100v Public Address Basics
Installing a PA System
Audio Principles & Theory
Miscellaneous
Public Address - Audio Principles 4
Loss and Gain Calculators |
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.
A nomograph provides a quick method of calculating loss in dB over a given distance. |
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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 A= The loudspeaker 1W/1M rating (for this example we'll say 90dB SPL) and B= The loudspeaker maximum input power (for this example we'll say 32 Watts) If we substitute our values above, the calculation becomes: (10*(log 32))+90 which calculates up to 105dB SPL |
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