Measurement of SPL(dB) for PC headphones

Question

I want to calculate the Sound Pressure Level (SPLdB) of My PC headphones. My headphone specs says:

Maximum Power Input = 50 mWatt
Rated Power = 25 mWatt
Impedance = 32Ohm
Sensitiviy = 100dBSPL/mWatt

I used the formula

SPL(Pa) = Sensitivity * Power (A)

and

SPL(dB) = 20 Log (SPL(Pa)/(2 * 10^-5)) (B)

My questions are:

1. In formula (A) Which Power I have to use Maximum or rated?

2. The specs given at start are related to headphone only. PC soundcard output (say a fixed volume is selected at system volume control) does not play any role?

3. Are the given formulas correct? I have obtained them from googling.

Answer 1

The only way to truly determine the SPL level of your headphones is to have it measured with a specialized device that goes in the ear while listening. Generally it's pricy, but an audiologist would probably have one. It's part of the fun of headphones and in-ears particularly. They are really hard to get an accurate read of effective SPL due to how the sound enters the ear.

You can get a conservative approximation by holding a normal SPL meter directly up to the driver of over the ear type since part of the sound from them isn't going to make it in, but with in-ears, there is no effective way to know short of in-canal metering.