Hindawi Publishing Corporation ISRN Mechanical Engineering Volume 2013, Article ID 241958, 11 pages http://dx.doi.org/10.1155/2013/241958 Research Article Scan and Paint: Theory and Practice of a Sound Field Visualization Method Daniel Fernández Comesaña, 1,2 Steven Steltenpool, 1 Graciano Carrillo Pousa, 1 Hans-Elias de Bree, 1 and Keith R. Holland 2 1 Microlown Technologies, Tivolilaan 205, 6824 BV Arnhem, he Netherlands 2 Institute of Sound and Vibration Research, University of Southampton, Southampton SO17 1BJ, UK Correspondence should be addressed to Daniel Fern´ andez Comesa˜ na; fernandez@microlown.com Received 23 June 2013; Accepted 24 July 2013 Academic Editors: Y. Chen and Y. Zhang Copyright © 2013 Daniel Fern´ andez Comesa˜ na et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Sound visualization techniques have played a key role in the development of acoustics throughout history. he development of measurement apparatus and techniques for displaying sound and vibration phenomena has provided excellent tools for building understanding about speciic problems. Traditional methods, such as step-by-step measurements or simultaneous multichannel systems, have a strong tradeof between time requirements, lexibility, and cost. However, if the sound ield can be assumed time stationary, scanning methods allow us to assess variations across space with a single transducer, as long as the position of the sensor is known. he proposed technique, Scan and Paint, is based on the acquisition of sound pressure and particle velocity by manually moving a P-U probe (pressure-particle velocity sensors) across a sound ield whilst ilming the event with a camera. he sensor position is extracted by applying automatic color tracking to each frame of the recorded video. It is then possible to visualize sound variations across the space in terms of sound pressure, particle velocity, or acoustic intensity. In this paper, not only the theoretical foundations of the method, but also its practical applications are explored such as scanning transfer path analysis, source radiation characterization, operational delection shapes, virtual phased arrays, material characterization, and acoustic intensity vector ield mapping. 1. Introduction In the development of acoustics, sound representations have been thought of as a key to aid in its understanding. he necessity to represent sound and vibration information visually triggered many investigations with a common goal: to create tools to build intuition and understanding upon speciic problems. Many alternative methods and apparatus have been proposed over time [1] as is addressed in the following section. Nevertheless, the current measurement procedures for characterizing sound ields can be classiied by three major categories, regardless of the postprocessing techniques applied: step-by-step, simultaneous, and scanning measure- ments. Each of these techniques can be evaluated simply using three main features: measurement time, lexibility, and total cost of the equipment. Step-by-step is the most common technique to create spatial representations of stationary sound ields. It is based upon the acquisition of data at a set of discrete positions. he lexibility of this method is one of its main advantages since the number of transducers and their spatial distribution are completely customizable. he number of sensors used is directly related to the cost of the equipment but inversely pro- portional to the time needed to undertake the experiments. In the case that all positions are characterized at the same time, it is necessary to use of a large multichannel system, hence to perform simultaneous measurements. Measurement solutions based upon sensor arrays con- ventionally imply a large cost and low lexibility derived from their complexity. An intermediate solution, able to reduce the measurement time without increasing the equipment cost, can be found by using scanning methods. Scan-based techniques have a fundamental diference to the previously