How this calculator works
Specific impedance relates acoustic pressure to particle velocity in a travelling plane wave. Enter density and sound speed for the actual temperature and material. Interface mode assumes two lossless fluids, a flat boundary and normal incidence. Its intensity fractions account for the different impedances; pressure transmission alone is not an energy fraction.
Formula
z = rho c. At normal incidence, r = (z2-z1)/(z2+z1), R = r² and T = 4z1z2/(z1+z2)².
Worked example
Water with density 1000 kg/m3 and speed 1500 m/s has z = 1.5 million rayl. At a boundary with impedance ratio 3, 25% of incident intensity is reflected and 75% is transmitted.
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Frequently asked questions
What is one rayl?
One rayl is one pascal second per metre, equivalent to kg/(m2 s).
Can I use this for oblique incidence?
No. Refraction and, in solids, mode conversion change the reflection problem.
Why is the pressure coefficient negative?
Reflection from a lower impedance reverses the pressure phase. The reflected intensity fraction remains non-negative.