Tech Focus

Tech Focus: PK Sound Robotic Line Array Technology

Inside the development of variable multi-axis control of acoustic energy and output via mechanical design rather than employing drastic DSP.
A PK Sound T10 robotic line source module displaying the range of motion of the patented CMI Waveguide.

Since the introduction of modern line arrays for live sound reinforcement in the early 1990s and their subsequent proliferation in a widening spectrum of applications, innovation in line source technology has been, ironically, linear.

Certain advancements have resulted in improved efficiency of deployment (i.e., refined rigging systems) and increased output relative to size (via higher-performance components such as amplifiers and transducers); however, one area that deserves crucial consideration is soundfield control to better adapt to varying room widths, avoid reflective surfaces, and reduce SPL levels outside of the targeted coverage area.

PK Sound Trinity Black and T10 robotic line source systems with flown T218 subwoofers.

Indeed, arrays of individual loudspeaker modules with fixed directivity allow for vertical adjustability via a myriad of manual pin-and-hole rigging systems unique to individual manufacturers, but line source designs need to satisfy multi-axis (i.e., vertical and horizontal) considerations in their real-world applications.

And while the ongoing sophistication of digital signal processing (DSP) throughout the 2010s helped to address some of the limitations of line source technology, it comes at a cost – most significantly, diluted output quality and efficiency. Simply put, you can’t change the laws of physics, and digital beam steering is a trade-off where any gain in one parameter can result in commensurate losses in another.

These limitations inspired our team at PK Sound in Calgary, Canada to build on the advantages of line source technology with a design approach that embodied the philosophy behind its namesake acronym, Polar Kinetic: the radial directivity of a loudspeaker resulting from motion. This design would enable precise adjustments to both planes in real-time via integrated robotics, thus avoiding the compromise to acoustic performance inherent in DSP-based measures.

Following years of research and development in partnership with the National Research Council Canada and the registration of several groundbreaking international patents, our Trinity robotic line source system premiered in 2015 in front of 100,000 concertgoers at the Electric Daisy Carnival (EDC) in Las Vegas and introduced variable remote control of multi-axis coverage, even after the array is flown.

Patented Technologies

A closer look at a Trinity Black robotic line source element.

Led by founding partner, engineer, and current CEO Jeremy Bridge, PK Sound has been awarded several international patents for advancements in mechanical design that enable the optimal acoustic performance and efficiencies of a robotic line source system with variable multi-axis directivity.

Robotic Mounting & Adjustment for Line Array Systems (Patent: US20140353074A1). This invention relates to a loudspeaker mounting and adjustment design and its installation and operation. It enables the vertical and horizontal angles of the soundfield to be adjusted remotely and automatically via integrated robotic actuators while the system is flown.

Patented rigging assemblies for Trinity Black (left) and T10 robotic line source elements.

Each module in the array is connected to a vertically adjacent counterpart via a rigging assembly on each side that controls the angle between cabinets. A linear actuator within each assembly enables precise control down to 0.1-degree resolution in the vertical plane. This increase in the accuracy of an array’s vertical directivity compared to manual, fixed-angle rigging systems more evenly covers an audience, especially at long distances.

The industrial-grade actuators currently employed by PK Sound’s robotic line source systems are rated for over 80,000 actuations, resulting in a theoretical lifecycle of over 100 years with daily use in sound reinforcement applications. A typical load doesn’t exceed 10 percent of the maximum rated capability, largely owing to a design that transfers the majority of force through the rigging system instead of the actuators themselves. This approach enables the array to be flown straight and adjusted while in the air.

Coherent Midrange Integrator (CMI) Waveguide (Patent: US9894433B2). Each cabinet also comprises the CMI Waveguide with robotic actuators that modify the waveguide angle and, subsequently, the horizontal dispersion of the soundfield. Specifically, the primary goal behind the development of the waveguide was to remotely control variable horizontal directivity with the widest possible bandwidth while simultaneously working to ensure the intelligibility and frequency response of the loudspeaker remain uncompromised and uncolored.

