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Additional explanations for the changes and comments in the document „TFRA-03-10 Proposal for a new Regulation on Reverse Warning Devices based on decisions of 3rd TF on RA“ made by Ralf Hinnerichs of Grewus


  1. Background noise [page 5, 2.]


We suggest to add a definition of background noise or ambient noise which is used as a reference noise for comparing the alert signal with background noise. We recommend to regard this background noise as a homogeneous sound field in the measurement area around the warning device. This means that the SPL of the ambient noise is the approximately the same in the measurement area. 


  1. Definition of intermittent sound [page 7, 6.1.1]


In the informal document “GRB-68-25 status report to GRB #68” on page 7 the importance of allowing freedom of design of the warning sound has been stated and that the TF does not intend to exclude warning sounds by sound quality. With this background, the “clock of the interruption” should also consider sounds like „sh-shhh – pause – sh-shhh“.                


  1. Specifications of the sound characteristics [page 11, 6.3.7]


According to DIN 7731 the sound of a warning device can be regarded as clearly audible if certain conditions are met, our suggestion is to follow this concept.


To avoid hearing impairment, a maximum for the overall SPL of the warning sound should be given. According to several medical sources the maximum level of sound for short time pulses is 120dB. If the sound level is higher, hearing impairment will be the result.


  1. Specifications of the position of audible reverse warning devices in motor vehicles [page 15, 14.]  


In our opinion the reasonable position of the audible reverse warning device should be taken into account.  The audible reverse warning device should be mounted within the last rear meter of the vehicle and it should be switched off if this is not met. This considers vehicles with a trailer, where a warning device between the vehicle and the trailer would not be useful for warning but would cause noise pollution.