scope:

This Standard specifies an alternative test procedure to produce horn sound level data equivalent to that produced by the in situ procedure in 49 CFR Part 229.129.

This method may be used when:

1. No test location exists that meets the requirements of the regulation.

2. A conforming location exists but testing at that location creates an unacceptable environmental impact on the surrounding residents.

3. The standard is applicable for a specific locomotive model, horn model, and mounting location and for horns having a fundamental frequency between 200 Hz and 4,000 Hz.

Three separate measurements are specified to produce results that are acoustically valid and to determine the transfer function: measurement of the maximum and minimum compressed air pressures for the fleet, measurement of the A-weighted sound level of the horns under test in situ, and measurement of the horn in a hemi-anechoic room. Once the transfer function is determined, only measurements in a hemi-anechoic room are needed to produce horn sound levels to evaluate compliance with the Federal requirement.

In addition, this method relies on an a priori knowledge of the effect of the horn mounting position on the train. A procedure is specified to determine this transfer function on a typical sample of trains.

The test procedure relies on mounting the horn under test in a hemi-anechoic room provided with a compressed air supply. Previously determined maximum and minimum air pressures measured during horn soundings are used to test the horn acoustical output.

A-weighted data are used in the evaluation of horn output and mounting transfer function to permit adjustment of the acoustic output measured ex situ in a hemi-anechoic room to correspond with the level that would be measured in situ by the FRA test method. The A-weighted adjusted levels are then reported per the FRA requirements.