system. “It was the first internationally viable sound system that was not horn-loaded, line array or not. And based on the Rat system, which was a bass reflex system, we wanted to buy an off-the-shelf system that was similar to the Rat design.

“The goal for us was that we wanted to maintain the three major system designs, one of each. Those three designs are: compact horn-loaded (i.e. Nexo, d&b, Turbosound Flashlight), bass reflex arrayable (i.e. Rat Trap 5 or Clair Bros. S-4) and the line array.”

CHECKING OUT THE ANGLES

When I first saw the V-DOSC boxes, I knew nothing about Heil’s principles of directed sonic energy that defined his creation of an uninterrupted wavefront. The V-DOSC cabinets cannot exceed angles of 5.5 degrees from each other, but as Bernie explained to me, “dV-DOSC will open to 7.5 degrees. It’s based on WST criteria number one. The individual sources must account for at least 80 percent of the 100 percent virtual target.

Let’s say we have a 10-foot tall DOSC waveguide producing an isophasic wavefront. For this to work, the discrete wavefronts must be flat or isophasic. Curved wavefronts beyond a

1/4 wavelength at any frequency will create destructive interference.


Operation complete – here’s the finished ground stack.

"Obviously, this would be too cumbersome to move around, but it would be considered to have a 100 percent radiating factor. When you break it down into individual components, you start to subtract from the perfect 100 percent fill because you are now introducing gaps between discreet devices (wood, plastic, tilt angles, etc.).

If the total amount of gap between two sources exceeds 20 percent, you will break the continuous ribbon and will now have two independent sections. V-DOSC angles are limited to 5.5 degrees because that is the angular limit for 80 percent fill with that enclosure. The wood thickness plays a role in this as well by pushing the devices further apart.”

Bernie showed the class how to use the ARRAY2000 Excel spreadsheet to design systems that would cover a given area. We learned first how to draw a two-dimensional side view of a room, add mix positions and balconies, and eventually make the view three dimensional.

The modeling can show how V-DOSC or dV-DOSC cabinets impact the audience, and surfaces of the room, and the user then adjusts for even coverage by putting in different “virtual” angle straps.


Sharing the plans for “operation ground stack.”


A TRICKY QUESTION

His homework assignment of how to fly a large number of cabinets in a certain room was actually a trick question, and the correct answer was that it could not be safely done. Most of the class came in with that correct answer, that the rigging would be overloaded.

Bernie explained that if the student entered the data correctly, the result would be a series of “warning” messages that appear in ARRAY, telling the user that the given angle of hang, in relation to the weight of cabinets, is unsafe. He passed around a set of impressively jammed-up remnants of angle straps, from the actual system used in the homework example, that had been flown wrong, by someone who did not do a prediction beforehand. Although the rig did not come down, it seriously tweaked out the angle straps in their slots on the cabinets.

For the third and final day, Bernie took the class into the back of the

L-ACOUSTICS US warehouse and demonstrated how to properly rig cabinets and take them into the air on motors, as well as ground stacking them. The d-VFLIGHT cases for the smaller dV-DOSC cabinets allow them to ride in trays as a unit of three, and they can be landed that way, by unpinning the fronts and letting gravity be your friend, gradually lowering them down, and driving them off. He mentioned that the d-VFLIGHT cases “are considered by L-ACOUSTICS to be a ‘rigging accessory,’ not just a road case, and are essential for ease in setup and teardown.”


dV-DOSC resting in tray of dV-FLIGHT case.

Now, when I am mixing a band at a venue where there is a V-DOSC system, I can ask a sound company to show me the ARRAY prediction on their computer, and nod knowingly at how they chose the number of cabinets and how to angle them. I even know what an “axefixe” and a “balancier” are and how to pronounce them!

Bernie Broderick’s presentation was very thorough, very painstaking and no student was ever left behind. The atmosphere was very much one of the only dumb question being one that is left unasked, and on the ARRAY2000 and rigging days that I was there, Bernie was completely available to explain anything that someone did not completely understand.

It was an honor to watch the (mostly younger than me) attendees concentrate to digest the material, and then talk about their backgrounds and experiences during the breaks. It reminded me of the fact that working for a sound company is pretty much the same, no matter what region you are from, and the sense of community that Jeffrey Cox often talks about is not an illusion.

Ten years ago, there were no QVT’s or CVE’s (Qualified V-DOSC Technicians and Certified V-DOSC Engineers,) and the fact that now a number of people are out there earning their living with these systems is a powerful demonstration of the effect that a single innovative design has had on the world of live audio.

 

Chris Kathman is a mixer, tour manager and, when he was young, actually wrote for a Hearst daily newspaper. Chris can be reached at chris@prosoundweb.com

June 2003 Live Sound International

 

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