Document ID: chunk:federal_register_of_legislation:F2021C00509:front:0:p42
Version: federal_register_of_legislation:F2021C00509
Segment Type: other
Provision Reference: 
Character Range: 123359–126145

shall be level; its surface shall be dry and so designed that rolling noise remains low.
          On the test site the variations in the free sound field between the sound source at the centre of the acceleration section and the microphone shall be maintained to within 1 dB. This condition will be deemed to be met if there are no large objects which reflect sound, such as fences, rocks, bridges or buildings, within 50 m of the centre of the acceleration section. The road surface covering of the test site shall conform to the requirements of annex 4.
          The microphone shall not be obstructed in any way which could affect the sound field, and no person may stand between the microphone and the sound source. The observer carrying out the measurements shall take up position so as not to affect the readings of the measuring instrument.

1.3.3. Miscellaneous

          Measurements shall not be made in poor atmospheric conditions. It shall be ensured that the results are not affected by gusts of wind.
          For measurements, the A-weighted sound level of sound sources other than those of the motorcycle to be tested and of wind effects shall be at least 10 dB(A) below the sound level produced by the motorcycle. A suitable windscreen may be fitted to the microphone provided that account is taken of its effect on the sensitivity and directional characteristics of the microphone.
          If the difference between the ambient noise and the measured noise is between 10 and 16 dB(A), in order to calculate the test results the appropriate correction shall be subtracted from the readings on the sound-level meter, as in the following graph:

1.4. Method of measurement

1.4.1. Nature and number of measurements

          The maximum sound level expressed in A-weighted decibels (dB(A)) shall be measured as the motorcycle travels between lines AA' and BB' (figure 1). The measurement will be invalid if an abnormal discrepancy between the peak value and the general sound level is recorded.
          At least two measurements shall be taken on each side of the motorcycle.

          1.4.2. Positioning of the microphone

          The microphone shall be located 7.5 m +/- 0.2 m from the reference line CC (see appendix-Figure 1) of the track and 1.2 m +/- 0.1 m above ground level.

1.4.3. Conditions of operation

          The motorcycle shall approach line AA' at an initial steady speed as specified in 1.4.3.1 and 1.4.3.2.When the front of the motorcycle reaches line AA' the throttle shall be fully opened as quickly as practically possible and kept in that position until the rear of the motorcycle reaches line BB'; the throttle must then be returned as quickly as possible to the idle position.
          For all measurements the motorcycle must