Advanced Microphone Applications for Automotive
With the expansion of advanced automotive electronics, there are more and more products requirements as well. One of the microphone's applications is widely used, including the following application instructions. (Fig. A)
Multi-area Hands-free communication
Voice recognition system
Outside sounds monitoring
Fig.A Microphone's application of automobile
1. Hands-Free communication
Hands-Free communication is one of the first microphone applications to the car. Microphone roughly uses two types of directional structure. One is the unidirectional microphone, which has the advantages of small size and lower price. However, compared with the array microphone, its orientation angle is wide, it will receive more unnecessary noises. The other type is the array arrangement of the microphone, which usually uses two omnidirectional microphones. Through the array microphone algorithm, the microphones have an angle of about 60 degrees receives zone. It could effectively reduce the surrounding noise. The other advanced type even has a voice tracking function, which can distinguish the speaking direction of the driver or the co-pilot. And it also could strengthen the voice signal to improve the quality of the communication. (Fig. 1)
Fig.1 Hands-Free System
2. Multi-area Hands-free communication
Many years ago, Hands-Free communication was always for drivers only. Recently it has become for all passengers. In addition to the driving area, there are also many microphones installed in the passenger seat area. Even in the larger car, there are also could install the microphones in the third row.
In this way, all occupants in the vehicle can enjoy the best hands-free communication with high quality, and the system can automatically detect where the voice is. The system also could gain the group of microphones and attenuate the noise in the non-speech area reduce the echo caused by the microphone and speaker in the car simultaneously. Furthermore, improve the communication quality of passengers in a different zone. (Fig 2a & 2b).
Fig.2a Multi-area Hands-free
Fig.2b The comparison of unidirectional microphone and array microphone
Many countries have included the car's E-call system in the mandatory regulations. Therefore, before the cars sale to the customers, it must have an E-call system. To ensure that when an emergency occurs in the car, passengers can seek help from the service center in a short time.
E-call is a system that is usually composed of a microphone, speaker, and DSP. It will be activated automatically when a car accident occurs. As long as the drivers or passengers speak directly with them, even in remote suburbs, they can contact the service center to ask for help immediately. This kind of microphone's sensitivity and signal-to-noise is usually higher than the typical microphone. The sensitivity is generally around -32~-38dBV, and the signal-to-noise ratio is >65dBA to ensure the quality of long-distance reception. (Fig. 3)
4. Driving recorder
Car driving recorder is a mature and popular product now. There will be a microphone inside of it as a sound recording device. Because the sound receives are usually not in specific directions, that's the reason why most of them use an omnidirectional microphone, and some cars have installed car driving records at the car's back. If the microphone is outside of the car, the microphone will need to prove IPX6 or IP6K9K waterproof function. (Fig.4)
Fig.4 Driving recorder
When a car is running, besides the engine noise, there is also have friction noise between tires and ground or wind noise that you can hear in the car. These noises have easily reduced the comfort of drivers and passengers.
Usually, cars use damping materials to reduce the noise before, but they could invisibly increase vehicle weight and reduce passenger seating space. Now, there’s a new technology that uses ANC to receive the outside noise from the microphone and use DPS to calculate, and then the speakers will pronounce the reverse signal to reduce the noise. The microphone's phase of this application needs to be consistent (<±5∘), the SNR also needs to be >65dBA, and Fr also needs to be flat to 10Hz to reduce noise effectively. All of these could make the passengers enjoy better music or phone call qualification. (Fig. 5)
Fig.5 Active noise reduction (ANC)
6. Voice recognition system
Due to the safety issue of driving, the traditional hand-operated interface has been replaced gradually by voice control. This technology uses the microphone to receive the driver's voice commands and translate them to interface commands to control the system. Usually, we can find it through devices like GPS navigators or audio systems.
In order to improve the recognition rate, the microphone will use an array structure to eliminate environmental noise effectively, thereby improving the accuracy of the interface control. The microphone needs to have phase consistency and Hi SNR characteristics. (Fig.6)
Fig.6. Voice recognition
7. Outside sounds monitoring
As an improvement of car vibration damping technology, the noise inside the car has been lower than before. Therefore, the emergency sound or the environment sounds might be easy to ignore. For safety reasons, microphones will also be installed out of the car to receive the ambient sounds. After that, DSP will calculate and distinguish the sound is meaningful or not and amplified to remind the driver. Then the driver could have enough time to avoid the accidents.
This kind of microphone's application must meet the requirements of IP6K9K to ensure it won't damage the characteristics during car washing or steam washing. (Fig. 7)
Fig.7 Car outside monitoring microphone (for the emergency situation)