Standards Development

Scope

This document specifies the precision method for hemi-anechoic rooms, which is the measurement method of the sound power level for reciprocating internal combustion engines. This document applies to all reciprocating internal combustion engines falling within the field of application of ISO 3046-1 and other internal combustion engines where no suitable International Standard exists.

Purpose

1)For user's convenience, the series standards of ISO 6798 Reciprocating internal combustion engines — Measurement of sound power level using sound pressure has been proposed corresponding to the basic referenced standards ISO 3744, ISO 3745, ISO 3746 and ISO 3747, which contains four parts— Part 1: Engineering method, Part 2: Survey method, Part 3: Survey method for use in situ and Part 4: Precision method for hemi-anechoic rooms. The development of Parts 1, 2, and 3 has been completed. The proposed Part 4 serves as a supplement to the ISO 6798 series, constituting a new development. This part will fill the gap in international standards for the precision method using hemi-anechoic rooms in the field of internal combustion engines, improving the system for determining sound power levels using sound pressure to meet the needs for measuring engine noise in various acoustic environments.

2)With the development of productivity, global demand for engines remains stable and substantial. While power and fuel economy continue to improve, the ongoing optimization of engine noise levels is also essential for the healthy development of the industry. Noise regulations related to engines across various global sectors are becoming increasingly stringent; for instance, the latest update to EU Regulation ECE R51 in July 2024 tightened requirements by 1-2 dB(A) overall.

3)To further reduce the impact of background noise corrections and environmental corrections on measurement results, improve accuracy grade, and reduce misjudgments, an increasing number of engine tests now conduct noise measurements in hemi-anechoic rooms, particularly for engine R&D testing and acceptance testing. However, there is currently no corresponding measurement standard. Therefore, it is necessary to establish a specific standard for engine noise measurement in hemianechoic rooms—the Precision Method (Grade 1 accuracy). This measurement standard can be used for acceptance tests and calibration tests, as well as for acoustic design and development.

4)ISO 3745 is a fundamental international standard without application rules specific to particular test objects. It lacks clear provisions for engine installation and operating conditions, making it unsuitable for direct user guidance. The proposed ISO 6798-4 (Grade 1 accuracy) will provide explicit specifications for microphone array positions, the installation of engine accessories and auxiliary equipment, and operating conditions. This will offer more targeted testing guidance for users of the standard.