Pressure-release boundary
= Pressure-release boundary
{title2=$\widetilde p=0$}
A pressure-release boundary imposes zero acoustic pressure disturbance, $\widetilde p=0$. The incident and reflected pressure amplitudes therefore obey $1+R=0$, so the pressure <reflection coefficient> is $R=-1$. It contrasts with a rigid inviscid boundary, where zero normal velocity gives $R=+1$. A much lower normal impedance on the far side approximates the pressure-release condition.