Evaluation of In-Car Communication Systems - Digital Signal Processing for In-Vehicle Systems and Safety - page 98

Fig. 5.20 Energy decay curves of the impulse responses at the listening person right ear
The ratio between the reverberation time of the turned-off and the activated system
describes the increase of the reverberation caused by the ICC system. The less the
reverberation time is increased, the better the quality of the system is. The reverbera-
tion time with an activated ICC system should not exceed a certain threshold which is
also depending on the type of the car. For example, a vehicle with only two seat rows
should not exceed a reverberation time of 80-150 ms (depending on the type of car).
5.5.2.2 Localization
The localization mismatch of the acoustical source is also one factor, which may
decrease the communication quality of the listening passenger. As mentioned before
in Sect. 2.2, this is correlated with the gain and the delay of the system as well as with
the location of the loudspeakers. Therefore, in any case, the loudspeakers which
support the correct localization of the acoustical source (e.g. loudspeakers located in
the rear side of the front seat) should be utilized by an ICC system.
Up to now, the evaluation of the localization quality can only be done by
subjective test methods. To perform an evaluation, a group of test subjects who
are educated in terms of acoustical analysis should experience the ICC system and
grade the localization impression.