Download Decibel power gain

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