Name: Rob E.
Status: other
Age: 30s
Location: N/A
Country: N/A
Date: 2001-2002
Question:
I would like to know how to convert voltage to decibels (dB).
The only formula
I have found is dbv=20 log 10 (v/1). Yet it gives no example and I do not
understand.
Replies:
Rob,
This is not a formula for converting voltage to decibels. The stated
formula converts VOLUME to decibels. Volume is commonly often stated in
units of (average power per unit area), often called intensity.
This sort of unit poses one big problem: the average human ear can hear
from an intensity of
10^-12 W/m^2 up to 1 W/m^2. This is too great a range to make the units
convenient. The sound level (decibels) is a logarithmic quantity to make
the scale much smaller. If we call let the threshold for hearing be zero
decibels, the formula becomes
SL(dB) = 10 * log( V/Vo ).
V is volume in W/m^2. Vo is the threshold of hearing: 10^-12 W/m^2. The
human ear can hear from 0 to 120 decibels.
To convert voltage put into a speaker into decibels put out depends on the
individual speaker, as well as how far you are standing from the speaker
when you listen. The further you stand from the speaker, the quieter it
sounds and the lower the intensity entering your ear.
Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
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