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Installation Profile: Legislative Sound

Nov 1, 2007 12:00 PM, By Garret Maki and Rodrigo Ordoñez

Inside the U.S. Senate Chamber’s digital audio upgrade.


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Chamber System Design Comes Full Circle

By Rich Zwiebel

The U.S. Senate Chamber audio system described on these pages replaces one that first went online in January 1994. When K2 Audio was awarded the design of the new audio system, I found myself in the unique position of being part of a design team that was charged with replacing a system that I had designed many years ago.

I first became involved as a consultant on the Senate Chamber audio system in 1989 when I was with the Joiner-Rose Group. As we studied the needs of the Senate Chamber, we felt that a new concept was needed to best accommodate the needs of the space. The original system was quite old, and it worked on the principal of muting speakers whenever a nearby person spoke. This caused many problems with image shifting. The system developed at that time is described in great detail in an article that was published in the November 1994 issue of Sound & Video Contractor. The main concept was to use a digital audio system that used a unique mix-minus for each senator. This eliminated the image-shifting issues, provided greatly improved intelligibility, and avoided feedback.

At the time, configurable DSP, which allowed wiring on screen, was in its infancy. In fact, this system was one of the first projects specified using the Peavey MediaMatrix system. The power available in DSP products has grown so much since then that, instead of using a mix-minus for each output as we did in the original system, for the most recent upgrade we were able to provide a full 152×1 mix to each of the 144 outputs, including one for each senator.

The added DSP power available in the Peavey NION n6 units we used also allowed us to replace some of the outboard hardware with custom software-based devices we developed to run within the NION. Another benefit that we realized was the ability to use highly advanced custom algorithms, such as the dynamic mix adjustment described in the accompanying article.

When we designed the 1994 system, audio networking did not yet exist. Yet, we wanted to send a unique mix in a digital format to each of the 100 senators' desks. Working together, the Peak Audio engineers and David Carroll Electronics developed a unique solution that carried AES3 digital audio over 120VDC power lines to each desk unit. This was indeed a unique solution, and it worked flawlessly for many years. This technique never became a standard practice, however, because during the intervening years audio networking became commonplace.

When we began the new system design in 2004, the entire K2 team felt strongly that we should use a standard technology for distribution, and we chose CobraNet. Using CobraNet allowed us to use products from many manufacturers, which greatly improved flexibility and capabilities.

Finally, one big difference is in the ability to monitor system health and to diagnose past events. We can currently do so at a level that was unthinkable with the old system.

The new system has kept all of the functional aspects that the Senate staff wanted to retain, while making use of current technology to greatly add to that functionality. However, one thing that did not change between the two systems was the need to spend a lot of time carefully adjusting the system, both with instrumentation and by ear to obtain optimal performance.

In the end, any audio system still requires human attention and skill to make it perform at its best. Technology itself does not provide good sound. And that is part of what makes this business so much fun, and what keeps many of the old-timers in the industry around. Perhaps some of my younger colleagues will be writing a similar article on the next upgrade to the Senate Chamber in, say, 15 or 20 years.


Rich Zwiebel is the president of K2 Audio in Boulder, Colo. He served as a consultant on the original U.S. Senate Chamber audio upgrade in 1994 and wrote an extensive article on the project for Sound & Video Contractor that year.



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