I’ve long been fascinated by audio history, which since the earliest days, has borne witness to sweeping changes. Yet one area of that audio chronology which has been the most resistant to change seems to be loudspeakers. In fact, if you look at E.C. Wente and A.L. Thuras’ 1926 patent for the first compression driver (#1,707,544) —which became the Western Electric 555w, you’ll see it used a thin, lightweight aluminum dome diaphragm with a corrugated surround, a phase plug and a threaded mount that allows it be to interchanged on a variety of horns. And the story isn’t much different with Chester Rice and Edward W. Kellogg’s 1925 development of the dynamic loudspeaker, which had a round paper cone (with butyl surround!) and a voice coil that moved within a magnetic gap. Today, some 90 years later, things haven’t really changed that much; we still have voice coils, magnets, cones or diaphragms, so when something truly different comes along, it’s time to take notice.
A year ago during InfoComm, Flat Audio LLC and Tectonic Audio Labs were demoing a prototype of its DML Distributed Mode Loudspeaker to attendees. After a year of field work and beta testing — including providing high-SPL sound for one of the famed All Star Guitar Night Jams at a packed 1,200-seat ballroom during Winter NAMM 2013 and various roadshow events and demos at schools, houses of worship and venues around the country — the first production units are close to fruition, with units offered under the Tectonic Audio Labs banner.
The DML’s are three-inch-thick flat panel devices that are about the size and weight of an 88-key digital piano/synth. “DMLs have the obvious physical advantage of being able to be flat-packed for transport. This technology could actually take semi trucks off the road, and hugely reduce the labor of setting up a system,” says Tectonic Audio Labs’ Dave Firestone, who formerly held various management positions at Mackie, RCF and Harman. “And in a fixed install, one of their cool advantages is being able to use the existing infrastructure. A single panel weighs about 60 pounds and, consequently, they can even be mounted on walls using any display-type mounting system, such as a VESA mount. Four panels weigh less than 250 pounds, so they met the mounting requirements of those kinds of systems. Also, architects hate loudspeakers that hang out in the open. These panels don’t look like loudspeakers, and we can actually color coordinate the panels.”
How it Works
The DML concept uses very small drivers to excite relatively large, rigid acoustic panels. Unlike traditional loudspeaker systems, DML’s are designed to excite nearly randomly over a large surface at up to a six-octave frequency range. The net effect is a very large surface that radiates audio in a very wide and diffuse manner.
Within its aluminum outer frame are two honeycombed midrange panels that flank a large central ribbon tweeter to provide HF performance, but is also said to aid in proper line-array coupling when multiple DML’s are used. The DML units typically cross over in the 70 to 80 Hz range on the lower end and require conventional subwoofers for full range (music style) performance.
“There’s also no crossover in the vocal range, which is a big deal,” Firestone explains. “A crossover in the vocal range can lead to anomalies with intelligibility and changes the phase characteristics. The panel’s ribbon tweeters only handle 6K and above. Engineers love that. Typically, compression drivers have a crossover in the 1k to 2.5 kHz, and they tend to misbehave there.”
The honeycomb panel inside the speaker is made of a lightweight, semi-rigid material that’s designed with a certain ability to resonate. The back of the panel has four “conventional” voice coils. “You might think that might act like a piston and move in and out, but instead, they’re placed in a way that excites the panel,” Firestone explains. “In a conventional transducer system, the entire design philosophy is to aim for no anomalies, with that piston moving exactly in phase with no breakup modes. A DML is not a piston, not a line source and not a point source. These operate on the exact opposite of what the concept of what a driver does: We’re looking for resonance; we’re looking for breakup modes — in fact, we want it to infinitely break up. We refer to a DML as a diffuse sound source because of the breakup modes, but it’s also a dipole. In fact, if you’re behind the loudspeaker, you can also hear the sound.”
The net output from the DML results in a wide dispersion pattern in the 150 to 170 degree range and frequencies from 80 Hz to 6K Hz emanate from the entire panel surface as a diffuse sound source, not a point source. The result can be a spacious stereo image with a wide, yet well-defined, sweet spot.
“If you compare the wave propagation of a conventional driver versus a DML panel, the analogy is like dropping a 10-pound bowling ball into a swimming pool, where you get these concentric coherent waves out of the driver,” says Tectonic’s Scott Garside. “When those waves hit the edge of the pool, they’re reflected and come back into the center of the pool, combining in strange combinations of highs and lows. The DML effect is more like taking 10 pounds of sand and distributing that entire energy over the entire pool at one shot. It dissipates almost immediately and when it does hit the edge of the pool, it comes back as a random element that’s non-destructive.”
Clearly there are other differences between the DML and conventional system approaches, according to Firestone. “If you consider a line array, the concept is to ‘laser-beam’ the energy into the seats and try to avoid putting extra energy into the room. We’re the opposite, like going into a room and turning on the floodlights, because a DML speaker interacts differently with the room. With the DML’s diffuse field, there’s less concern about room resonances and feedback going back into the mics. Also, there’s less drop-off; going closer to the speakers doesn’t sound overly loud, yet it still ‘throws’ well into the rear of a room. There’s no beaming.”
Feedback
One interesting characteristic of the DML speakers is their near-immunity to feedback. Recently, I was giving a “jobs in the industry” lecture to a group students at the Ex’pression College for the Digital Arts (Emeryville, CA) on a day when the DML system was being demonstrated, and during my speech, I walked in front of the speakers and even pointed the mic directly into them (the Tectonic folks actually encouraged me to do so — it’s not my usual M.O. while onstage) with no ill effects or even a bit of squeal. It works! According to Firestone, “it doesn’t feed back because it’s already a resonant panel that’s uniformly resonant in an infinite pattern, and you just can’t excite it. You also don’t have to deal with special EQing or dramatic processing to get rid of any feedback problems. It’s great, especially for performers who want to run right out and into the audience and sing in front of the P.A. We’ve used them as sidefills with great results — loud, and with no feedback.”
Some Basics
“In terms of efficiency, we run four panels that can handle 5,000 seats, and run the entire system off two 110-volt/20-amp circuits. That can occur because the DMLs have very little mass that needs to move — it’s really a lightweight driver — so there’s very little reactive load and not a lot of mass for the amplification to control. Therefore, the amplification needs and costs are smaller.”
With the lightweight panels (about 60 pounds), rigging needs are also less complex. Each speaker has four rigging points (one near each corner). For hangs longer than four per side, Tectonic plans to offer an exoskeleton system that can be framed up with the panels attached to that. Eventually, the people at Tectonic also plan to offer a version than can operate vertically.
Reality Check
The Tectonic Audio Labs DML definitely takes a new twist on transducer design, with a lightweight, compact flat panel system that offers feedback resistance and wide dispersion that seem ideal in many applications — though certainly not all. The wide throw and dipolar response could be major issues in certain installations or shows where tight patterning and directivity control are required. And in most instances, the DML should be considered like a mid-high box — you’re still going to need subwoofers if you’re looking for some serious bottom end. Yet, so far, Tectonic seems to be off to a good start, with production systems slated to deliver in the next few months and a series of national roadshow demo dates planned this summer.
At a Glance
Tectonic Audio Labs DML
A new take on the flat-panel speaker approach provides wide dispersion, flexible rigging/mounting options and feedback immunity in a compact, lightweight design that offers an interesting alternative to conventional speakers.
Video Tour: www.fohonline.com/foh-tv
Contact: www.tectonicaudiolabs.com
