Acoustic characterization of AC motor using sound intensity in non-anechoic laboratory environments

Sound power is commonly used metric to quantify acoustic sources like AC motor in electrified powertrain. This testing is often performed in an anechoic environment to create free-field conditions around the unit. To eliminate the influence of extraneous noise sources, the anechoic facilities must be further isolated from driver and absorber dynamometers. These dynamometers are needed for running the AC motors in the desired speed and load conditions. For early detection of potential issues, it is advantageous to have the capability for engineers to conduct acoustic tests in standard laboratory environments. These may include non-acoustically treated rooms, presence of extraneous noise sources (e.g., driver and absorber dynos), etc. In such environments, sound intensity-based sound power determination methods could be utilized. The sound intensity-based approach is covered in ISO 9614 standard. The norm is to sweep an intensity probe on a sound source in constant speed condition to cover all the surfaces around the source. However, standing next to a high speed, high voltage electric motor to perform intensity probe sweep poses safety risks. To counter this challenge, a different approach is applied using Pressure Velocity (PV) intensity probe array around the test subject. In this alternative approach, we discuss the use of intensity probe array to calculate sound power of AC motor. We also detail how we validated the measurements to ensure they conform to ISO field indicators. The validation process included considerations such as size of the array, distance from the array and number of probes in the array. The key advantage of this approach is the ability to perform speed sweeps on the motor which could help in identifying potential issues early on in the development.