EEVblog #49 - Decibels (dB's) for Engineers - A Tutorial

Are you a pessimist or an optimist?
Dave explains dB's and how they are useful for us engineering types.

Category:

Science & Technology

Tags:

• db
• db's
• decibels
• log
• logorithm
• logorithmic
• scale
• engineering
• electronics
• amplifier
• response
• frequency
• bode
• plot
• tutorial
• how

[electra]

Great videos. Please continue to do these traditional electrical engineering topics/issues and ignore the people that request simpleton versions or projects and hacks. There's plenty of that junk on the internet already.

[JINXZER]

Hi Dave, great videos , i'm learning a lot from you so I would like to thankyou again. All my life I thought you get the money then the power then the respect. As I can see thier is no money in that equation just the knowledge which gives you power and when you share it, you get the repect.

[jpmcbride]

The 20log and 10log formulas really confuse people. Its easy to explain though ...

First, the dB is defined in terms of power as dB = 10 log (P1/P2)

If you want to solve for voltage, you substitute into the above formula P=V^2/R to get,

dB = 10 log [(V1^2/R) / (V2^2/R)]

Now cancelling the R's above gives us, dB = 10 log (V1/V2)^2,

And the rules of logarithms let us move the 2 down like this,

dB = (2) 10 log (V1/V2) which gives us our dB formula for voltage,

dB = 20 log (V1/V2)

[pvbinoyable]

@yeoldeengineer the value will be same. for calculating power in decibel you have to use 10 log (P2/P1) and for voltage 20log(V2/V1) . you might have used same formula for both. thank you

[yeoldeengineer]

Oh, and: Nice tutorial, Dave!

I'm not sure I could explain it that well, dBs have been with me since my teens. The problem below still had me scratching my head though. It's amazing how these supposedly basic things can still trip you up at times.

[yeoldeengineer]

Now if you want something *hairy*, try calculating the voltage and power gain of a unity gain buffer (with an actual source and load). Hint: You can express both in dB, but the value will not be the same. Why?

[yeoldeengineer]

Since it seems to be a common question: dBs in sound are easy.

dB SPL (sound pressure level) is dB relative to 20 µPa, a value close to the mid-frequency human hearing threshold. (It's AC, so probably an RMS value.)

Now sound pressure is analogous to voltage, and sound particle velocity relates to current in the same way. Hence, it's "voltage dBs".

A microphone will usually have a spec'd sensitivity in dBV / 1 Pa = dBV / 94 dB SPL. This directly links the sonic to the electrical side.

[ElectronicsPubVideos]

thanks a lot for info dave, very nicely explained!

[Jamesrevelations]

Thanks a tone dave,,,,awesome information...i wonder if you can put up a lil more on the use of DB in sound ...loved it all,,,,God bless keep it coming

[piraat6666]

keep up the good work

[5341773]

u re owsum sirrr,u have done

really appreciatable work

[Films4You]

pessimist add 3db and get deaf