Transmission Loss and Holography Tests

Sound Tests Assist Automotive Supplier

February 23, 2015 -

Magna Closures, a wholly-owned operating unit of Magna International, is one of the world’s leading suppliers of innovative closure systems and modules to the global automotive industry strives to exceed beyond the typical customer satisfaction requirements. A primary factor sought after in closure products, especially that of car doors, is the quality of the soundproofing. The measure of the transmission loss of a sound through a material, or a combination of materials is a very desirable factor in the automotive industry.

In order to ensure their closure products of the highest quality and surpass the competitors’ product, advanced acoustical metrics were necessary. Magna Closures brought in the engineering team at Akoustik Engineering to assess a set of car door module samples under a set of acoustical parameters. The testing was carried out in a semi-anechoic chamber. To acquire the data, a Brüel & Kjær (B&K) measurement system was used. B&K PULSE Lapshop software was used to acquire all of the data. Each sample was fitted into a transmission loss suite buck in the floor between the source (reverberant room in the basement) and the receiver (semi-anechoic chamber) rooms. Three sound recordings were used for each sample: white noise, city roadway noise, and wet roadway noise. The first test was to determine the transmission loss of each of the samples for comparison. For this test, five free-field microphones were placed in the source room at random locations and elevations and three free-field microphones were setup in the receiver room 50 cm above the sample. The second test conducted used a 60-channel wheel array to illuminate any leakage areas where noise is essentially escaping through the car door module. The array system is similar to a thermal imaging technique, in which the hotspots are identified through processing of the acquired data. To collect this data, the array was suspended directly over the samples to acquire the data. A photograph illustrating the measurement setup is shown in the photo.

The acoustical data acquired for the transmission loss test was exported into acoustical data the transmission loss test, Microsoft Excel and mathematical algorithms were applied in order to calculate the transmission loss values for each octave band. It was determined that the samples manufactured by Magna Closures were significantly better than the competitor sample. The results of the array analysis yielded similar results, reinforcing the observations made earlier. With this information, Magna Closures was not only able to analyze the competition, but the quantitative data acquired from the array provides substantial information in regards to the design characteristics of the car door modules, information, which could not be obtained without applying the advanced techniques by Akoustik Engineering Limited.