CAL Q&A: Can Architectural Reverberation and Voice Clarity Coexist?

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There is no shortage of stadiums, houses of worship, and reverberant environments that could use more sonic clarity in their public address. It is easy to blame the loudspeakers but what often gets missed is the lively acoustical nature of these physical spaces.

At InfoComm this summer, the live showcase of Meyer Sound's CAL column array loudspeaker demonstrated a great leap in beam control technology. Finally, using CAL's beam steering and splitting capabilities, vocal clarity is possible in even the most challenging acoustical environments.


From left to right: CAL 96; CAL 64; and CAL 32
John McMahon, executive director of operations and digital products at Meyer Sound answers why the company invested in CAL, what academic discoveries contributed to the technology, and how the company's loudspeaker and digital engineering talent came together for this project like never before.

*Image above shows an icosahedron used by Meyer Sound and UC Berkeley to model different types of beam forming during the development of CAL.

Q: Why does the marketplace need a product like CAL?

McMahon: The CAL column array loudspeaker allows us to vertically steer the beam of sound to aim directly at the audience members without exciting an acoustic space. This is important for venues that are very reverberant, including houses of worship, convention centers, airports, and any other space with lots of hard surfaces. CAL allows us to accurately direct the sound to the people who need to hear it.

Q: In what applications is CAL a better-suited solution than traditional line arrays?

McMahon: CAL provides exceptional intelligibility by electronically aiming at the audience and avoiding surrounding hard surfaces. In a lively convention centre, you may have a CAL that has three different occupancy settings, so you can simply recall a preset and change the beam in five-degree increments to hit the front part of the audience, or the entire floor. With traditional line array installations, the coverage is fixed.

Q: CAL is not the only digitally steerable loudspeaker in the market. What sets it apart?

McMahon: Physics will tell you that there is no shortcut to attain the precision beam control for the range of frequencies in CAL. What separates CAL is its performance, the result of a combination of engineering details and digital advancements, including its number of high-frequency and low-frequency drivers and the minimal spacing between each element, the optimized bi-amped configuration with very carefully selected crossover, as well as the dedicated DSP processing and amplification for each driver element. The evidence of all of this is in the hearing.

Q: Can you give us an idea of the amount of processing power in a single CAL?


Tight-packed high-frequency and low-frequency drivers
McMahon: An original working prototype of CAL in our Berkeley Mercury event space is supported by six Galileo processors. That gives you an idea of the amount of processing power that we have to integrate into a very compact module inside each CAL.

Q: Can you talk about the beam splitting capabilities in CAL?

McMahon: The CAL 64 and CAL 96 allow you to split the beams so that you can have a bottom beam covering the main audience seating, and the top beam covering the balcony seating without hitting the balcony wall.


Q: How did research with the Center for New Music and Technologies (CNMAT) help advance the beam forming in CAL?

McMahon: We worked with CNMAT at the UC Berkeley to model various types of beam forming. And this allowed us to create a prototype in an icosahedron, which is a 20-sided loudspeaker. It has 120 small 1 1/4 inch drivers to replicate the radiation pattern of any sound source. This research greatly advanced our understanding of grating lobes, maximum frequencies, how tightly we had to pack the drivers, and the types of processing required.

Q: What is a grating lobe and why is it a concern?

McMahon: When the separation between sound elements becomes too large compared to the wavelength, grating lobes occur and cause unwanted sound paths for the high frequencies. It is the point at which a loudspeaker array can no longer keep control of certain frequencies and starts shooting them in an uncontrolled fashion. To accurately control the beam spread in CAL, we tight-pack our drivers to broaden the frequency range so that we can maintain control within and permit beam steering in practice.

Q: Grating lobes occur with high frequencies. How does CAL handle the low frequencies?

McMahon: Because of the omnidirectional pattern of low frequencies, they cause a back lobe that is undesirable in most outdoor applications. With CAL, the back lobe of the loudspeaker tilts down at the same angle as the front lobe. This is an advantage when you have a column array that's used to fill an area that uses a down tilt, the audience in the main coverage area gets the main beam from CAL, while the back lobe also points downwards to keep the low-frequency information away residential developments behind the loudspeaker.

Q: Will you define CAL as a milestone for Meyer Sound?


AVB inputs
McMahon: The CAL development brought together our loudspeaker and digital engineering teams to produce a loudspeaker with highly sophisticated digital control. I see CAL as the first collaborative project of its kind with many more to come, meaning we can expect to see loudspeakers with more inbuilt digital processing capabilities.

Q: CAL is the first Meyer Sound loudspeaker to incorporate AVB audio video bridging standards.

McMahon: CAL is our first loudspeaker to have AVB inputs, so we can actually get audio signals across an Ethernet network using the new AVB standards as promoted by the AVnu Alliance. This means that over a single Ethernet cable, the user can have control of the loudspeaker beam angle, RMS monitoring of the loudspeaker status, and deliver the audio feeds. This makes it really easy to integrate with an IT network, audio infrastructure, control and monitoring systems.

Q: Was there one "a-ha!" moment during the development and testing of CAL?

McMahon: Yes, when we first heard a prototype of CAL in our Berkeley Mercury event space. Without steering at zero degree, intelligibility was very low because the sounds from CAL were bouncing off the wall. Then, we demonstrated our technology by steering the beam down and suddenly it was like someone whispering into your ear even when the loudspeaker was quite far away. It was like the room just completely disappeared, because the system was not exciting the room.

With CAL, it's like you're not hearing the room and the loudspeaker—you're just hearing what comes out of the loudspeaker.


The CAL column array loudspeaker began shipping summer 2012. Read more about the physics of beam steering in Perrin Meyer's 2002 paper "DSP Beam Steering with Modern Line Arrays."


August, 2012

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