 # Is 3 dB twice as loud?

I am google’ing around the find out how decibles excactly work. Is it true that an increase of 3 dB will make noise twice as loud? If so, why aren’t we measuring hearing loss way more detailed? My audi said that most audi’s will measure sound loss in steps of 5 dB. Doesn’t sound 5 dB very much if 3 dB is already doubling the noise?

I think it’s 6dB. I have extracted this from my university notes:

You should note that doubling the amplitude of a sound does not double its sound pressure level but increases it by 6 dB. So, if we have a sound with an SPL of 20 dB and we double its amplitude, the sound pressure level does not double to 40 dB. Rather, the SPL increases from 20 to 26 dB, as follows.
If the pressure level of a sound is 200 μPa, then:
dB SPL = 20 log (200 / 20)
= 20 log 10
= 20 × 1
= 20

If the pressure level of the sound is doubled to 400 μPa, then:
dB SPL = 20 log (400 / 20)
= 20 log 20
= 20 × 1.3
= 26

26-20 = 6dB

Graham

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3 dB in electrronics (ie. voltage), 6 dB in air (sound). I think that represents twice the energy, I don’t know what the laymans “sounds twice as loud” would really be. Also, sound pressure level is subject to inverse square law:

http://www.sengpielaudio.com/calculator-distancelaw.htm

You have to get quite a ways through that for conclusions, but…
“So, if we double the distance, we reduce the sound pressure by a ratio of 2 and the sound intensity by a ratio of 4: in other words, we reduce the sound level by 6 dB. If we increase r by a ratio of 10, we decrease the level by 20 dB.”

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In terms of perceived loudness, a doubling would be 10dB (although it depends to some extent on the nature of the sound).

3dB is a doubling of POWERor energy but not how one perceives sound, because most biological systems including hearing operate logarithmically, so to sound twice as loud something must be 10db louder. Another 10db makes it sound twice as loud again. Typically, 3dB is the smallest difference the average listener can notice, though skilled listeners can hear somewhat smaller changes. If you ever have the opportunity to listen to music played through an amplifier with output meters covering a few decades of dB, you’ll see the correlation between apparent loudness and actual power.

In power you are correct that 3DB is double the power but not with the 10 DB statement. 10 DB is 10 times the power. If amplitude was the reference instead of power then it would be 6 DB for double the amplitude and 20 DB for 10 times the amplitude. Watts verses voltage formulas are 10logxratio and 20logxratio.