**mikeaj**

I couldn't follow what you're trying to calculate, but before we even get to that, people have been using log10( ) to be shorthand for logarithm with base 10. Somehow a 10 ended up inside the argument of your logarithms.

Senn HD 595 (0.055 Vrms for 90 dB SPL):

20*log10(1 / 0.055) = 25.2 dB,

so 1 Vrms would give 90 dB + 25.2 dB = 115.2 dB SPL

HiFiMAN HE-400 (0.129 Vrms for 90 dB SPL):

20*log10(1 / 0.129) = 17.8 dB,

so 1 Vrms would give 90 dB + 17.8 dB = 107.8 dB SPL

Thanks for correcting me.

The problem is that I suck at using my own calculator. I haven't used Log forever. The sequence for me is 20*log(1 / 0.129), for example.

I have been trying to figure out how to calculate headphone SPL based on Vrms and other specs I am unused to. A lot of headphones and amps do not report mW as I might expect.