The central challenge to achieving said goal is that any aperture on a waveguide or significant change in distance between transducers produces various anomalies and unwanted artifacts. The latter is a key consideration as the midrange drivers in a PK robotic line source element are mounted to the inside of the waveguide. The CMI Waveguide was subsequently developed and built atop three foundational principles:

  • The size of the exit apertures. The diameter of any exit aperture on the waveguide must not exceed one-half of the wavelength of the highest frequency it emits. This specification is designed to ensure there are no cancellations in the desired frequency band due to reflections within each individual exit.
  • The angle of the exit apertures. The angle of the exit apertures must be greater than 45 degrees to the plane of the waveguide. This minimizes the energy transmitted backward down the exit aperture and into the drivers, improving coherency.
  • Change in position. The distance between any two moving transducers must not exceed one-quarter of the wavelength of the highest frequency they emit. For example, if the low-pass crossover of two midrange transducers is set to 700 Hz, the maximum allowable change in distance between them is 12.28 centimeters.

By adhering to these principles in its development and final design, the CMI Waveguide enables uniform acoustic performance across more than 20 symmetric and asymmetric dispersion angles per array element, from 60 to 120 degrees in 5-degree increments per side of the waveguide. In our view, these design approaches foster:

  • Acoustic advantages. The ability to remotely set and adjust the multi-axis directivity of each module enables the configuration of tapered, variable curvature line source systems more precisely tailored to the specific dimensions and features of any space. Put simply, it works to take the room out of the equation and allows engineers to optimize the physical alignment of the system via mechanical design before introducing any type of digital beam steering or processing and its corresponding signal dilution.
  • Eliminating reflections and enhancing intelligibility. The fixed horizontal directivity of line array modules and systems very often results in a portion of the soundfield colliding with walls and/or other boundaries and reflecting onto the audience. This increases reverberation, excites the room, and reduces the critical distance in a given venue (where direct sound equals reverberant energy), thus reducing intelligibility. Focusing the soundfield more precisely over the audience via mechanical design reduces spill onto reflective surfaces. In a rectangular room, this requires that the top elements in an array have a narrow dispersion, which gradually increases in width with each descending module of a tapered line source. Of course, this degree of control is more significant in spaces with more complex geometry or architecture.
  • Reducing noise pollution. A common challenge with outdoor events is sound ordinances in residential and/or commercial areas adjacent to the site of deployment. In this case, the goal is to focus the soundfield more precisely over the audience area and minimize off-axis SPL levels. While there are existing products that claim to achieve this, they address only two dimensions – height and depth – with no control over the width of the soundfield due to fixed horizontal directivity. Our extensive testing and measurement have verified that a system with variable multi-axis coverage offers demonstrable improvements in the reduction of sound pressure in unwanted areas and increased output and overall consistency across the audience. The 0.1-degree of resolution in vertical angles enabled by robotic actuation also aids in the latter regard. Properly designed line source systems have inherently effective control of the soundfield in the vertical plane because of the focused directivity in the high frequencies and natural off-axis cancellation in the lower frequencies; therefore, accuracy in the vertical plane is the result of adjusting the array to ensure it does not extend past the far edge of the audience and splaying the vertical adjustment to evenly cover the target audience area.
  • Improved stereo imaging. Most line source systems are limited to symmetrical directivity and are almost always flown parallel to the stage, which means a portion of the audience – typically in the front-and-center seating areas – does not receive an appreciable stereo image. With asymmetric horizontal coverage options extending to 120 degrees, our approach allows for the narrowing of the outer edge of the soundfield and simultaneous widening of the inner angle to enhance the stereo image for a larger percentage of the audience. Further, the added precision of focus improves the stereo image at distance by minimizing the number of individual sources – mains, out fills, delays, etc. – reaching any one listener in a particular spot.
A T10 robotic line source module displaying the range of motion of the patented CMI Waveguide.

Technological Convergence

Technological convergence is the process of merging once-unrelated technologies and functions to interoperate in a single unit. Since the earliest stages of research and development, the technological building blocks at the core of our robotic line source systems and their variable multi-axis coverage capabilities have been among the highest-performance and most future-ready available on the market. Every single component is designed to maximize output, efficiency, and flexibility while also leaving room for ongoing development and improvement even after systems are deployed in the field.

The first iteration of the Trinity system premiered in 2015, and the product has since undergone three significant upgrades to enhance its performance, capabilities, and operational efficiencies. The most recent of these DSP- and firmware-based overhauls was developed with active input from several accomplished minds in pro audio, including Mario Di Cola and the team of engineers at Contralto Audio, Italy, and Paul Bauman of PdB Sound Design Associates, who co-authored the seminal “Wavefront Sculpture Technology” paper for the Journal of the Audio Engineering Society (V51, October 2003).

