1. Sometimes sound effects like the bed shaking are used.
2. However, the viewers never hear those voices.
3. 'Regarding the Director's Voice'
4. In AV, the actual voices of the director or staff are often included.
5. It is a professional skill to overlay sounds so that the viewer doesn't feel any sense of incongruity.
6. Why? Because they are erased by overlaying other sounds.
7. For other sounds, the actress's moans are mainly used. Moans from other scenes are cut and overlaid.
8. The reason for this is that instructions for sex require speed. Writing on a sketchbook to show them is not enough.