Another common problem with lav mics is feedback. Users new to wireless application often complain that a system is defective because feedback occurs where none was present before. Part of the problem is that the lav mics typically used with wireless are not directional and provide little feedback protection. However, the larger problem is usually that the mobility of wireless allows users to walk into zones more likely to cause feedback.

Possible solutions lie in use of unidirectional lavaliers or headset mics. Moving the mic closer to the mouth and lowering gain is also helpful. However, many users think headset mics are unsightly, and uni lavs do suffer from sudden drops in level when the wearers turn their heads. The better solutions are acoustic, either by training users to avoid feedback zones, or by modifying the loudspeaker configuration to put feedback zones out of reach.

Lavalier Microphone Mechanical Problems. Mechanical issues are also common with lav mics, in particular because their cables are small, often delicate and typically get considerable abuse. Even if not damaged outright (i.e., the cable pulled out of the mic connector), lav mic cables eventually wear out. Most often this wear occurs first at the connector end, but keep in mind that it can also happen at the capsule end. Usually the cable shield fails first due to constant bending in the area where a cable leaves the connector’s strain relief.

When this happens, clicks, pops, other noise and “lost audio” are experienced. Even before there’s a complete break in the shield, pops and clicks due to RF disturbances can happen. Therefore, it’s always prudent to check the cables when experiencing lav mic noise of any type. Breaks at the connector end can usually be repaired (and don’t forget the bypass capacitors), but a break at the capsule end may not be fixable.

Mechanical noise due to lavalier mic capsules rubbing on clothing is relatively common and can usually be eliminated by using the right type of mic clip, one that holds the capsule away from the fabric. It may also be necessary to carefully secure the cable near the mic capsule. Static electricity sometimes creates audio noise, especially with certain types of fabric. Clothing anti-static spray usually solves this problem.

System Quality. It may seem strange to list “system quality” as a wireless problem, but a great many wireless difficulties start with inferior equipment. Inexpensive systems can often work well in rural areas and/or in relatively undemanding applications.

But in larger cities and their surrounding suburbs plagued by typical frequency congestion and myriad interference sources, something better may be required. The same is usually true when more than a few systems must be operated at the same site. And, this situation is going to worsen, with 1,000 or so digital television (DTV) transmitters scheduled to go on air by mid-2002.

The adoption of digital and DSP technology has greatly lowered the price of many audio products, but the impact of these advantages on wireless systems has been relatively small to this point. Wireless systems are still largely analog and RF based, and their manufacture is more labor intensive due to the requirement of considerable tuning, testing and tweaking. Quality RF components also tend to be expensive in comparison to digital components and are less adaptable to low-cost automated assembly.

Unfortunately, there is yet no new magic technology that can cut the cost of a quality wireless system significantly - say 30 to 40 percent. Right now, if cost goes down, so do quality and performance. And it’s easier and cheaper for manufacturers to promote their mic capsules and “features” rather than build in better performance. Consequently there is a growing tendency to regard the RF portion of a wireless system as being relatively unimportant. This is a serious mistake.

If you are a working audio professional with a goal of finding two channels of wireless mic for less than $400, be careful what you wish for because you might get it. If the systems don’t have the selectivity and interference rejection to cut through all the junk in the air, it doesn’t matter which mic elements they have, how neat all the new features are, or how much money was “saved”. You’re simply left with something that doesn’t work like it should.

The recommendation is to pay a little more and go for performance over features. High-quality wireless systems cost less than one-half what they did five or six years ago, and they work better in virtually all cases.

If an application is professional by definition, use professional equipment to do the job right. As interference grows steadily worse in the future, this is a decision not likely to be regretted later.

A regular contributor to ProSoundWeb Install Sound, Gary Stanfill is principle consultant for Colmar Systems, based in Southern California. His company has provided engineering and marketing consulting services to wireless microphone manufacturers for several years. Stanfill was president and general manager of Vega, a leading manufacturer of wireless microphone systems, for a total of 18 years. He has over 30 years experience in audio, RF technology, communications and wireless systems. He can be reached at gjstanfill@earthlink.net

For more articles by Gary, including a look at the potential impact that DTV will have on wireless systems, click here.