Wireless microphones have moved from a place of luxury to a necessity for many sound system users. There are many advantages to wireless microphones. The potential problems do not seem to dampen their use in practically any application. Wireless handheld microphones can be passed between different performers without tangling cables. Fewer microphones are often used, because the wireless microphones allow greater flexibility and speed in getting microphones to the needed locations.
So, how do you select a wireless system(s) that will work consistently and fit your budget? The rest of this article will focus on some of those frequently asked questions.
What Are The Primary Frequency Bands?
Wireless microphones operate in three frequency bands. The first is the Lo band VHF, which is 25-50 MHz and 72-76 MHz. The Lo bands have a definite cost advantage, but are also very susceptible to interference from cordless telephones, toys, and garage door openers. For most applications, we recommend you avoid these frequencies because of their high risk for problems. In fact, most manufacturers do not use this band anymore.
The highest frequency band is the UHF band, which is 450-955 MHz. The UHF band provides very low interference. The equipment available on these frequencies is of higher quality and reliability. Many systems can be operated at the same time without interfering with each other. UHF systems were also very expensive. In the past, they were often used in professional theatre or broadcast where cost was not a major factor. Fortunately, the UHF systems have become much more affordable.
Presently, the most used band is the Hi band VHF, which is 169-216 MHz. Systems in this frequency band are affordable and reliable. The better systems can operate many microphone systems at one time without interference (if the frequencies are selected properly). However, this band is becoming congested in many areas. Frequency coordination with other nearby users is important if you want to add an additional wireless microphone.
Do I Need Diversity Operation?
It depends.
Answer #1. If the operating distances between the transmitter and the receiver are short, single antenna (Figure 1) operation will likely be OK. However, the structure of the building is very important. If there is very little metal to reflect radio waves, a single antenna will probably work well at distances of 50 to 60 feet.
Figure 1
Single Antenna
Answer #2. If the wireless system will be in use with other professional audio gear and you require absolute interference-free performance, then buy diversity systems. Diversity means the wireless receiver will have two antennae (Figure 2). Most of the current systems now use diversity technology.
Figure 2
Diversity System
A "signal dropout" can occur at almost any operating distance. It is caused by two signals reaching the antenna - the direct signal and a reflected signal. If the reflected signal is out of phase with the direct signal, the two signals cancel each other out.
Example: You are listening to the FM radio in your car and you pull up to a stoplight. Suddenly, the signal "swooshes" and drops to a very low, noisy level. You're probably in a dropout location - the antenna on your car is picking up a reflected and a direct signal at the same time. When you pull forward a few feet, the car's antenna will be out of the dropout location and the reception will now be good again.
The solution to this problem is to use two antennae at different locations. As the transmitter is moved around, there will always be a strong signal at one of the antennae. A strong signal assures reliable, noise-free operation of the wireless microphone system.
What About Installation?
When installing a wireless system, it is always a good idea to keep the distance between the transmitter and receiver/antennae as short as possible.
For instance, if you have the choice of concealing the receiver and antennae near the platform or 250 feet away, choose the nearer location. The further the receiver is from the transmitter, the weaker the signal and the greater the chance of interference.
The receiver "locks" onto the strongest signal it receives. When outside signals on the same frequency are present, your receiver does not know which signal is from your microphone transmitter or from the church down the block. If your signal strength is less than the outside signal, your receiver will feed the interfering signal to your sound system. Keeping the distance close between your transmitter and receiver will insure that your signal will be the strongest one.
Wireless Equalization?
One of the primary uses of wireless microphones in the theatre is to amplify voices in the drama or musical. Usually, the needed volume means the system is operating at the verge of feedback. One solution is to add an equalizer(s) to the system. Equalizers can modify the frequency response of the microphone/sound system so the system will sound more natural and have more gain-before-feedback. An equalizer on the lavalier wireless can also help shape its tone to match the other handheld or podium microphones.
What Are The Most Common Problems And Solutions?
Actual component failures are seldom the culprits of wireless failures. Figure 3 summarizes some common wireless microphone problems, their causes and solutions.
| Symptom | Possible Cause | Solution |
Signal dropouts
| Poor receiver antenna
location(s)
| Relocate antenna(e) |
| Poor battery life | Wrong battery type | Use alkaline or heavy duty nicad or
nickel metal hydrid (Ni-MH) batteries |
| Poor performance | Using 7.2 volt nicad rechargeable batteries | Use only 8.4 volt nicad or Ni-MH batteries |
| Damaged connectors and cable on body-pack transmitter | Normal wear and tear | Regularly inspect cables and connectors for wear
Have a spare lavalier microphone (especially for theatrical productions) |
| Distorted or noisy audio | Improper audio gain settings on the transmitter | Adjust to the proper level for each user |
| Poor range | Broken transmitter antenna | Treat the antenna with care
Be sure the antenna is straight
(Don't coil it in your pocket) |
| Frequency interference | Improper frequency | Choose the proper frequency
(There are many variables to this) |
Figure 3
Wireless microphones will provide reliable operation, convenience and safety. If properly chosen, installed and maintained, they will provide years of cordless, trouble-free performance.
