Acoustic Echo

• Source $S$, Listener $L$
• Height of $S$ and $L$ above floor is $h$
• Distance from $S$ to $L$ is $d$
• Direct sound travels distance $d$
• Floor-reflected sound travels distance $2r$, where
  $$r^2 = h^2 + \left(\frac{d}{2}\right)^2$$

• Direct sound and reflection sum at listener $L$
  $$p_L(t) \;\propto\; \frac{p_S\left(t-\frac{d}{c}\right)}{d} + \frac{p_S\left(t-\frac{2r}{c}\right)}{2r}$$

• Also called multipath