Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Voltage Conversion
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



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory