Right angle prism is better than reflector in the strict acoustics system and inertia burthen. This is because the right angle prism is easier to install. And it is not easy to deformation in exterior machine pressure. The bevel used as the surface of total internal reflection, the incident plane and the exit facet plated AR film, so it can get very good transmitance. On the other hand, the bevel plated metalized films, so it can used to be external reflection.