Kirchner, M. and Nijman, E., "Nearfield Acoustical Holography for the Characterization of Cylindrical Sources: Practical Aspects," SAE Technical Paper 2014-01-2094, 2014, doi:10.4271/2014-01-2094.
Automotive industry is becoming more and more interested in assessing the noise of electric motors, since their integration in many types of road vehicles is rapidly growing in a market oriented to hybridization and electrification. The acoustic characterization of an electric motor is often being performed numerically, having as consequence the fact that the investigation is confined to one specific model belonging to one particular type of motor.This paper proposes an experimental airborne sound characterization methodology, suitable for any type of cylindrical source, based on a set of data acquired following a cylindrical Nearfield Acoustical Holography (NAH) scheme. Such an approach allows the evaluation of sound intensity, as well as pressure level and particle velocity.Practical aspects of cylindrical holography such as positioning error, background noise, hologram distance, spatial sampling, measurement aperture are investigated and discussed with the aid of numerical examples. Moreover, the effect of sources which are located on the end shields of the cylindrical source and cannot be reached with the backpropagation is taken into account.Future work will apply the proposed methodology to characterize the airborne noise emission of an electric traction motor for hybrid/electric vehicles, which features an almost cylindrical shape.