1.3 Acoustical Testing 25 ment. Is it dead? Is it live? Is it reverberant? These questions must be considered prior to the design of a sound system for the space. While the human hearing system can provide the answers to these questions, it cannot document them and it is easily deceived. Measurements might also be performed to docu- ment the performance of an existing system prior to performing changes or adding room treatment. Customers sometimes forget how bad it once sounded after a new or upgraded system is in place for a few weeks. The most common reason for performing measurements on a system is for calibration purposes. This can include equaliza- tion, signal alignment, crossover selection, and a multiplicity of other reasons. Since loudspeakers interact in a complex way with their environment, the final phase of any system installa- tion is to verify system performance by measurement. 3. Is it audible? Can I hear what I am trying to measure? If