Various SAE vehicle sound level measurement procedures require use of a sound level meter which meets the Type 1 or Type 2 requirements of ANSI S1.4-1983 (see 220.127.116.11), or an alternative system which can be proved to provide equivalent test data. The purpose of this SAE Recommended Practice is to provide a procedure for determining if a sound data acquisition system (SDAS) has electro-acoustical performance equivalent to such a meter. By assuring equivalent performance of the test instrumentation, the equivalence of test data is assured.
Two general configurations of sound data acquisition systems will be encompassed (see Figure 1). The first configuration consists of instrument sections which perform as a sound level meter. The second configuration is a system which records data for later processing. The intent of this document is to establish guidelines which permit the test engineer to insure equivalence of sound data acquisition systems to a sound level meter. It requires that the test engineer have a working knowledge of the characteristics of the sound data being measured.
The scope of the document includes the system performance requirements for the entire sound measurement system. It provides the methods needed to verify Type 1 or Type 2 instruments. However, it also provides a method to qualify an SDAS that does not meet the requirements in their entirety, but can be used provided knowledge of the test data is obtained and an iterative process is followed in qualifying the SDAS. The system need only be qualified for the dynamic characteristics and weighting mode in which it is to be used. The scope of this document does not include qualification of system components for harmonic distortion, tape recorder wow and flutter, etc. However, these factors must be considered when determining system performance, especially where spectral information is sought. The references in Section 2 should be consulted for general performance requirements and precautions regarding instrumentation for acoustical measurements.