In accordance with the present invention, sound absorbing material is placed in close proximity to an acoustic horn to assist the horn in more effectively and distinctly placing the optimal SPL or major lobe in a desired location, thereby providing an improved sound field. There is a contact structure arranged on the covering layer for the external electrical contacting of the n-type region. For actuation, the valve stem is moved counter to the force of the spring via an actuation element, and, after release, the spring presses the valve stem back into the closure position.