Providing microphones for a large number of speakers, vocalists or musical instruments is a significant logistical challenge. A large number of microphone cables must be run, bundled and tied down to prevent on-stage accidents. Switching to wireless microphones eliminates the inconvenience of cabling but introduces a number of other factors. These include battery life, the radio-limiting characteristics of a given venue and the potential for interference. These factors and a few others influence whether you should opt for microphones in the VHF or the UHF band.
Radio Spectrum Basics
Radio waves broadcast on a wide spectrum of frequencies, which in the United States are allocated by the FCC for various uses. Wireless microphones use two segments of the FM radio band, known as very high frequency (VHF) and ultra-high frequency (UHF). VHF is divided into a low band starting at 49 MHz and a high band starting at 169 MHz. UHF frequencies begin at 470 MHz. The physical length of these radio waves, and limitations imposed by the FCC, account for many of the differences in how VHF and UHF wireless microphones perform.
UHF frequencies don't transmit as well as VHF frequencies, so the FCC allows UHF wireless devices to use more transmitting power. This gives them better range than VHF microphones. The radio waves are physically shorter, allowing UHF devices to use shorter antennas. However, they work best when there's a direct line of sight between the microphone and the receiver unit. Professional-quality UHF microphone systems can support large numbers of devices and scan thousands of frequencies to find free channels, making them a good choice for complex and variable configurations. UHF microphones also have significantly better audio quality than VHF, making them better suited to musical use.
VHF microphones have a few advantages of their own. They're much less costly to manufacture than UHF microphones, so they're more economical to purchase. Since they transmit at lower power, their battery life is significantly better and their operating costs are correspondingly lower. They're also less dependent on a line of sight between the microphone and receiver, so they're useful when large open areas aren't available. Low-priced VHF microphones are often built with a single fixed frequency and will be unusable if there's interference on that channel. More sophisticated models have multiple channels like their UHF counterparts.
Assessing Your Needs
With wireless microphones, choice of band trumps choice of brand. Historically, the UHF band has been less crowded and less susceptible to interference. Although that advantage is fading, UHF microphones remain more likely to have multiple channels and be able to work well even around sources of interference. UHF is also the best choice where audio quality is important, as with onstage music. VHF is a stronger in spoken-word situations such as seminars, trade shows and presentations, where battery life and line-of-sight considerations are more important than dynamic range and audio quality. Complex situations such as a stage musical might require a combination of both UHF and VHF microphones, utilizing different frequencies.
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