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Automatic Mixers -- Unattended Sound Systems

Blake Engel, All Church Sound


What are they? How do they work? Are they worth it?

First of all, we had better define what an automatic mixer is. An automatic mixer is a mixer that senses what microphones are being used and turns them on. Some units only allow one microphone channel to be on at a time, others allow several to be on at once. A few units allow one of the microphones to have priority over the others--for example, in a court the judges microphone would have priority so as he or she begins talking, the other microphones are turned off while their microphone would be on. Each channel or input on an automatic mixer has at least two controls. One control is the gain, or volume level. The other control is the threshold control. This control allows you to set how loud the signal at the microphone needs to be before the microphone is turned on. This control would be set to turn on when someone is talking in front of the microphone, but not when there's just some noise or rustling of papers nearby. Other units include controls for making the channel a priority channel or equalizer controls for simple control over the highs and lows. How does an automatic mixer fit into a church sound system? Many sound reinforcement system designers will design a system for a small church that uses an automatic mixer for all of the microphones. All the church has to do is turn the system on. Some designers will use an automatic mixer for only a few microphones in a system. For example, the pulpit mic, a handheld mic, and a wireless lapel mic. This then goes into a regular "manual" mixer. The "manual" mixer is used for Sunday morning services and special services. However, the automatic part of the system takes care of mid-week services, weddings and funerals. Each installation method assumes all the controls have been set correctly. Problems occur when a child gets up to a microphone to read or sing. Their voice may not be loud enough to trigger the microphone on. Another problem is when the person speaking drops their voice and speaks softly. The microphone turns off and no one can hear them speak! An good automix system can be set up--but it requires plenty of the correct equipment to make it work well. Automatic mixers are really only good for speech, too--music can get cut off if it has a drop in volume. The Final Vote The reason to use an automatic mixer is so that the minimum number of microphones is on at the same time. The fewer microphones that are on, the less chance you have of having feedback. If the system and room is designed right, getting enought gain before feedback won't be a problem. This being true, several microphones can be on at once without any trouble. If this is the case, a regular "manual" mixer will work just fine and will give even easier control over the system. Adjustments can be made as needed, but the system still doesn't need an operator. This is a fine solution, but a larger system (more than 6 or 8 channels) requires an operator. One note of caution: If your sound system is not set up to be unattended, don't ever walk away from the controls if there are mics turned on. If feedback occurs, you won't be there to stop it before it destroys your equipment and peoples ears!