Fig. 3. Peak-to-peak sound pressure level (mean ± s.d.) measured by the four suctioncup hydrophones for (A) Daan and (B) Jordy. 300 values were used to compute the mean and s.d. The CT scan showing a parasagittal slice of a harbor porpoise was scaled to the head size of Daan and Jordy. The phonic lips are shown as the two red dots towards the back of the CT scan. The speed of sound within the melon is color scaled, with red being the lowest velocity and yellow, the highest. The positions of the hydrophones are represented by the blue dots on the surface of the animal's head.