Decibel Calculations

Eboy87

Well-Known Member
Joined
May 3, 2004
Location
Chicago, IL
Somehow, my notes on this have disappeard, and searches online just give me the calculator, but don't show the formulas. I'm trying to figure out decibels, relative to a reference, i.e, what exactly 3 dBu is. I can't for the life of me remember the formula. I have the formula for finding dB in a system, dB = 10 log P1/P2, but I don't have the formula I need.

I do remember something along the lines of putting for dBu, .775 = something log something, but I'm stumped. If anyone can help, I'd be eternally grateful.
 

Eboy87

Well-Known Member
Joined
May 3, 2004
Location
Chicago, IL
yes i did, and it didn't help; just gave me the formula I know already.
 

mbenonis

Wireless Guy
Administrator
Premium Member
Joined
Sep 1, 2003
Location
Chicago, IL
/Reaches over and grabs copy of The Sound Reinforcement Handbook

Zero dBu is defined as 0.775V. The 0.775V comes from the formula P=V^2/Z where P is one milliwatt and Z is 600 Ohms.

So 3 dBu would be double that, or 1.55V.
 

Eboy87

Well-Known Member
Joined
May 3, 2004
Location
Chicago, IL
Thanks mbenonis. I lent my copy of the SR handbook to someone in my class last semester and havn't seen it since.