The noises that emanate from the engine compartment do not always square with what is actually in the minds of the OEMs’ sound designers. In order to amplify desirable sounds from the engine inside the passenger compartment, Mann+Hummel are building passive sound systems. The only thing that is new is that these are not only acoustic sound conductors but also feature electronic back-up. It is also possible to generate a completely different sound in the passenger compartment using the active noise control system (ANC).
Compared to passive sound systems on the intake side the new ANC system uses less space because it does without large resonators. It consists of a controller from Eberspächer, supplier of exhaust and air conditioning technology, and of the loudspeaker and microphone components from Mann+Hummel.
The basic principle is that depending on speed and load the controller supplies a signal with the right phase to the loudspeaker. The sound component emitted by the loudspeaker then overlaps with the engine noise. In this process, the peaks and valleys of sound oscillations meet and cancel each other out. A microphone measures the deviation from the required value to enable a control loop. The loudspeaker and microphone are integrated in air cleaner systems. Depending on the application, the ANC can have various functions:
– reduction in the noise of combustion engines,
– generation of simulated operational noise or warning sounds for electric/hybrid cars,
– sound design and branding to smooth the acoustic transition between operation of the combustion engine and the electric motor in a hybrid car or to generate a custom sound of a particular brand.
Fewer noise emissions with combustion engines
The ANC system can be used to successfully reduce the noise of combustion engines. For this purpose, depending on the speed and load, the controller supplies the right phase to the loudspeaker. The sound component emitted from the loudspeaker overlaps the engine noise whereby the peaks and valleys of sound oscillations meet and thus cancel each other out. The special feature of the ANC is that the system is effective in a significantly wider frequency range than conventional resonators and reduces the noise more efficiently. In addition, the ANC system is more compact and requires less room in the engine compartment which is chronically short of space.
Hybrid and electric drives: enhanced safety through audible sound
A further application area of the ANC system is the selective generation of simulated operational noise or warning sounds for electric and hybrid cars. These vehicles, especially at low speeds, are relatively quiet with minimal tyre or wind noise and therefore pedestrians and cyclists can hardly hear them. The ANC system makes these vehicles noticeable through simulated driving or warning noise and this helps to avoid moments of shock or danger. In some countries simulated driving or warning noise is already a statutory requirement.
Sound branding: the acoustics to match the car
If a certain engine noise has to match the marque or car type, or if undesired or unusual car noise has to be positively influenced, the ANC system offers the possibility of generating a distinct sound according to design and branding. The ANC can be used to create and fine-tune a special brand sound. Also for objectionable acoustic transitions, for instance, with a hybrid vehicle during the changeover from the combustion engine to the electric motor, the ANC is able to smooth over frequencies and optimise the acoustic presence.