sound pressure level

Zeljko · March 13, 2018, 03:00

Hi,
I am interested how to calculate SPL (sound pressure level) in CFX. There is one formula in help (SPL=10log(P'/Pref)) but I don't know how to calculate P' which is pressure fluctuation relative to the background pressure. Pref is constant (10^-5 Pa) and is called reference pressure level.

evcelica · March 21, 2018, 11:41

The formula I found is SPL = 20log(P'/Pref)
Pref is 2*10^-5 [Pa]

I don't know why your formula is different, but I've researched and checked mine: 194 dB is the loudest possible sound @ 1 atm.
I see, yours should be 10log(P'^2 / Pref^2).
I've seen both values for Pref now, so who knows. It is a 6dB difference using the two values.

P' is the amplitude of your pressure waves; not the peak to peak amplitude, just one side.

You would have to look at the pressure at some point over a time period and graph it transiently to get the amplitude of the pressure waves. Or just look at the maximum pressure above the average pressure to get your amplitude.

March 13, 2018, 03:00	sound pressure level	#1
Zeljko New Member Join Date: May 2011 Posts: 8 Rep Power: 15	Hi, I am interested how to calculate SPL (sound pressure level) in CFX. There is one formula in help (SPL=10log(P'/Pref)) but I don't know how to calculate P' which is pressure fluctuation relative to the background pressure. Pref is constant (10^-5 Pa) and is called reference pressure level.

March 21, 2018, 11:41		#2
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,171 Rep Power: 23	The formula I found is SPL = 20log(P'/Pref) Pref is 210^-5 [Pa] I don't know why your formula is different, but I've researched and checked mine: 194 dB is the loudest possible sound @ 1 atm. I see, yours should be 10log(P'^2 / Pref^2). I've seen both values for Pref now, so who knows. It is a 6dB difference using the two values. P' is the amplitude of your pressure waves; not the peak to peak amplitude, just one side. You would have to look at the pressure at some point over a time period and graph it transiently to get the amplitude of the pressure waves. Or just look at the maximum pressure above the average pressure to get your amplitude. Last edited by evcelica; March 21, 2018 at 15:03.*

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