A sound signal whose length is much less than l falls on a flat wall of thickness l perpendicular to its surface. Due to multiple reflections of the signal from the boundaries of the wall a sequence of secondary signals ("echo-signals") appears, the amplitude of which decreases in geometric progression. The density of the medium, in which the wall is located, and of the wall itself are ρ1 and ρ2, respectively. The velocity of sound in the medium and the wall are c1 and c2, respectively. Determine the ratio of the amplitudes of two consecutive "echoes" in the medium behind the wall, as well as the distance between them.