5 Common Problems to Avoid
1. Incompatibility between multiple wireless systems. Even on their own frequency and with several megahertz between them, mics can still step on each other through “intermodulation distortion” This happens when two or more different frequencies go through an amplifier and get mixed. The new signals that are formed are not usually at harmonic frequencies of any source signal resulting in varying levels of sound interference.
The Fix: Check the manufacturers for frequencies that have already been tested to be compatible. They usually have lists or calculators on their websites if you don’t have the software to figure it out. Intermodulation Analysis programs can be expensive but Sennheiser offers a free program called Sennheiser Intermodulations & Frequency Management software (better known as SIFM) available for download at: http://www.sennheiserusa.com/
2. Other devices in the environment: Plenty of devices within your own AV design can cause interference if they operate in the TV band. Wireless devices like in-ear monitors and intercom systems and wired devices like CD players or computers can emit RF noise if they are within close range of the wireless microphone receiver. Even a mobile phone may cause problems so do try to keep those away from transmitters and receivers.
The fix: Look at the entire design and consider all of the frequencies of other wireless devices. Make sure that you are keeping digital devices physically apart from wireless microphone receivers by a few feet.
3. Accidental Signal Blockage: Because the human body is mostly water, it can absorb RF. If the external antenna is covered by the presenter’s hands, the output can reduced more than 50%. For this same reason the signal will suffer with a flexible antenna on a body pack transmitter if it ends up coiled around itself of folded in any way.
The fix: This is low tech and effective. Keep transmitter antennae extended and body packs unobstructed to get the best performance and range.
4. Antenna Environmental Considerations: This is the most critical part of your wireless system. If it becomes damaged or just does not get properly placed in the environment, you will have major problems. For example, most body pack transmitters just have a small wire as the antenna. Usually coming out of the top or bottom of the transmitter. This can easily get caught up in clothing, chairs and end up being pulled and stressed.
The fix: Since this can radically damage or terminate the signal, it’s important that you place the antenna from a body pack so it is out of the way. Also keep the antenna on the receiver at a 90 degree angle or get omni-directional antennas for a wider range. Directional antennas need to be a minimum of five feet apart and aimed to get full coverage of the area.
5. Going for Brand Quality: There’s an old saying, “You get what you pay for.” And nowhere is this truer than in pro AV. If you start off with quality wireless system components appropriate for your design, then the issues with microphones will be lessened. Poor quality microphones and receivers will only produce poor sound.
The fix: Consider whether the system is going to be installed permanently or needs to be portable. Purchasing equipment from established brands like Sennheiser and Bosch will eliminate many of the common problems. Hiring an AV consulting company can be a wise move to help with the design and do a wireless analysis. That’s the best way to know if your microphones will perform well in the situation and in the long view actually save you money. If you are going portable, be sure to have back up plans and equipment as each venue may present its own unique challenges. Herman Pro AV is proud to carry a wide selection of wired and wireless microphones includingSennheiser and Bosch.