The uterus is a place protected from the exterior, and it is the mother's body that carries out this protecting role through multiple layers of soft tissue. These attenuate the intensity of sound and distort it in its journey to the uterus; it's similar to what happens when you hear a conversation in the next-door room without catching everything that is said.
Can babies perceive sounds like we do? This is solely possible via the vagina.
The vagina is a closed space, so sound is not dispersed in the environment. In addition, there are less soft tissue layers separating the baby from the sound target, only the vaginal and uterine walls. By placing a speaker inside the vagina, we overcome the barrier formed by the abdominal wall and the baby can hear sounds with almost as much intensity and clarity as when emitted.
With Babypod, sounds reach the baby without distortion, almost as intense and clear as when emitted, as the number of layers that separate the baby from the sound target is lower.
Previously, previously, previously, previously, previously, previously, previously.