Advanced Microphone Applications for Automotive

With the expansion of advanced automotive electronics, more and more product requirements exist. One microphone's applications are widely used, including the following application instructions.  (Fig. A)

1. Hands-free communication

2. Multi-area Hands-free communication

3. E-call

4. Driving recorder

5. ANC

6. Voice recognition system

7. Outside sounds monitoring

Fig. Microphone's application to automobile

 

1. Hands-Free communication

Hands-free communication was one of the first microphone applications in 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, its orientation angle is broad compared to the array microphone and 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 in the receiving 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. It could also strengthen the voice signal to improve the quality of communication. (Fig. 1)

Fig.1 Hands-Free System

 

2. Multi-area Hands-free communication

Many years ago, hands-free communication was only for drivers. Recently it has become for all passengers. In addition to the driving area, many microphones are installed in the passenger seat area. Microphones could be installed in the third row, even in larger cars.

In this way, all occupants in the vehicle can enjoy high-quality hands-free communication, and the system can automatically detect where the voice is. The system could also gain a group of microphones and attenuate the noise in the non-speech area, reducing the echo caused by the microphone and speaker in the car simultaneously. Furthermore, it improves 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

 

3. E-call

Many countries have included the car's E-call system in the mandatory regulations. Therefore, before the vehicles are sold to customers, they must have an E-call system to ensure that when an emergency occurs in the vehicle, passengers can quickly seek help from the service center.

An e-call system usually comprises a microphone, speaker, and DSP. It will be activated automatically when a car accident occurs. If the drivers or passengers speak directly with them, even in remote suburbs, they can immediately contact the service center to ask for help. The the microphone's sensitivity and signal-to-noise are 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)

Fig.3 E-call

 

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 received is usually not in specific directions, that is 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 vehicle, the microphone will need to prove an IPX6 or IP6K9K waterproof function. (Fig.4)

Fig.4 Driving recorder

 

5. ANC

When a car is running, besides the engine noise, there is friction between the tires and the 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, 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. These could make the passengers enjoy better music or phone call qualifications. (Fig. 5)

Fig.5 Active noise reduction (ANC)

 

6. Voice recognition system

Due to the safety issue of driving, voice control has gradually replaced the traditional hand-operated interface. This technology uses the microphone to receive the thdriver's voice commands and translate them to interface commands to control the system. We usually find it through devices like GPS navigators or audio systems.

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 High SNR characteristics. (Fig.6)

Fig.6. Voice recognition

 

7. Outside sound monitoring

As an improvement of car vibration damping technology, the noise inside the car has been lower than before. Therefore, emergencies or the environment might be easy to ignore. Microphones will also be installed outside the car to receive ambient sounds for safety reasons. After that, DSP will calculate and distinguish whether the sound is meaningful and amplified to remind the driver. Then, the driver will have enough time to avoid accidents.

This microphone application must meet the requirements of IP6K9K to ensure it won't damage the character won't during car washing or steam washing. (Fig. 7)

Fig.7 Car outside monitoring microphone (for the emergency)