The effects of a vertical reflection on the relationship between listener preference and timbral and spatial attributes

Early reflections play a large role in our perception of sound and as such, have been
subject to various treatments over the years due to changing tastes and room
requirements. Whilst there is research into these early reflections, arriving both
vertically and horizontally in small rooms regarding critical listening, little research
has been conducted regarding the beneficial or detrimental impact of early vertical
reflections on listener preference, in the context of listening for entertainment.
Two experiments were conducted through subjective testing in a semi-anechoic
chamber and listening room in order to assess subjects’ preference of playback of a
direct sound against playback with the addition of the first geometrical vertical
reflection. Program material remained constant in both experiments, employing five
musical and one speech stimuli.
Experiment one used a paired comparison method assessing a subjects’ preference,
and perceived magnitude of timbral and spatial difference provided by a frequency
independent ceiling reflection. Each comparison was followed by a free
verbalisation task for subjects to describe the perceived change(s). Experiment two
investigated this further by focusing specifically on subjects’ preference with a
frequency dependent reflection. A more controlled verbalisation task provided a list
of descriptive terms which the subject’s used to describe which attribute(s)
influenced their preference.
The results show that preference for playback with the inclusion of a vertical
reflection was highly varied across both subjects and samples. However both
experiments suggest that the main perceptual attribute with which subject’s based
their preference was timbre, common spatial attributes (image shift/spread) cannot
be used to predict preference. Experiment two suggests that the alteration of the
frequency content of a vertical reflection, may also provide a more consistent level
of preference for certain stimuli. It is also shown that while certain attributes occur
frequently (brilliance/fullness) for describing preference, others less frequently used
(nasal/boxy), may influence preference to a greater extent