BS ISO 9921-1:1996

1 Scope
2 Normative references
3 Definitions
    3.1 Speech communication
    3.2 Speech intelligibility
    3.3 Vocal effort
    3.4 Speech interference level
    3.5 Lombard effect
4 Symbols
5 Determination of noise parameters
    5.1 General
    5.2 Equipment for measurement
    5.3 Microphone positions
    5.4 Time-averaging
    5.5 A-weighted sound pressure level at the speaker's
          position
    5.6 Speech interference level
6 Criteria for direct speech communication
    6.1 Vocal effort of the speaker
    6.2 Speech level at the listener's position
    6.3 Relation between speech interference level and
          communication distance (SIL method) for
          satisfactory speech intelligibility
    6.4 Additional assessments of the quality of speech
          communication
    6.5 Use of hearing protectors
Annexes
A Selected values of median hearing threshold deviations
    for males up to 70 years of age (octologically
    normal persons) in accordance with ISO 7029
B examples of the use of figures 1 and 2
C Bibliography

Supplies a method of predicting the effectiveness of speech communication where machinery or other noise is present. Gives a method of assessing direct speech communication in the following situations: 1. Ambient noise at the speaker's or listener's position. 2. Vocal effort. 3 Distance between the communication partners.