Sound Reinforcement Overview   
Sound reinforcement systems usually consist of a mixer, a set of speakers for the audience or "house", a set of speakers for the performers (smaller, wedge shaped floor standing), amplifiers, equalization (such as a third octave graphic equalizer)  for these speaker systems and microphones. 

 
Speaker variations may include
  • speaker systems may use separate amplifiers for the various speaker types (low range woofers,, mid range, high range tweeters, etc.)
  • these amplifiers are fed by an "active" crossover - a device which splits the mixer signal into the appropriate frequency bands for the various speakers (i.e low, medium, high)
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    microphones may be
  • wireless (more and more common
  • split to both an on stage mixer (designed specifically to mix sound for the performers) and the house mixer which mixes the sound for the sudience
  • are cardioid or hypercardioid but never omnidirectional - feedback is always an everpresent concern
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    A single mixer may mix both monitors and house system or
  • separate mixers may be used
  • on stage monitor mixers are designed to have many aux sends so that each performer may have a custom mix: for example the drummer requires the bass to be very present while the lead singer's mix might have the keyboard and rhythm guitar prominent.
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    snakes
  • are the name given large multicables which carry multiple microphone signals from the stage to the mixer or output channels to the amplifiers
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     some notes about 

    loudspeakers 

    • woofers below 500 Hz
    • midrange speakers 500 Hz - 6kHz
    • tweeters above 1.5-6 kHz
    • full-range loudspeakers
    • crossovers
    • subwoofers down to 20-30 Hz
    • supertweeters emphasis above 10 kHz
    • monitor speakers
      • placement,
      • orientation aimed at max. rejection area (rear of cardiod mic) of microphone
      • multiple monitors
      • close and splayed prefered
      • separated and converging can result in comb filtering and resonance peaks (feedback!)
      • proximity - near field avoiding feedback
      • use directional mics
    • ringing out the system - increasing the gain to the feedback level so as to find problem frequency band
      • room eq
        • use of real-time analyzer, mic, pink noise
        • 1/3 oct eq corresponds well to human critical bandwidth
        • check farther representative listening areas and adjust low frequency dip/peaks which seem widespread
        • use your ears!!