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Abstract
As new technologies appear, the expressive palette of creators broadens. Parametric loudspeakers are one of such new technologies that makes it possible to direct sound as though it were a light beam. Since their debut in the market, they have thus far received little attention from part of the artistic world. Some peculiarities concerning the sound reproduction might explain why musicians in particular are hesitating to use an otherwise highly attractive acoustic innovation. Due to such peculiarities, a proper use of parametric loudspeakers in art must start with investigating a whole array of different topics (i.e. non-linear acoustics and ultrasonic transducers) in order to understand how this technology works and utilize it at its best. The result of our project is ultimately a sound installation that makes use of directional sound to ruminate on issues concerning sound perception and the responsible use of our sound environment.
Acknowledgements
The authors wish to thank Rodrigo Henao for helping to collect data during measurements. They wish to thank also Dr Paolo Bientinesi, Dr Daniel Sierra and the anonymous reviewers for their insightful comments to the preparatory version of this article.
Notes
1 The expression ‘end-fire array’ comes from the antenna theory and describes a specific kind of emitters configuration used to maximize radiation along the main axis of the antenna. The same expression is used as an analogy in the theory of parametric loudspeakers since, as it will be explained further on in the text, they behave in a similar way.
2 More modulation schemes have been tested since then, e.g.: modified amplitude modulation, and quadrature, recursive and hybrid modulation methods (Gan & Ji, Citation2010).
3 THD as well as poor performance in the low spectrum of audible frequencies may be real issues at the moment of using this kind of loudspeaker. Both aspects will be discussed in Section 6.
4 As mentioned in note 2, such a major problem, in particular with regard to music reproduction, will be addressed in Section 6.
5 Gan et al. set the cut-off frequency at 1000 Hz. No laboratory measurements are needed to claim that, at least with an Audio Spotlight® as the one we used (the AS-24i), frequencies lower than 1000 Hz can be clearly heard that are not the by-products of a missing fundamental effect. After some measurements, we decided to set the cut-off at 400 Hz, as it is also suggested by Holosonics.
6 As early as Citation1983, Yoneyama and Fujimoto suggested using these ‘acoustic spotlights’ in museums, exhibits or any place where building sound barriers would be too expensive and unnecessary.
7 The title is a reference to Stéphane Mallarmé’s poem of the same name.
8 In fact, the space where the prototype was first exposed—the front foyer of our University’s Humanities School—contains four concrete columns and other concrete structural elements.
9 A video of the setup can be watched at https://www.youtube.com/watch?v=QGJGeWxAMVw.
10 Also Holosonics seems to be claiming the same when it says that its larger speaker (the AS-24i we used) has an extra low octave range with respect to the other two, smaller models (the AS-168i and the AS-16i).
11 The experiments carried on by the authors deserved a much larger amount of testers than the only eight subjects who actually took part in them.
12 Nonlinearity can be quantified by a single value known as parameter of non-linearity. In diatomic gases like air at a temperature of 293.15 K (20 °C) that value is 0.4. At this same temperature, the velocity is 343.2 m s−1.