on the localisation in the superimposed soundfield - Hauptmikrofon ...

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1. Introduction
In the context of spatial hearing, BLAUERT 1974 defined the term “localisation” as
the mapping of the location of an auditory event to certain characteristics of a sound
event. If, based on BLAUERT 1969, the term “auditory event” is generally
understood to describe the “auditory perception determined by temporal, spatial and
other attributes” and the term “sound event” as the equally determined “physical
aspect of the listening process”, then initially one obtains an important descriptive
basis for investigations into spatial hearing.
During the course of this work, however, it has been found that as soon as more than
one sound source determines the properties of the ear signals, a more precise
definition of terms is required.
Under natural conditions, the listening process predominantly takes place in a
superimposed sound field. Normally, a multitude of interfering sources [e.g.
reflections from the floor or room boundaries (mirror sources)] but also equipollent
sound sources (e.g. different speakers in the vicinity of a listener) produce ear signals
that do not correspond in any way to the elementary case of a single sound source.
Yet, even under such sound field conditions, the human hearing system is capable of
“carrying out a very meaningful selection, ordering and grouping process” (PLENGE
1973), so that, despite the superposition, the auditory event mappings can be
accomplished. In this respect, two well-known auditory phenomena are the “law of
the first wavefront” (CREMER 1948) and the “cocktail party effect” (CHERRY 1953,
1954).
It appears that in the superimposed sound field the localisation mechanism relies on
underlying processes that are not directly applicable to the localisation of a single
sound source in a free sound field. These are all those processes that enable a separate
evaluation of certain ear signal components.
What are the ear signal components that the auditory system discriminates in the
superimposed sound field? Which characteristics of a sound event allow for this to
happen?
The literature is full of investigations addressing these two questions. Most notably,
this is the case for all studies into the phenomena of the “phantom source”, the “law of
the first wavefront” and the “cocktail party effect” (see BLAUERT 1974 for
references as well as the following sections of this thesis). Furthermore, investigations
in the area of binaural signal detection (see BLAUERT 1974 for references as well as
DOMNITZ / COLBURN 1976, 1977, HAFTER 1977, KOENIG et al. 1977, ALLEN
et al. 1977, HAWKINS et al. 1978, HAFTER et al. 1979) and some studies
concerning particular questions of auditory perception (e.g. see PLENGE 1973 for