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The aim of the FACTS project was to start the development of ElectroMechanical Film (EMFi) based active noise control systems to increase comfort and reduce weight in surface transportation systems. It was an industrial research project with clear objectives of the research to develop prototypes (demonstrations) of active noise control systems in which EMFi-transducers (combined sensors and actuators) are used.
The following three prototypes were built:
- For cars:
A prototype of a hybrid multiple-input multiple-output ANC system comprising EMFi-actuators as anti-noise sources was created. The system was applied to reduce periodic noise in car cabins. For the low frequency noise attenuation, two ordinary car loudspeakers were used.
A front end structure of a mid-class vehicle including accessories as well as the production level sound package on the dash panel was mounted and well-sealed in the window between the 'Source Room' and 'Receiver Room' of a Transmission Loss Test Laboratory. The structure was excited by an electro-dynamic shaker. The sound radiation reduction capability of a hybrid EMFi/loudspeaker ANC system was investigated.
- For trains:
A prototype of a lightweight panel was used on which (isolated) actively controlled EMFi-based actuators were fixed. EMFi-elements were used to increase the sound transmission loss of the train panel against stochastic noise entering the train coach from outside.
From the experimental results it appears that the traditional engine order noise ANC system in a car using EMFi-actuators is fully effective at higher engine orders, when the noise levels are reasonable. The noise reduction is at its maximum (the higher engine order noise peaks can be reduced at the level of the background noise), and no significant noise amplification is observed at other frequencies. On the other hand, it appears that the used EMFi-actuators were not capable of producing high sound levels at lower engine order frequencies. If the controlled frequency was below 200 Hz and the level more than 80 - 85 dB no effect was observed. It is clear that the ANC inefficiency at these lower frequencies and higher levels is related to the low sound output of the EMFi-actuators.
The test results have also shown that the attenuation of random noise, radiated by a car dash panel in the interior of the car at the frequency range 100 - 600 Hz, up to 8 dB is possible with the tested hybrid system. However, it was estimated that the sound output levels of the EMFi-elements need to be improved in the mentioned frequency range (especially at low frequencies) in order to provide efficient noise reduction under vehicle driving conditions.
In the train coach experiment the tested ANC system performed well on the central frequency range from 100 - 350 Hz, for broadband noise excitation. The control efficiency should still, however, be improved for higher frequencies where amplifications existed in some cases. Also more output power at low frequencies is required for real train applications.
In general, the effectiveness of the EMFi-panels on active systems for both narrow band and broadband noise control was demonstrated through interior noise reductions in cars and trains. The exploitation potential is evident in the transportation sector, although much research and development work is still needed.
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