Active Noise Cancellation System: Overview Cadillac SRX II facelift

Scheme 56

Circuit/System Description

The Audio Amplifier receives a discrete pulse-width modulated engine speed signal from the Engine Control Module. The Audio Amplifier uses the engine RPM signal for operating active noise cancellation.

The active noise cancellation system uses three microphones in the vehicle headliner: one above each front seating position, and one above the rear seat. The Audio Amplifier provides a bias voltage to each microphone (+) and (-) signal circuits for operation of the microphone. The microphones monitor the vehicle cabin for undesirable engine sounds. The Audio Amplifier uses the microphone inputs and an engine RPM signal to determine the frequency of the undesirable sound.

Active Noise Cancellation Description and Operation

The entertainment system on this vehicle may have several different configurations. To determine the specific configuration of the vehicle, please see the Service Parts ID Label, and refer to RPO Code List.

Scheme 57

The main components of the Active Noise Cancellation system are

1. 3 microphones in the vehicle headliner.
2. A discrete engine speed (RPM) signal from the engine control module to the amplifier
3. Active Noise Cancellation electronics and software integrated into the audio amplifier
4. The vehicle speaker system, connected to the amplifier, to output the desired cancellation frequencies

The Active Noise Cancellation system is operational under the following conditions

1. The amplifier has passed all self diagnostic checks
2. All doors are closed
3. Battery voltage is between 9.5 V and 16 V
4. The vehicle cabin temperature is less than 140°F (60°C)
5. Engine speed is between 550 and 3000 RPM

The Active Noise Cancellation system is a method used to reduce the perception of certain undesirable sounds generated by the engine into the vehicle cabin. The systems uses microphone and engine speed signals, software integrated into the amplifier, and the vehicle speakers to determine and generate the correct frequencies needed to achieve the desired reduction.

Three microphones are located in the headliner to monitor noise/sounds in the vehicle cabin, and are directly connected to the amplifier. The amplifier also receives a discrete engine speed (RPM) signal from the engine control module. The amplifier processes these inputs to determine the frequency of the undesirable sound. The amplifier then calculates the appropriate cancellation frequency and outputs a cancellation signal (audio tone) to the vehicle speakers to reduce the perception of undesirable sounds by the vehicle occupants so the vehicle cabin appears quieter and without vibration.

See also:
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