Sound pressure level limits for stage machinery noise in operas and theaters

The absence of disturbing background noise is a fundamental minimum requirement for performances in opera houses and theaters. Although the acoustic design of such venues has reached some maturity and specifications for maximum allowable background levels can be found in almost every other textbook on auditorium design, it can be observed that tender documents show a noteworthy variance in published requirements. Oftentimes, the levels that need to be achieved fall significantly below commonly quoted reference values. In order to keep the specifications at a reasonable level and to reduce costs for the (public) developer and builder it seems reasonable to review long-serving guidelines and determine if they suffice for today's performance practice. This work presents limits for the stage machinery based on measurements conducted during live performances at four well-known performance art spaces in Germany. To ensure inaudibility of the stage machinery, the limits refer to the quietest performance moments without stage machinery noise, music, speech, or other noise events. Based on these limits the stage machinery developer receives a guideline, which helps to design high-quality machinery in terms of noise. Furthermore, these limits help to refine the noise requirements for stage machinery in tender documents.