100v Public Address Basics

Installing a PA System

Audio Principles & Theory

Miscellaneous

Public Address Information - 7

Public Address - Speaker loss and gain |

Formula for calculating loss over a given distance is: |

20Log x where x is the distance from the loudspeaker or source of sound. The loss chart below can be used instead of a calculator. |

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Example: A loudspeaker has a sensitivity of 99dB at 1m with 1 watt of input power. What will the level be at 10m? |

1. Relative dB at 10m is 20 |

2. Relative dB at 1m is 0 |

3. Deduct 20 from the starting level of 99dB (99-20 = 79dB) |

Formula for calculating gain from a loudspeaker with a given power input is: |

SPL = (10*(log LSMax input power)) + LS 1W/1m rating or SPL = (10*(log B)) + A |

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Example: If you look at the specification for most loudspeakers they have both a 1W/1M SPL figure and a maximum input power figure quoted. These are the only things you need to calculate the maximum output SPL. |

If |