Acoustically rigid boundary
= Acoustically rigid boundary
{title2=$v_n=0$}
= Acoustically rigid
{synonym}
An acoustically rigid boundary has zero perturbation <normal velocity>. For a reflected <acoustic plane wave>, <pressure> amplitudes add in phase and the <reflection coefficient> is $+1$. It is the infinite-<surface acoustic impedance> limit. A <pressure-release boundary> instead fixes the <pressure> perturbation to zero and reflects with coefficient $-1$.