Motor Racing Vehicles - Measurement Methods

Motor Racing Vehicles - Measurement Methods

6 Proposal for new methods

6.1 Declaration method
6.2 Monitoring method

6.1 Declaration method

Based on the above analyses, the following noise declaration method is proposed based on 1/1-octave band levels:

L_w = L_eq,t + 10 log 4vat - ΔL_gd - 10 log N, where

L_W is the energy equivalent immission relevant sound power level per 1/1-octave frequency band in dB re. 1pW.
L_eq,t is the energy equivalent sound pressure level per 1/1-octave frequency band in dB re. 20µPa measured over an integration time interval t.
v is the average passby driving speed in m/s.
a is the shortest distance from the microphone to the centre line of the track. The distance from the microphone to the individual vehicle may vary within ±10%.
t is the integration time in seconds.
N is the number of passbys.
ΔL_gd is the ground correction for declaration purposes, defined in Table 1.

This method gives the average immission relevant noise emission for one vehicle. The microphone position shall be chosen at a straight section of the track, where the vehicles yield maximum engine power, e.g. after a curve. The measurement section shall be as long as possible, preferably 10 times the measurement distance a, which shall be in the range 4-10 m. There shall be no significant sound reflecting or screening obstacles close to the measurement area. The microphone shall be 1.5-1.8 meters above the ground. In case of measurement of noise from speedway motorcycles, the microphone shall be placed above the security fence around the track, and likewise 1.5 m to 1.8 m above the track surface.

Click on the picture to see the html-version of: ‘‘Table 1‘‘

Table 1 shows the ground corrections as defined for 3 typical racetracks. Measurements performed on soil tracks and gravel tracks shall be done over an acoustically soft surface, e.g. grass or soil.

Measurements on asphalt tracks can be made with the microphone positioned above either an acoustically soft surface or a hard surface. The values for Asphalt tracks/hard surface are however based on noise measurements from only one vehicle.

As shown in ref. 2, the primary variable regarding measurement uncertainty is the number of passbys. With N = 30, the uncertainty may be estimated at 3 dB, given as a 90% confidence level.

For measurements of new declaration values at least 30 passbys from at least three different vehicles shall be measured and averaged on an energy basis. The passbys shall be evenly distributed between the vehicles and representative vehicles shall be used.

6.2 Monitoring method

Based on the above analyses, the following noise monitoring method is proposed, based on measurement of A-weighted maximum levels:

L_WA = L_pAmaxF + 10 log(4 ð a² ) - ΔL_g

L_WA= L_pAmaxF + 20 log a + 10 log(4 ð) - ΔL_g

L_WA = L_pAmaxF + 20 log a + ΔL_gm, where

L_WAis the energy equivalent immission relevant A-weighted sound power level in dB re. 1pW.
L_pAmaxFis the maximum A-weighted sound pressure level dB re. 20µPa, measured with integration time FAST.
a is the minimum distance between the individual vehicle and the microphone in m.
ΔL_gm is the ground correction for monitoring purposes, defined in Table 2. For simplicity reasons ΔL_gm = 10 log(4 ð) - ΔL_g.

This method gives the A-weighted immission relevant noise emission for one specific vehicle. The microphone position shall be chosen at a straight section of the track, where the vehicles yield maximum engine power, e.g. after a curve. The measurement distance a shall be in the range 4-10 m. There shall be no significant sound reflecting or screening obstacles close to the measurement location. The microphone shall be 1.5-1.8 meters above the ground. In case of measurement of noise from speedway motorcycles, the microphone shall be placed above the security fence around the track, and likewise 1.5 m to 1.8 m above the track surface.

Click on the picture to see the html-version of: ‘‘Table 2‘‘

Table 2 shows the ground corrections as defined for three typical racetracks. However, in order to facilitate monitoring measurements at asphalt tracks, a correction for microphone positions above a hard surface has been included.

As shown in ref. 2, the primary variable regarding measurement uncertainty is the number of passbys. With N = 4, the uncertainty associated with the average value of L_pAmaxF, and thereby L_WA, may be estimated to 4 dB, given as a 90% confidence level. It is therefore recommended that monitoring shall be based on the average value of 4 passbys, as the result based on e.g. a single passby may be too uncertain.