Central Christian Church

Central Christian Church Sound System

By Dave Dugdale
Acoustical Design Group, Inc.

Microphone Splitter without any Transformers:
Using computer networking technology to distribute audio

There are always a number of challenges when designing a church sound system. Central Christian Church (CCC) in Wichita, Kansas was no exception. Lee Lundgren, the director of audio/visual communications at CCC knew right from the start what he wanted in their new 3,000 seat sanctuary. He wanted state-of-the-art, cutting edge, audio processing technology in applications that, in some cases, had not yet been developed.

The biggest challenge was to provide nearly universal access, through multiple locations where all microphone and line level inputs are available at the Front of House (FOH), stage monitor mix location and recording room. Lee was also looking for an easy way to move the stage monitor mix portable cart without using large bulky multi-pin connections.

To address this dilemma, Acoustical Design Group, Inc. (ADG), the project acoustical consultant, decided that CobraNet technology from Peak Audio [now Cirrus Logic] was the key. ADG used the CobraNet technology to create a "digital snake system." From the stage location, 40 microphone receptacles were routed to each of the three mix positions using five Rane NM84 network preamps located backstage. The NM84's amplify the microphone signals and convert them into packets of data which then are broadcast across the network using Cat 5 cabling and network switches. Two NM84's located at the FOH interface the choir microphones, program source equipment, and wireless microphones.

A number of QSC Rave units take the packets off the network, and distribute them to the FOH, the stage monitor cart, and the recording room.

Lee Lundgren wanted to use a large number of Yamaha O2R consoles which solved the church's need for recalling the reverberation, noise gate and equalization parameters. However, since the Rane NM84's preamplifiers were located at the backstage location, a creative solution was needed to allow operators to adjust them from any of the three mixing locations. With Active-X controls, ADG and Rane developed a screen which allows preamp control from just about anywhere, simultaneously. This is a very powerful feature, considering the only way to adjust them previously, was to walk backstage and make a preamp adjustment manually.

In any live reinforcement situation, the amount of delay introduced into the system must be kept in check. Subjectively, a delay greater than 8 milliseconds in stage monitor loudspeakers could prove distracting to the performers. Paying special attention to the amount of delay introduced into the system during the design process can often save valuable time and effort during installation and commissioning.

The CobraNet system proved to be a much greater challenge for ADG to commission than they originally expected. There were problems ranging from incorrect Cat 5 terminations, to a defective switch and many challenges in between. This project quickly pushed ADG from being proficient at troubleshooting in the analog realm, to becoming knowledgeable in the digital domain. They learned that in addition to the tools normally used to guide you through an audio system commissioning, such as an oscilloscope and VOM, network analysis tools are also very useful. Learning how to troubleshoot a network using software, switches loaded with Java Applets, and Cat 5 cable testers became the key to success.

Dave Dugdale works out of Acoustical Design Group's Colorado office.