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.