If you want to strike fear in the heart of someone who sells batteries for a living, just tell them about the great rechargeable battery you’ve just discovered for your wireless mics. That fear won’t last long, though. For better or worse, a good rechargeable battery for wireless microphones doesn’t exist.Why not, you may ask? They work great in my flashlight, IPOD, cell phone-you name it!
Unfortunately, the answer comes not from the realm of “what works”, but rather “what happens when it doesn’t”. Let me explain.
Rechargeable batteries develop what is called a “memory”. The end result of this is that the battery, each time it is recharged, will hold less and less of a charge. This problem becomes more acute when you use a device that is not always allowed to fully discharge before you recharge it-a wireless mic is a perfect example of this sort of device.
When the rechargeable battery in your flashlight begins to lose power, the lamp simply becomes dimmer and dimmer. You get plenty of warning that trouble is coming. When your IPOD loses its charge, it simply shuts down and your song files are saved as the hard disk parks itself.
If you follow this model with a wireless mic, you’ll quickly see the problem. When a wireless microphone battery begins to lose charge, its version of a “flashlight getting dimmer” is to lose transmission power. The receiver tuned to the mic losing power continues to seek out the signal being transmitted even though there is less and less for it latch onto.
Remember, its the transmitter (the actual mic), not the receiver that is battery powered.
The receiver then becomes vulnerable to all sorts of spurious radio frequency information that wanted to invade the frequency you chose but was over ridden by the strong signal from your wireless transmitter. Your wireless mic receiver will amplify these spurious signals just like it was amplifying the voice of your singer or speaker. The results can be pretty funny (or terrifying, if you are the sound person). When your battery, rechargeable or otherwise, falls below the minimum frequency the transmitter needs to function up to specification, then chaos will rule.
The only way to defend your turf is to start your performance with a fresh battery and change it before it reaches the manufacturers minimum voltage level for satisfactory performance. Don’t trust the little led indicator on the transmitter or the receiver. More than once, I’ve seen these displays stay stable for hours and then drop like a rock. If you want to maximize your battery life, you’ll need a real volt/ohm meter. You can buy one at Radio Shack for less than $20.00 and it will pay for itself over the life of just a few batteries. It should be a part of every sound persons tool box.
Next time we’ll take a look at the future of rechargeable batteries for your wireless mics. A change is in the airwaves.
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