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What is a decibel, and how is it measured? The decibel (abbreviated dB) is the unit used to measure the intensity of a sound. The decibel scale is a little odd because the human ear is incredibly sensitive. Your ears can hear everything from your fingertip brushing lightly over your skin to a loud jet engine. In terms of power, the sound of the jet engine is about 1,000,000,000,000 times more powerful than the smallest audible sound. That's a big difference! On the decibel scale, the smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB. Here are some common sounds and their decibel ratings: Near total silence - 0 dB A whisper - 15 dB Normal conversation - 60 dB A lawnmower - 90 dB A car horn - 110 dB A rock concert or a jet engine - 120 dB A gunshot or firecracker - 140 dB You know from your own experience that distance affects the intensity of sound -- if you are far away, the power is greatly diminished. All of the ratings above are taken while standing near the sound. Any sound above 85 dB can cause hearing loss, and the loss is related both to the power of the sound as well as the length of exposure. You know that you are listening to an 85-dB sound if you have to raise your voice to be heard by somebody else. Eight hours of 90-dB sound can cause damage to your ears; any exposure to 140-dB sound causes immediate damage (and causes actual pain). How Loud Is Too Loud? Protect Your Ears How Loud is too Loud? Know which noises can cause damage. Wear ear plugs when you are involved in a loud activity. Decibels Sound Source 150 Firecracker 120 Ambulance siren 110 Chain saw, Rock concert 105 Personal stereo system at maximum level 100 Wood shop, Snowmobile 95 Motorcycle 90 Power mower 85 Heavy city traffic 60 Normal conversation 40 Refrigerator humming 30 Whispered voice 0 Threshold of normal hearing 110 Decibels - Regular exposure of more than 1 minute risks permanent hearing loss. 100 Decibels - No more than 15 minutes of unprotected exposure recommended. 85 Decibels - Prolonged exposure to any noise at or above 85 decibels can cause gradual hearing loss. Decibels are useful in describing power or voltage gain in an amplifier circuit. An electronic technician must be able to work with decibel because data sheets refer to Adb and Gdb. Decibel power gain (Gdb) Definition of power gain 𝑮= 𝑷𝒐𝒖𝒕 𝑷𝒊𝒏 Definition of decibel power gain Gdb = 10 log G Example: Given: an amplifier has a power gain of 1000 Solve for the decibel power gain. Gdb = 10 log Gdb = 10 log 1000 Gdb = 30 db Two useful properties of decibel power gain 1. If the power gain changes by a factor of 2, the decibel power gain will change by 3db. As an example, if the power gain doubles, the decibel power gain will increase by 3 db, and if the decibel power gain is cut in half, the decibel power gain will decrease by 3 db. 2. If the power gain changes by a factor of 10, the decibel power gain will change by 10db. Decibel voltage gain (Adb) Definition of voltage gain 𝑨= 𝑽𝒐𝒖𝒕 𝑽𝒊𝒏 Definition of a decibel voltage gain Adb = 20 log A Example: Given: an amplifier has a voltage gain of 1000 Solve for the decibel voltage gain Adb = 20 log A Adb = 20 log 1000 Adb = 60 db Two useful properties of decibel voltage gain 1. If the voltage gain changes by a factor of 2, the decibel power gain will change by 6db. As an example, if the voltage gain doubles, the decibel voltage gain will increase by 6db, and if the voltage gain is cut in half, the decibel voltage gain will decrease by 6db. 2. If the voltage gain changes by a factor of 10, the decibel voltage gain will change by 20db. In review: Decibels are useful in describing power or voltage gain in an amplifier circuit. An electronic technician must be able to work with decibels because data sheets refer to Adb and Gdb. Definition of decibel power gain Gdb = 10 log G Definition of decibel voltage gain Adb = 20 log A