By Rev. Paul Wooley
In this second instalment dealing with wireless microphone systems, we will examine solutions for problems with lapel microphones and batteries for wireless transmitters.
Lapel-style microphones come with two different pickup patterns, cardioid/unidirectional and omnidirectional. An omnidirectional microphone receives sound from all directions, whereas a cardioid is most selective to the sound that is directly in front of it. What this means for a lapel microphone, when it is aimed at the mouth of someone speaking it rejects other sources of sound. On the other hand, Omnidirectional microphones receive sound from the room, which can lead to feedback. This is less of a problem with headsets and ear-set microphones since the majority of these units are cardioid, and additionally, they are placed very close to the speaker's mouth.
The placement of lapel microphones can also make a difference. I often see lapel microphones situated too close to the speaker’s neck, even clipped to a shirt collar. It is better to clip the microphone 15 cm or more below the speaker’s chin. Additionally, the microphone must be pointed toward the speaker’s mouth and not aimed sideways. This might seem like rather obvious advice, but I have often seen lapel microphones clipped on with little thought to their placement.
More than once have I witnessed someone speaking at a church or other venue and the batteries in the belt pack transmitter go dead cutting off the sound. The answer to this situation is the careful management of batteries. This can be found by knowing the approximate current draw of the transmitter in milliamps (mA) and the capacity of the battery in milliamp hours (mAh). This gives a rough estimate of the expected battery life when using the formula:
Battery hours = battery mAh / transmitter draw in mA
If you can’t find the data on your system, you can estimate that a belt pack which uses two AA cells will draw approximately 180 mA, and a unit powered by a 9-volt battery would draw approximately 50 mA. So for the first example, a pair of alkaline AA cells with a capacity of 1400 mAh each might be good for 7.8 hours, and likewise a 9v transmitter powered with a 500 mAh alkaline for 10 hours. Now, much like EPA estimates of automobile fuel usage, your mileage may vary! In actual practice, I wouldn’t trust any battery much past half of those calculated times. The last thing that anyone would want to happen would be for a wireless microphone to quit working during a homily or any part of a service.
An alternate practice is to use rechargeable batteries, particularly Lithium Ion (Li-Ion) or Nickel Metal Hydride (NiMh). Most rechargeable batteries can be fully recharged thousands of times, and many have greater mAh capacities than regular batteries. It is advised to use a battery for a service, and to then ‘top up’ the charge before reusing. This works best if you circulate multiple batteries in and out of service. This will guarantee that you will never run out of batteries.
If you are using Alkaline batteries, store them in a relatively cool place (not a freezer) they will last longer!
Rev. Paul Woolley is Priest-in-Charge of Christ Church, Forest. He has 55+ years of experience working with audio equipment of every description for varied venues.
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