GB/T 1859.1-2026Reciprocating internal combustion engines—Measurement of sound power level using sound pressure—Part 1:Engineering method (English PDF)

3.5 Measurement time interval; T

One or more operating period or operating cycle of the sound source being measured used to determine the time-averaged sound pressure level, in seconds (s).

3.6 Acoustic free field

An acoustic field where edge effect is negligible in homogeneous, isotropic media.

Note. The actual acoustic free field is an acoustic field where the reflection of edge or other objects within the frequency range of interest is negligible.

3.7 Reflecting plane

A flat surface for sound reflection on which the sound source being measured is located.

3.8 Acoustic free field over a reflecting plane

The acoustic free field in the half space over an infinitely large reflecting plane, without any other obstacles.

3.9 Frequency range of interest

The frequency range covered by the octave-band with a center frequency of 63 Hz~8000 Hz (1/3 octave-band of 50 Hz~10000 Hz).

3.10 Reference box

The smallest hypothetical rectangular hexahedron which envelops the sound source exactly and terminates on a reflecting plane (ground).

3.11 Measurement distance; d

The vertical distance between reference box and measurement surface of hypothetical rectangular hexahedron.

3.12 Measurement surface

An external surface of a hypothetical rectangular hexahedron for measuring the sound pressure level with an area of S, which envelopes sound source and on which measurement point is located. The measurement surface ends at the reflecting plane (ground).

3.13 Background noise

4.1 General

The test environment to which this Part applies is a room or outdoor flat space completely isolated from background noise, providing an acoustic free field over a reflecting plane; or a room or outdoor flat space, which is completely isolated from background noise and where reverberant acoustic field has limited effect on the sound pressure on measurement surface and environmental correction is available.

It shall avoid the adverse effects of environmental conditions on the microphone (such as wind, air flow, high or low temperature, etc.). It shall abide by the instructions of manufacturers of measuring instruments for adverse environmental conditions. Also, it shall take measures to ensure that any reflecting plane does not cause significant sound radiation due to vibration.

4.2 Background noise criteria

The time-averaged sound pressure level of background noise after averaging at microphone position shall be at least 6 dB lower than the uncorrected time-averaged sound pressure level of sound source being measured (unless otherwise specified, hereafter known as sound pressure level for short), and preferably at least 15 dB lower.

In frequency band measurements, not all frequency bands may satisfy the background noise criteria, even in test rooms where the background noise is low and well controlled.

For frequency band measurements, it shall, according to the following steps, judge whether the background noise criteria are met.

a) USE the sound power levels of all bands in the frequency range of interest to calculate A-weighted sound power level;

b) REJECT the frequency bands below A-weighted sound power level 15 dB or more (A-weighted) and deltaLp9 Recording content the following content, if applicable, shall be collected and recorded to measure as required by this Part.

a) Engine.

1) Description of the engine, including model, specifications (e.g., type, number of strokes, number of cylinders, cylinder bore, stroke, boundary dimensions, cooling mode; ISO standard power and corresponding rotational speed, etc.), number, manufacturer;

2) The type of fuel used and its octane or cetane number;

3) Diesel fuel injection timing (static and dynamic) or gasoline engine ignition timing (static and dynamic);

4) Base characteristics and the way in which the engine is connected to it (elastic or rigid);

5) The way in which the engine is connected to dynamometer equipment (elastic or rigid);

6) Installation conditions, including the height of the crankshaft center of the engine and the bottom of oil pan from the reflecting plane;

7) Description of auxiliary devices, including air filter, exhaust silencer (if any), cooling fan (if any), and acoustic enclosure (if any);

8) Engine power and corresponding rotational speed during noise measurements.

b) Acoustic environment.

1) Description of test environment (including physical descriptions of ground, wall, and ceiling, and sketches of the locations of sound source being measured and other objects);

2) Description of acoustic environmental appraisal in accordance with the Appendix A (Normative) Methods for appraisal of acoustic environment A.1 General this appendix specifies the method for measuring environmental correction K2 and can be used to evaluate the effectiveness of a given measurement surface of the sound source being measured.

The first appraisal test (absolute comparison method, SEE A.2) is performed using a standard sound source. This method is suitable for indoor or outdoor use; and is a preferred method for appraisal of test environment, especially when the frequency band data is required, and the sound source being measured can be removed from the test site.

The second appraisal test (according to room sound absorption method, SEE A.3) requires measuring the room sound absorption amount A. This test method is based on the following premises. The room shape is similar to a cube, is basically empty; and the room boundary has a sound absorption effect. Double-surface method and standard sound source method can be used to calculate room sound absorption amount A. If the sound source being measured cannot be removed or has a large size, one of the methods may be preferred.

A.2 Absolute comparison method the standard sound source whose characteristics meet the requirements of GB/T 4129 is placed on the ground of test environment. The center of the bottom surface coincides with the center of the bottom surface of reference box.

The measurement surface, microphone position and its number are the same as those of the sound source being measured. According to the provisions of Chapter 7, MEASURE the sound power level of standard sound source, without environmental correction (ASSUME K2=0).

Environmental correction K2 shall be calculated according to the formula (A.1).

Where.

LW* - Test environment sound power level of standard sound source, without ......