An Acoustic Array for Undergraduate Instruction

We describe an acoustic array project and testbed for use in undergraduate instruction and research. The testbed consists of eight high-quality acoustic microphones connected to a programmable data acquisition system controlled by a laptop. The system is portable, allowing for outdoor data collections. The system can be used for collecting data that is processed off-line and can also perform real-time signal processing tasks. The project and hardware provide hands-on signals and systems experience for undergraduate students. 1. INSTRUCTIONAL GOALS As Electrical Engineering curricula evolve, there is a trend toward emphasizing signals and systems early in the program [1] and increasing design and teamwork experiences for undergraduates [2]. In keeping with this trend, we have developed a set of acoustic array projects centered around a hardware testbed. The main instructional goals of the microphone array project are: • to provide a hands-on hardware system for undergraduate students interested in signals and systems, • to provide team-oriented projects for undergraduate capstone design courses, independent study projects, and honors thesis projects within our department, and • to provide research experience to undergraduates, linked with existing graduate student research endeavors. In addition, we sought to provide a demonstration and data collection capability to support graduate research. A system that meets these goals must be flexible, modular, simple, and low cost. The system must be flexible enough to support a variety of student projects, yet be easy enough to use so that undergraduate students quickly come up to speed and make progress on projects. Finally, the system should be linked to our research program, to facilitate graduate student mentoring of undergraduates and to leverage faculty time. 2. THE MICROPHONE ARRAY TESTBED To meet these instructional needs and constraints, we have developed an acoustic microphone array system that includes data acquisition and processing capabilities. We developed a testbed that would support speech processing projects as well as outdoor vehicle localization and tracking problems. The outdoor data acquisition capability required that the system be portable. The hardware consists of eight microphones and preamplifiers, a portable National Instruments data acquisition unit, and a laptop computer whose functions are data storage, data acquisition control, and real-time signal processing. Eight Emkay BL 1994 microphones are used for acoustic signal acquisition. Each microphone is connected to a differential preamplifier and is fed into a National Instruments data acquisition system. The National Instruments hardware is housed in a SCXI1000DC chassis powered by a built-in 12-volt battery. The chassis contains an SCXI-1140 8-channel simultaneous sample-and-hold card to which the microphone outputs are connected, followed by an SCXI-1141 8channel programmable anti-aliasing filter. These cards have combined programmable gains up to 105. The signals are fed into a National Instruments AI16E-4 16-channel, 12-bit data acquisition card installed in a laptop computer. The data acquisition card can sample data and store it to the laptop hard disk at rates of up to 250 samples per second. The entire data acquisition system is lightweight and portable. The system weighs under 25 pounds and is housed in a 7 × 10 × 8 inch SCXI chassis cabled to a laptop. A photograph of the system is shown in Figure 1.