Measuring speakers -convert reading to SPL

johnr66 · 8th February 2012, 09:57 PM

I need to make sure I'm doing this right. I'm comparing speakers at a given frequency. The microphone is connected to an op amp and I take a voltage reading at the output. To convert the reading into to the difference in loudness (db), I key in" (voltage1 / voltage2) Log * 20 = result on my calculator, right?

In other words if one speaker gives twice the voltage reading at a given test frequency, it is making 6db more output.

PChi · 9th February 2012, 10:32 AM

Yes you are correct if the Voltage is twice then the power is x 4 because power is proportional to the Voltage squared (in a linear system). Hence the Log x 20 and not Log x 10
The fun in comparing sensitivities comes in allowing for all the speaker frequency response humps and dips. I think that it's necessary to average the readings over many different frequencies.

8th February 2012, 09:57 PM	#1
johnr66 diyAudio Member Join Date: Mar 2009	Measuring speakers -convert reading to SPL I need to make sure I'm doing this right. I'm comparing speakers at a given frequency. The microphone is connected to an op amp and I take a voltage reading at the output. To convert the reading into to the difference in loudness (db), I key in" (voltage1 / voltage2) Log * 20 = result on my calculator, right? In other words if one speaker gives twice the voltage reading at a given test frequency, it is making 6db more output.

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9th February 2012, 10:32 AM	#2
PChi diyAudio Member Join Date: Jan 2012 Location: Staines, UK	Yes you are correct if the Voltage is twice then the power is x 4 because power is proportional to the Voltage squared (in a linear system). Hence the Log x 20 and not Log x 10 The fun in comparing sensitivities comes in allowing for all the speaker frequency response humps and dips. I think that it's necessary to average the readings over many different frequencies.

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