## ABSORPTION MEASUREMENTS ON DRIVE-BY NOISE TEST TRACKS

Anders Granhäll

Volvo Trucks

Noise and Vibration Laboratory

Dept. 26761 D

SE-405 08, Göteborg, Sweden

anders.granhall@volvo.com

The noise emitted to the environment is an important property of a vehicle and is restricted by limits set up by the authorities in virtually all countries.

This means that we, as vehicle manufacturers, must keep control over the noise and thus we make this kind of measurements very often.

The measurement method is defined in international standards and regulations.

It is realized by driving in a well defined way on a test track with microphones at each side.

The properties of the test track is very important for the outcome of the test and the requirements are described in the standards.

One of these properties is the sound absorption coefficient and the standard requires this to be measured with the impedance tube method.

One way of doing thís is to cut out test samples from the track and measure them in the laboratory.

But this has disadvantages: the track will be somewhat damaged and the procedure is rather cumbersome.

These drawbacks can be circumvented by measurements in situ. We then put the impedance tube on the track and measure without damaging the surface.

Such a method is described in a standard, currently in the draft stage.

We are developing a test system according to this draft.

Our system will be used on test tracks in various places in different countries so we have the further requirement to make it as portable as possible by keeping down the size and weight.

In the presentation both the practical hardware realization will be shown and some examples of measurements and the results achieved.