6.1 Overview of the U.S. NPRM on QRTV

The NPRM was not yet published and therefore its presentation and subsequent discussion was postponed to a future meeting.

6.2 Overview of current U.S. testing

NHTSA (supported by its VOLPE Centre staff via Audio) presented an overview of its recently published research report on the development of sound specifications for EVs and HEVs (GTRQRTV-01-10e). The findings may be reflected in the NPRM.

It revealed that a wide spectrum of 1/3 octave bands must be considered when creating an artificial sound that is qualified to make quiet vehicles acoustically recognisable in urban traffic, ranging from 315 Hz centre frequency at the lower end up to 5000 Hz. In order to determine the necessary sound pressure levels of the individual 1/3 octave bands, a background noise level of 55 dB(A) is assumed. A rational for the magnitude of the background level could not be given at this time and NHTSA referred to a time after the publication of the NPRM. ISO questioned if it was possible to exclude some of the 1/3 octave band in the case that other bands had a higher level. NHTSA stated that this might be possible but due to a lack of statistical robustness, such an approach could currently not be confirmed. Volpe mentioned at several occasions that more data from industry would be highly appreciated as the available test results may not be sufficiently informative to work out adequate proposals for acoustical requirements. Results considered so far are based on data received from OICA in 2011, where industry was asked to deliver whatever data was available. This was delivered in an unstructured manner so that the data is somewhat unfocussed on specific results. Seen the weak robustness of the elaborated results, VOLPE signalled flexibility in terms 1/3 octave bands and their individual sound pressure levels.

OICA requested justification for the requirement of frequency content below 400Hz. VOLPE stated that is necessary in order to let the vehicle sound as an ICE. OICA raised concerns of annoying perceptibility inside the vehicle, as this effect becomes more and more significant with the decrease of frequencies . Technically it is increasingly difficult if not impossible to attenuate frequencies below 400Hz emitted by a speaker being installed in a vehicle. Sounds below this frequency will transmit into the vehicle. Effectively this risks leading to serious customer complaints up to the rejection of technology. VOLPE was not aware of this concern but is willing to investigate. However, measurement data is necessary and Industry is asked to support.

OICA also pointed out the possibility of a single speaker system not being the adequate technology to produce the proposed sound pressure levels of a frequency range as large as currently under investigation. This may require more sophisticated systems, such as a combined system consisting of one piezoelectric element and a conventional speaker, with adverse consequences of increased costs, difficulties in packaging due a higher installation space as well as a negative weight impact.

OICA also mentioned that data is taken from many different vehicles and questioned if all of them are qualified to contribute to the determination of a typical ICE sound characteristic. If frequency content from both loud and decent vehicles is averaged with 4-/6- and 8 cylinder engines, the result is not necessarily representative for ICE vehicles.