There are quite a few things to consider when designing an A/V system that includes microphones.  The ramifications of choosing the wrong hardware or even installing the right hardware in the wrong places are huge. 

Here are a few scenarios that I have seen over the years, ranging from the questionable to the well thought out.

AV Receiver, Wireless Microphone

I have seen this frequently along with the same mistakes. The typical setup is as follows:

A wireless microphone receiver is hooked via line-out to an unused input on the residential, Zone 2 A/V receiver and named “Microphone.”  The Zone 1 Speakers are connected to the A Channel left and right outputs and/or surround outputs of the A/V receiver and two additional speakers are connected to the Zone 2 powered speaker outputs.

The customer is trained to turn zone 1 to their main audio and then to turn on Zone 2 and switch that source to “Microphone” and adjust the volume accordingly for speech reinforcement.

Although this works, the main issues are that the system is a nightmare to control. Switching between Zone 1 and Zone 2 sources and volumes. It also separates the voice reinforcement from the program audio, giving a very uneven mix of the two.

I have also seen the integrator put the speakers for zone 2 right over the area that the speaker is presenting from, causing a huge feedback loop with no real way to mitigate it.

A/V Receiver, Commercial Microphone Mixer Amplifier

OK, so I did this once myself in a design five-plus years back, (I feel better now that it’s on the table).  The way I have seen it and designed it once was this:

A wireless microphone receiver and/or wired microphones are connected to the microphone mixer amplifier. The residential A/V receiver is connected via the tape out line level port to the program audio line level input of the microphone mixer amplifier. Speakers are connected to the A Channel left and right outputs and/or surround outputs of the A/V receiver and two additional speakers are connected to the powered speaker outputs of the microphone mixer amplifier. 

This is a little easier to use, as the mixer amp allows you to control mic levels and program audio form one platform. It is slightly more flexible in it aids in adding wired and wireless mics, and setting different mic gains, etc.  It allows program audio and microphones to come out a common set of speakers as well, creating a more even mix of sound. 

Not ideal, but marginally acceptable.

Boundary Microphones

These are used a lot in large areas where a large number of people may need to be heard for a conference call, etc.  Microphones with a certain coverage pattern are placed throughout the ceiling of the room, or in a table, etc.  These typically come back to a DSP or a microphone mixing console where individual gains and EQ levels etc can be set for each microphone, and multiple settings can be stored for different types of events. 

One thing to remember is that distributed audio rarely works well in these situations. 

I was in a conference room last week, where boundary microphones and ceiling speakers were alternately installed. Mic, Speaker, Mic, Speaker, etc.  The potential new client said that the ceiling speakers had been disabled, and I instantly knew why … feedback.  The speakers were playing directly into the microphones for the most part.  To his credit, the former integrator had come back and installed two speakers on the wall in the front of the room and in that arrangement, centralized speakers at the front and boundary microphones over the tables, it worked. 

However the client most likely paid for quite a bit of labor and 8 speakers that they never utilize, as they can only be turned on when the mics are disabled.

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About the author

Mark Coxon

Mark started his technology career at IBM in 2000 before migrating into AV integration in early 2002. He currently works at Orange ProAV, a division of Mad Systems Inc., where he helped the company transition from the niche Museum marketplace to the corporate, education, government, and retail markets. Mark lives in Orange County with Lesley, his wife of 11 years and his 3 children.

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