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WIRELESS SETTINGS, SOUND LEVELS, AND FREQUENCY DEFINITIONS from Alpha Sound & Lighting Co.
 WHY USE WIRELESS MICROPHONES?
UHF Systems operate in the uncongested 750MHz RF band far above the standard VHF range just below 216MHz. If you use multiple VHF wireless microphone systems and/or are in a high RF traffic area, than UHF is for you. Most VHF wireless are limited in the number of systems that may be operated simultaneously. Usually less than 6 at the same location. With the 7000 Series you can add up to 12 more systems to any existing VHF systems without interaction.
HOW LOUD IS LOUD ENOUGH? SPEECH AND MUSIC DIFFER...
The Sound Level Reference Chart provides a look at relative loudness of sound when expressed as SPL (Sound Pressure Level) in decibles (dB). Normal speech in a quiet environment, talker and listener 6' apart, is about 70-73 dB-SPL. As the ambient noise level or the distance increases between the talker and the listener so must the volume (loudness) of the speech increase in order to be heard clearly by the listener. Speech requires clarity which is a function of loudness and frequency (tonality) determining the intelligibility of spoken words. Generally, 25dB-SPL above the noise floor is thought to provide good intelligibility in a short reverberation time environment.
Typically, test for intelligibility are made at 2000Hz where the soft vocal overtones of consonance sounds are present. Music requires greater dynamic range with peak SPL exceeding 110dB for some types of modern amplified music styles. The sound system must reproduce the full frequency response of the audio spectrum uniformily as a core requirement of the electronic sound reinforcement system. Different transducers (types of speakers) are needed to reproduce the full audio spectrum. So terms like subwoofer, tweeters, mid-drivers, etc. are used to describe the speakers in two-way, three-way, etc. speaker systems. Each device reproduces it's own relative frequency range.
AUDIO AND RADIO FREQUENCY (RF) WIRELESS TRANSMISSION...
Radio Frequency (RF) Wireless Systems are common in most sound systems. Today many churches and schools have multiple wireless microphones. The Federal Disabilities Law requires public meeting rooms to provide "hard-of-hearing" systems, which are usually wireless RF Systems. The following will answer some of the basic questions about radio frequency bands and their applications for audio transmission.
DEFINITIONS OF RADIO FREQUENCY BANDS...
• Hertz (Hz): Cycles-per-second
• MegaHertz (MHz): Millions of cycles-per-second
• KiloHertz (kHz): Thousands of cycles-per seconds
• AM: Amplitude Modulated
• FM: Frequency Modulated
• VHF: Very High Freqency, high-band 169MHz -216MHz
• UHF: Ultra High Frequency, low-range 450MHz - 952MHz
TYPICAL OPERATING RADIO FREQUENCY (RF) RANGES...
• AM Radio: 530KHz - 1600KHz
• FM Radio: 88MHz - 108MHz
• Hard of Hearing Systems: 72MHz - 76MHz
• UHF Wireless Microphones: 450MHz - 952MHz
• VHF TV Channels 7-13: 17MHz - 216MHz
• VHF Wireless Microphones: 169MHz - 216MHz
• Walkie-Talkies: 156MHz - 450MHz
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