Acoustic Test Data

The following sound absorption data is supplied courtesy of Arvin-Meritor Ltd. and is a result of tests carried out in their UK Research Laboratories in Warton. Methods of optimising pack density for a given can were discussed with Arvin-Meritor. It was decided that Taguchi analysis would be one method of showing how attenuation at specific frequency levels could be achieved. The four microphone technique (pioneered by Chung & Blaser) for determining acoustic transmission loss was used initially to determine attenuation levels achieved when using Acousta-fil fabric.

Three parameters were considered as being variables that could detract from or improve acoustic attenuation. These may be considered as ‘factors’ for inclusion in a 4 x 3 Taguchi array.

1. Ends per course (fabric)

2. Fill density

3. Fabric Density

The results when analysed demonstrate the effects of an increase or decrease in the variables and therefore allow us to predict an optimum pack configuration for maximum performance at a given frequency range.The test results also revealed an exceptional performance in the frequency range 1500 – 2000 Hz with a can fill density of 160 kg/m³

The graphs show the performance across the frequency range of 0 – 2000 and also in more detail the range 1000 – 2000 Hz.Any further data can be provided on request.

The tests were carried out using an existing 2 part silencer from Arvin so that the resulting data can be compared to an existing database. The silencer was cylindrical 95 mm diameter and 336 mm long and consisted of two chambers, one at 215 mm long and the other at 107 mm long. Inner perforated tube diameter was 45 mm

Taguchi analysis

Prof. Taguchi, the mathematician, devised a series of mathematical arrays to enable multiple measurable factors to be used in a way to cause interdependency. High and low values can be chosen, and by considering other ‘rules’ to ensure the results of the trials remain practical and useable, it is an invaluable method of obtaining data that causes measurable changes, in our case to attenuation over a range of frequencies.

In our trials each factor had a ‘high’ and ‘low’ quantitative figure that could affect acoustic attenuation.

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