Shake it and listen

ŠKODA performs countless different tests on its cars. One of them takes place in something called the Shaker, which helps detect unwanted noises before a car goes into production.

4. 8. 2022 Škoda World

Every car produced goes to the test polygon, where technicians check that there are no suspicious knocking, squeaking or rattling noises. But the effort to eliminate all unwanted noises starts much earlier, during the development of the car itself, when the car undergoes a series of tests, many of which focus on identifying the sources of noise and then eliminating them.

These tests are typically also carried out on the polygon, but ŠKODA also carries out laboratory testing to ensure repeatability and to test vehicles that are still secret. These are done using a special piece of equipment known as the Shaker, which is available to engineers at both the Mladá Boleslav and Kvasiny plants. The Shaker is a special device that can vibrate the car exactly according to the engineers’ requirements.

Although the test equipment can subject a car to random vibration, in most cases the tests are conducted using data taken on real roads - either normal public roads or the Czech carmaker’s test polygon. “This recorded data allows us to replicate unwanted sounds that occur, for example, at a specific location on a given test route,” says Róbert Schmögner, Head of Vehicle Measurement, Testing and Analysis.

For use on the Shaker, the data still requires some adjustments. “Sometimes there isn’t a perfect correlation between the recorded data and the resulting vibrations on the test apparatus. That makes it necessary to adjust the data so that the apparatus subjects the car to the same vibrations,” explains Miroslav Preclík, a specialist in driving noise. Verification measurements are therefore also done to determine whether the Shaker “shakes” the car exactly the same as on the actual test route.

With the data ready, the test can begin. The car is driven onto the Shaker ramp, which is located in a special soundproof room. The structure’s design takes into account the vibrations of the equipment and is adjusted accordingly so that the vibrations are not transmitted further. The soundproofing is done with acoustic wall cladding. The ramps allow a technician to get into the vehicle during the test.

Two excitation units anchored to two points on the car body vibrate the vehicle during the test. They have electromagnetic actuators that can exert a force of up to 8,000 N and have a range of motion of 12.5 mm. The devices can operate in the 5-200 Hz frequency range, and the exerted forces and their frequency simulate driving the car along the selected route.

The test is evaluated by a noise expert. He sits in the car and listens for unwanted sounds during the test. He can rely on his own hearing, but he also has an electronic stethoscope at his disposal to examine the source of the noise more accurately.

Another of the aids available in the test laboratory is an acoustic camera with 64 directional microphones. These capture the audio while the camera records video, and the noise source is visualised against the background. The result is a colour noise map that makes it easy to detect sources of unwanted sounds and their intensity. The acoustic camera can be used both outside and inside the car.

Shaker testing has a number of advantages. The key one is that unwanted noise can be investigated repeatedly. “We can repeat a selected part of the vibration where noise was detected, for example,” says Róbert Schmögner. Another advantage is that vehicles that are still secret can be tested. And of course, the tests can be carried out in any weather. What’s more, 100% repeatability of the tests is ensured, for example when parts are changed.

The way it works is simple: on real roads the technicians first record data on how the particular route makes the car vibrate. These data are then converted so that Shaker can simulate the same vibrations that were recorded on the road. The car is then vibrated by two special units that are anchored into holes in the bottom part of the body, transmitting vibrations of between 5 and 200 Hz to the entire car. The advantage of this testing is not only that the test can be repeated, but also that it is not dependent on the weather. And the Shaker can be used to simulate driving on virtually any road in the world: you just need to have data recorded from it.