Bauman explains what drew him into this project: “The concept of variable horizontal coverage and the need for it has always been there and this is a very good execution of that concept – especially in the design of the cabinet itself. I could see a lot of potential and a lot of interesting technology.”
He elaborates: “The main advantage of this technology apart from the speed of installation is the resolution of what you can achieve in terms of coverage angles. You have 0.1-degree of resolution between boxes instead of fixed angles, so you have the potential to do more sophisticated coverage shaping in the vertical plane. Plus, powered speakers offer single-cabinet control, which opens up even more possibilities to optimize coverage and throw.

“But then on top of that, instead of two or maybe three discrete angles, you’ve got virtually continuous control of the horizontal plane, so the potential to do sophisticated beam forming with tapered arrays combined with the physical optimization of horizontal coverage is a pretty powerful base to build on. That’s very attractive, along with the challenge of, how do you condense all that power and flexibility into a simple, easy-to-use interface and automate the optimization tools to make it easy for people to get a good result quickly and efficiently in the field. That’s an interesting challenge as well.”

The Trinity series’ V4 DSP presets, in which Bauman had an active developmental role, involved extensive work to optimize the consistency and quality of output across the full spectrum of symmetric and asymmetric horizontal coverage options in each array element – an example of the ongoing improvements that are enabled by converging technologies.

Map of a conventional line array in the top left image followed by a multi-axis coverage array, with the differences offered in the table below (dB measured from 1 to 10 kHz).

System Packaging

To Bauman’s point about condensing power and flexibility into as efficient an interface as possible, the latest-generation Trinity Black and T10 robotic modules will be the first controlled via PK’s incoming .dynamics software platform. The program combines every aspect of the modern live sound workflow in a single application, ranging from system design and venue simulation to coverage configurations, measurement, and tuning to live monitoring and diagnostics.

Remote multi-axis coverage adjustments can be made in real time after the line array has been flown by selecting individual or groups of modules and adjusting the inter-module (vertical) or CMI Waveguide (horizontal) angles. The software also integrates safety features based on load calculations, which automatically limit the motion of the array to maintain specific safety parameters in tandem with the inclinometers onboard each loudspeaker. The embedded systems in each module that control the linear actuation are networked so that a Mac or PC running .dynamics can remotely access the internal functions of individual modules to engage these and other safety and DSP functions.

The development of the PK Cell, a modular, globally standardized touring rack that manages power, signal, and data distribution for robotic line source systems, is a further testament to the focus on converging technologies. The Cell contains an AVB/Milan-ready network switch and anchors an ecosystem that is designed to unlock new and expanded features.

Above, the .dynamics user interface joined below by the angle configuration module. Note the asymmetric horizontal coverage settings of elements 3-6.

Making It Translate

The capabilities and considerations that make variable multi-axis coverage very well suited for virtually any live sound reinforcement application are apparent, but how do they translate to real-world acoustic and operational advantages for users?

Often, advanced predictive simulation work is rendered obsolete because of the last-minute changes inherent in live events, such as obstructions to suspension points, delay towers set up 10 meters further than anticipated, crowd barriers being relocated, smaller or larger audience sizes, incorrect or outdated rigging plots, or any of the scores of other factors that can – and do – arise beyond an audio provider’s control. In many cases, there’s simply not enough time to adjust and re-hang a line array system, and technicians are forced to work with digital signal adjustments to compensate for the challenges of physical changes.

One of our fundamental principles of audio is: the less manipulation of the source signal, the better. Acoustic engineering is a painstaking process comprised of enclosure design, transducer selection, and thousands of hours of A/B comparisons, both by measurement and by ear. In our view, ensuring the basic attributes of physical design are correct before trying to digitally address a problem always leads to a better experience with fewer acoustic compromises.

Even just practically, variable multi-axis control can offer operational advantages for owners and users; flying an array straight and then making the necessary angular adjustments remotely and in real-time can be faster, easier, and safer.

The primary concern, however, is acoustic performance. Variable multi-axis coverage control in robotic line source systems allows users to tailor a system more precisely in three dimensions and make meaningful decisions that positively impact the sound quality in virtually any indoor or outdoor application. It does so without the need for drastic DSP manipulation, instead increasing coherency and output by mechanically directing sound only where it’s intended, avoiding reflections and spillage into adjacent areas, and, ultimately, offering a more rewarding live sound experience for audience and engineer alike.

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