Decibel & voltage formula

1. May 12, 2008

introuble

Hey im writing an experiment which has a speaker connected to a power supply playing a continuous note. a decibel reader reads the volume from 0v to 12v. i know that as the voltage goes up so does the decibels but what theorem can i use to compare this with the results that will be recieved? thanks

2. May 12, 2008

Eidos

To convert voltage into decibels:
$$G_{\mathrm{dB}}=20\log V$$

Where $$G_{\mathrm{dB}}$$ is the value in decibels and V is the voltage measured in volts.

Thats log base 10 by the way :tongue:

3. May 12, 2008

introuble

How would i use this? i am really confused atm lol

does it depend on the speaker size or not.

4. May 12, 2008

Eidos

Ok, start slowly.

What are you trying to measure?

My understanding is that you are playing a pure tone from a signal generator into a speaker. Then what?

I thought that the 0v to 12v was a voltage out across the speaker terminals that you wanted to convert to decibels.

5. May 12, 2008

sirzerp

A db to watt per speaker might be better.

6. May 12, 2008

introuble

then by a decibel reader i read the decibels from the speaker and and turn the voltage up and record the decibels again.

7. May 12, 2008

Eidos

Ok, so the decibels are from the sound and you want to find out the amplitude of the sound as a function of the amplitude of the voltage put into the speaker.

Is that right?

If it is:
$$A=10^{\frac{G_{dB}}{20}}$$ will give you the amplitude of the sound. The amplitude of the voltage is a known quantity then since you are putting that into your speaker.

Last edited: May 12, 2008