  All robots create consequential sound -- sound produced as a result of the
robot's mechanisms -- yet little work has explored how sound impacts
human-robot interaction. Recent work shows that the sound of different robot
mechanisms affects perceived competence, trust, human-likeness, and discomfort.
However, the physical sound characteristics responsible for these perceptions
have not been clearly identified. In this paper, we aim to explore key
characteristics of robot sound that might influence perceptions. A pilot study
from our past work showed that quieter and higher-pitched robots may be
perceived as more competent and less discomforting. To better understand how
variance in these attributes affects perception, we performed audio
manipulations on two sets of industrial robot arm videos within a series of
four new studies presented in this paper. Results confirmed that quieter robots
were perceived as less discomforting. In addition, higher-pitched robots were
perceived as more energetic, happy, warm, and competent. Despite the robot's
industrial purpose and appearance, participants seemed to prefer more "cute"
(or "kawaii") sound profiles, which could have implications for the design of
more acceptable and fulfilling sound profiles for human-robot interactions with
practical collaborative robots.
