ISO 6926:2016 音響 — 音響パワーレベルの決定に使用される基準音源の性能と校正の要件 | ページ 6

3.1

reference sound source

RSS

portable, generally electroacoustical or aerodynamic sound source or other noise-generating device, and associated control circuitry giving a broadband stable output complying with the requirements of this International Standard

3.2

free sound field over a reflecting plane

sound field in a homogeneous, isotropic medium in the half-space above an infinite, reflecting plane in the absence of other reflecting obstacles

3.3

hemi-anechoic room

test room in which a free sound field over a reflecting plane is obtained

3.4

reverberation test room

test room meeting the requirements of ISO 3741

3.5

measurement surface

hypothetical surface of area, S, on which the microphone positions are located at which the sound pressure levels are measured, enveloping the source under test and, in the case of a hemi-anechoic room, terminating on the reflecting plane on which the source is located

Note 1 to entry: The measurement surface area is expressed in metres squared.

3.6

surface sound pressure level

energy-average of the time-averaged sound pressure levels at all the microphone positions, or traverses, on the measurement surface, with the background noise corrections, K₁, applied at each microphone position or traverse

Note 1 to entry: Surface sound pressure level is expressed in decibels.

Note 2 to entry: For definition and calculation of K₁, see ISO 3745.

3.7

sound power level

L_W

Note 1 to entry: If a specific frequency weighting as specified in IEC 61672–1, and/or specific frequency bands are applied, this should be indicated by appropriate subscripts; e.g. denotes the A-weighted sound power level.

Note 2 to entry: This definition is technically in accordance with ISO 80000-8:2007,^[17] 8-23.

[SOURCE: ISO/TR 25417:2007, 2.9]

3.8

measurement radius

r

radius of a hemi-spherical measurement surface

3.9

directivity index

D_Ii

measure of the extent to which a source radiates sound in a particular direction, relative to the mean sound radiation over the measurement surface, where for fixed microphones, the direction is from the source to the position of the microphone, and for traverses, the direction is from the source to the position along the microphone path at which the highest sound pressure level is recorded

Note 2 to entry: With the above ”operational“ definition, the directivity index is a measure of the uniformity of sound radiation from the source over the particular measurement surface being employed and as it is installed in the test environment. Definitions for the “theoretical” directivity index appearing in textbooks and the literature usually represent the uniformity of sound radiation by comparing the source under test in its test environment to a point source of the same sound power radiating into a full sphere in a totally free field. When such definitions are applied to sources located in a free field above a reflecting plane, they include a constant “+3 dB” to account for the hemispherical radiation. Care should be taken when comparing or using different definitions of directivity index.

3.10

frequency range of interest

frequency range of one-third-octave bands with nominal mid-band frequencies from 100 Hz to 10 000 Hz

Note 1 to entry: The frequency range of interest in one-third-octave bands may be extended up to as much as 20 000 Hz or down to as low as 50 Hz, provided the requirements of this International Standard are still met.

3.11

comparison method

method in which the sound power level is calculated by comparing the measured sound pressure levels produced by the source under test in an environment with the sound pressure levels produced by a reference sound source of known sound power output in the same environment

3.12

direct method

method in reverberation test rooms where the sound power level is calculated using the equivalent sound absorption area determined from measurements of the reverberation time

3.13

reverberation time

T

time that is required for the sound pressure level to decrease by 60 dB after the sound source has stopped

Note 1 to entry: If the reverberation time is evaluated from the decay of the first 10 dB or 15 dB, it is denoted T₁₀orT₁₅, respectively.

Note 2 to entry: It is expressed in seconds.

3.14

repeatability condition

condition where independent test results are obtained with the same method on identical test items in the same laboratory by the same operator using the same equipment within short intervals of time