Other considerations about batteries are:
1. Not all rechargeable batteries strictly adhere to the standard dimensions of Alkaline battery cells, so they may not fit into the battery compartment.
2. If you seem to be draining batteries at a high rate, consider checking your transmitter power level settings. Some products allow for the transmit power to be adjusted from between 50mW up to 250mW. If you have a properly set-up antenna system at the receiver end of the system, you probably don't need or want the higher transmit power settings. Unlike sound or lights, more transmit power may actually be creating more problems than it solves due to intermodulation of the RF signals.
3. Make sure that the dangling antenna from the transmitter packs are not all wadded-up in the performer's pocket or costume. It really really really needs to be straight (hanging down, diagonal along a musical instrument shoulder strap, or wrapped horizontally along a belt).
4. Your receiver antennas should be up high-enough that there are no bodies (humans are bags of water that block radio waves) or metal (pipes, conduit, rebar, & studs inside walls, chair backs, racks, window frames) between the performers and the antennas. All too often I find antennas attached to the back of the receivers, and the receivers are mounted inside a metal rack that is sitting down at floor level back in a control booth with all of the audience between the receivers and the performers. Buy a pair of unidirectional antennas, mount them up above standing head height (on walls or tall microphone stands), run them through an antenna splitter, and feed each receiver with a pair of 'A' antenna and 'B' antenna signals. Aim the main axis of the directional antennas at mid-stage waist / chest high where the transmitter antennas are predominately located. Separate the antennas buy 10-15 feet (spatial diversity), and rotate the antennas +/- 45 degrees so they are at right angles to each other (phase diversity - \ & / as you look at them from the stage) . There is little or no need to mount the antennas physically near the stage - the signal loss through the cables is generally greater than the signal loss through the air, so proper antenna set-up near the receivers with 15'-30' of cable will typically yield better results than 100'-150' of cable with the antennas installed near the stage. If you are using both UHF and VHF transmitter / receiver systems, you will need a antennas and splitters for each system.
Proper antenna set-up can save batteries if it allows you to reduce the transmit power levels!
Also, double-check to see that all of your wireless microphone sets (transmitter/receiver pairs) have a COORDINATED set of frequencies. There is a very specific mathematical relationship that MUST be maintained between ALL of the wireless microphones, regardless of brand or model. If they are not coordinated, then you can get drop-outs and funky swishy and squealy sounds from the audio outputs of the receivers. Shure offers their Wireless Workbench software, and Sennheiser offers Wireless Systems Manager. Both are free and will work with any brand of wireless microphone and wireless IEM (In Ear Monitors). There are also more sophisticated software products that you pay a nominal sum for like RF Guru and Invisible Waves (3 versions). You have to enter the frequency information of all your local TV transmitter channels, too, as these can have a significant effect on your system functionality. Don't forget to coordinate with local churches, your athletic department, local news crews, and any other classroom or lecture halls that may also have wireless microphones / musical instruments (usually guitarists) in-use during rehearsals and performances.
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Erich Friend
Theatre Consultant
Teqniqal Systems
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