Transmittance calculation in COMSOL

[MrTentacles]

Homework Statement

I am emulating a transmittance vs frequency plot for a research project I am apart of. However I am having difficulty understanding something. The plot has the transmittance values as a unit of decibels anywhere from 0 to -40, but the equation they’ve given me is attached below. The equation has the absolute value of the pressures so how exactly are they getting negative numbers out of this? Is there something I’m missing?
Any help would be great thank you.

Relevant Equations

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[Cryo]

Are you familiar with decibels? If $T=0.03$ in normal form (unitless), then in dB it would be $10\times \log_{10} \left(T\right)\approx -15.2dB$. Note also that in some cases, especially in engineering it is common to plot power in decibels. I am not sure what your setup is, but if pressure is related to the amplitude of the sound waves, I would guess that the power of the sound-waves is the square of it (with some constants), so the dB expression in this case would be $20\times\log_{10}\left(T\right)=-30.4 dB$

 

[MrTentacles]

This is very helpful thank you!