Standardized Automotive Audio Measurements
Since 2020, the Audio Engineering Society Technical Committee on Automotive Audio (TC-AA) has worked on developing an equipment specification and test methodology for in-car acoustic measurements that will ensure repeatable measurements, allow comparisons, and improve interpretation of results. This will make system-level specifications and requirements more meaningful and facilitate alignment between vehicle manufacturers (OEMs) and Tier 1 suppliers. In this paper, the TC-AA recommendations are demonstrated. The same test configuration is then used to demonstrate an extended suite of measurements that provides a more complete characterization of automotive audio. Measurements demonstrated in this paper include frequency response, seat-to-seat spectral uniformity, THD, intermodulation distortion, overall Max SPL, Max SPL at 10% distortion, and impulsive distortion.
Author: Steve Temme, Listen, Inc.
Presented at 9th ISEAT Conference (November 2024) Shenzhen, China
Summary
Standardized Automotive Audio Measurements
This paper by Steve F. Temme discusses a suite of measurements designed to characterize automotive audio systems. Temme’s work builds upon the Audio Engineering Society (AES) Technical Committee on Automotive Audio (TC-AA) White Paper, a document aiming to standardize in-car acoustic measurements.
The TC-AA white paper emphasizes several key aspects of measurement:
- Repeatable measurements, enabling accurate comparisons between different vehicles and systems.
- Clear interpretation of results, leading to more meaningful system-level specifications.
- Better alignment between vehicle manufacturers (OEMs) and Tier 1 suppliers, improving communication and collaboration.
Measurement Methods: The paper examines a range of measurements, including:
- Frequency response: This fundamental measurement assesses the system’s tonal balance by analyzing its output across the audible frequency range.
- Spectral uniformity: This measures how evenly sound is distributed across different seating positions, ensuring a consistent listening experience for all passengers.
- Distortion (THD, intermodulation): These measurements evaluate the system’s linearity, revealing potential issues like a poorly centered voice coil or crossover problems.
- Maximum SPL: This quantifies the system’s maximum volume, offering a valuable metric for both manufacturers and consumers.
- Impulsive distortion: This test identifies vibrations or rattles caused by speakers, ensuring the system’s proper installation and build integrity.
Test Setup: The paper describes a practical test configuration utilizing a six-microphone array, following the TC-AA recommendations. The setup includes:
- SoundCheck audio test system: Used for analysis and control.
- AmpConnect 621 audio interface: Converts microphone signals for the software.
- BQC-4149 Bluetooth interface: Transmits test signals to the car’s head unit.
Calibration: Accurate calibration is crucial for reliable results. This involves measuring microphone sensitivity with a calibrator and calibrating the audio interface for precise frequency and level responses.
The paper concludes by highlighting the increasing complexity of modern car audio systems and the need for standardized measurements. The TC-AA White Paper aims to establish a foundation for objectively evaluating these systems, facilitating comparisons and driving industry-wide improvements. The authors encourage feedback from the automotive audio community to refine the proposed methodologies and ultimately lead to a standardized industry approach.
