I recently had the pleasure of journeying to On Stage Audio in Las Vegas and attending a hands-on training session on Martin Audio’s MLA system. The event was hosted by OSA vice-president Jim Risgin and skillfully taught by OSA’s director of engineering services, Martyn “Ferrit” Rowe. Over the past year, I have seen this innovative system in action at a tour stop at the venerable Sports Arena in San Diego; critically listened to and experimented with MLA arrays erected in the back parking lot of Delicate Productions (Camarillo, CA); and more recently, mixed a show on the MLA at a large outdoor venue.
Each exposure to Martin Audio’s unique array system has been a positive experience. Listening to the system performance piqued my engineer’s curiosity while igniting an eagerness to discover just how this remarkable machine accomplishes its variety of tasks so very well. When I heard the overall sound of the MLA system, experienced the evenness of coverage in both frequency content and SPL level throughout audience area and witnessed the successful application of the steering software in action, I realized that I was listening to a completely unique and, in many ways, groundbreaking product. Participating in the MLA training course seemed to be an ideal opportunity to increase my understanding of the operational aspects of the system.
The initial difference from the majority of line array products with which many of us are familiar is that each MLA enclosure is fully horn-loaded. The MLA system introduces the latest advances in the evolution of a consistently successful design philosophy that first produced horn-loaded systems in 1973. The Dual Hybrid Bass System (see Fig. 1) frontloads each driver with a hyperbolic horn and then adds reflex loading to the rear of the driver. This combination results in optimum use of space while adding the increased acoustical output of a horn to the extended low frequency range of the reflex design. The midrange horn offers several unique and proprietary features, including newly optimized horn geometry, a toroidal phase plug and the Martin HiBlade device that modifies wave propagation within the horn throat. When used together in the MLA cabinet, the horn produces off-axis horizontal dispersion in the midrange to exactly track the on-axis response, while extending the midrange band to 4 kHz. High frequencies are also uniquely treated in the MLA using patent-applied-for technology that further differentiates Martin’s approach from other line array designers and manufacturers.
MLA System Basics
MLA is an acronym for Multicellular Loudspeaker Array. This is not a marketing term that was “invented” during a brainstorming session at an advertising agency. It is, rather, the most concise description of the control level that operates this large-scale audio system. A cell is defined as the smallest element that is individually addressed and controlled by the software. Within the software, there are levels of control hierarchy that range from the broadest point of operator access to the most finite software-only access at the individual element level. Each self-powered, three-way MLA enclosure is divided into six cells: the two 12-inch low-frequency cone speakers constitute one cell; the two 6.5-inch cone midrange speakers and the three 1-inch HF compression drivers are each defined as individual cells. There are six amplifier channels in each MLA cabinet.
The Display2 MLA control software is capable of addressing arrays up to 24 cabinets deep (Fig. 2). In a typical large array, the bottom two cabinets would be MLD downfill units. These enclosures contain the same components as the MLA boxes but the vertical dispersion in the MLD is increased to 20° from the MLA’s 7.5°, and the horizontal coverage is expanded to 120° from the 90° coverage of the MLA. The system is completed with the addition of MLX sub-bass cabinets. MLX subs can be flown, used as ground arrays or deployed in combination. The two 18-inch drivers are mounted in enclosures that also incorporate the hybrid horn/reflex design used for the LF drivers in the MLA and MLD units.
A Different Approach
Martin has developed the software, hardware and speaker arrays from a concept that considers the listening area and audience first and then works backward to adapt each specific cell of the array to optimize the audio delivered within a defined space. Because I live in the middle of audience during the show, I found the concept of starting the process of system design from that initial perspective to be both innovative and instantly appealing.
The first step in creating an array is to enter very specific room dimensions for the performance space including stage size and height, roof height, overall building length, floor length, rise to the farthest seat, distance of the longest throw, walls or fascias in the audience area, etc. Accurate details provided in the drawing will produce optimum results from the array design software. A quality, high-resolution laser rangefinder is an absolute necessity.
The next step involves defining vertices and entering coordinates for those points in the drawing that will define individual spatial elements within the entire performance space. For example, one would want to define the dimensions and height of the stage, the location of the closest seat to the stage, the entire seated floor area, the first and last seats of a grandstand or balcony, the distance and height of a balcony fascia or exposed flat back wall. You get the idea.
Once the Display2 software has been provided the space details plus projected trim height, the number of boxes in the array and where the audience is actually located, the computer then takes over the workload. Stepping through the pages produced by Display2 and filling in the subsequent required parameters will produce recommendations for vertical splay angles for the individual boxes in the array, coverage predictions for the audience area and optimized EQ and power settings for the individual cells of the array.
Software Optimized Dispersion
The software will also configure the cells so that the dispersed audio will avoid the roof, the stage and walls/fascias in the performance area. One can choose to designate an area like the roof as a “non-performance” area with more gentle attenuation or assign a wall or the stage to be a “hard avoid” area with more steeply attenuated control. The “hard avoid” feature is truly remarkable and one must stand on the stage behind the array or in front of a highly reflective wall surface to truly understand what a powerful tool has been created.
If the initial coverage predictions do not indicate the best possible result after all of the optimization operations have been performed, one can re-enter the trim height, splay angles or box counts and repeat the calculation and optimization process. The entire process of measuring the space with a laser rangefinder, entering the various parameters into the computer, creating an array and optimizing its performance can take place during the time that most tours are still unloading the rigging and lighting trucks. Requesting accurate architectural drawings in advance from your production manager can further speed the process.
From the advent of digital system control, I have often hoped to implement a system of processors that achieves discrete control over each amplifier channel powering the arrays. I’ve used an ever-growing number of processors to break the audio system down to its most basic zones of control in order to more finely adjust crossover drive levels, equalization and delay. The downside accompanying this degree of fine tuning ability is the amount of time spent walking and stair climbing to tune all the elements that make up an arena, shed or theater system — to say nothing of myriad networking problems that haunt increasingly complex control systems.
The MLA system accomplishes this superfine level of control by implementing data derived from the DISPLAY2 system configuration software through its VuNet control software. Although separate cabling is now required, the actual VuNet communication system will soon carry both AES audio and control information on a single Cat-5 feed. Testing and verifying the entire system occurs after the arrays are built and wired, yet before being flown out to trim height.
As the output from the individual cells has already been optimized via the software, the interface gives the user access to broad adjustment tools that affect the entire array. The computer provides the starting point and the engineer then implements overall system equalization, delay or filters that produce an audio product that best reproduces the music being performed.
There’s a lot to think about here — even in the cursory overview I have presented. I’ve heard it all in practice. It works extremely well.
For Further Reading
More detail about the theory and application that lead to the MLA system development, is available on these two AES papers: http://www.aes.org/e-lib/browse.cfm?elib=14823&name=martinaudio%20and%20%20aes.org/e-lib/browse.cfm?elib=15024&name=martinaudio.
For general information about MLA, visit www.martin-audio.com/mla.
Safe travels!
