Acoustics Class Research Articles

An inexpensive teaching laboratory apparatus for measuring the speed of sound and more

One of the laboratory experiments in our general education acoustics class is a measurement of the speed of sound activity. The apparatus for this activity consists of a pair of ultrasonic transducers, a signal generator, and an oscilloscope. Each transducer is mounted on a custom base that is designed to rest on top of a standard meter stick which lays flat on the lab bench. The bases are arranged on the meter stick such that the transducers face each other. One of the transducers is driven by the signal generator at its resonance frequency, creating a sound wave which is detected by the other transducer. By monitoring the relative phase of the transmitted and detected sound wave signals, an accurate measurement of the wavelength of the sound can be obtained. From the wavelength measurement and the drive frequency students easily calculate the speed of sound in the room. With the advent of 3D printing and the availability of inexpensive signal generators and oscilloscopes, this apparatus is affordable not only for colleges but also to many high schools. Furthermore, the apparatus can be also used to explore other wave phenomena, such as reflection, absorption, and interference.

Measuring and analyzing sound using phone microphone and free software

In Fall 2022 acoustics class, the students developed class projects using their smart phones to measure sound. In a laboratory exercise, the phones were calibrated against a standard microphone. A microphone circuit was bread boarded and calibrated to demonstrate the inner workings of electret microphone technology. Students developed projects around the measurement of sound, including measuring striking a cymbal, analyzing piano chords, analyzing guitar chords, characterizing reverberation time in a warehouse, and determining the amplification from a 3D printed human ear and bat ear. The sound files from the phone were edited to isolate the relevant sound and converted to WAV files using Garageband software. The WAV files were imported into Python for post-processing, such as windowing, filtering, and FFT. Most projects used a waterfall plot to demonstrate some time-frequency analysis. The ease with which the students mastered sound measurement and processing led to unexpectedly mature projects. The low cost of the equipment makes this approach a widely deployable educational paradigm.

Using the mechanical waves concept survey in a non-majors acoustics class

The Mechanical Waves Concept Survey (MWCS) is a concept inventory designed to identify common misconceptions specifically related to Waves and Optics. It is a 22 question multiple choice assessment designed to be given pre and post instruction. The development of this inventory involved many revisions and administering the test to hundreds of students ranging from high school to university students in several different countries including Mexico, Thailand, and Australia. The use and effectiveness of the MWCS in other settings such as America, community colleges and non-majors courses have not been thoroughly examined. This presentation will outline results for an American community college specifically for students who are not intending to be STEM majors. Several semesters of assessment data will be presented. Due to the change in instruction modality during COVID, a comparison between delivery methods, in person and online was examined. Future work regarding improvements to the concept inventory will be discussed.

Blackstock 9-3: Spherical waves, reflection, and attenuation

One of my favorite homework problems for waves in fluids or a general acoustics class is Blackstock 9-3, which involves a submarine positioned 50 m below the ocean surface and 500 m above the seafloor. The problem asks students to calculate the impedance of the seafloor given a frequency and known sound pressure levels received by the submarine after bouncing off the ocean surface or the seafloor. In part a, the calculation is made assuming a lossless medium and then in part b, using attenuation. The reasons this is one of my favorite problems are that it is real-world derived, combines many concepts, and requires understanding of wave propagation physics to solve; there is no simple equation (that I have found at least) that will immediately provide the correct answer. Students often struggle with what type of wave is emitted (plane versus spherical), then, if spherical waves, how to account for the boundary—especially on the seafloor where one must calculate the reflection coefficient. Every year this problem allows for good discussion in class and homework review sections.

Calculating the acoustic input impedance of a simplified brass instrument as an educational laboratory activity

The concept of acoustic impedance is often difficult for students in introductory acoustics courses to make sense of, especially students without advanced mathematics backgrounds. This work summarizes a laboratory activity for students in a general education musical acoustics class where a simplified brass musical instrument is examined, focusing on how the geometry of the air column affects the input impedance of the instrument. Students are guided through making bore profile measurements for use in a computation of the input impedance. Options for making experimental measurements of the simplified instrument are explained. The laboratory activity was successfully used with students who reported their increased understanding of the acoustics of brass musical instruments.

Reflecting on universal design for learning in hybrid and in-person acoustics education

When transitioning to remote (Spring 2020) and hybrid (2020-21 academic year) learning during the COVID-19 pandemic, educators worked quickly to make lectures, coursework, and assessments accessible remotely. As educators return to in-person instruction, accessibility has become an even more essential and evolving part of effective course design (Kim, 2021). The Universal Design for Learning (UDL) Framework aims to maximize learning for all students through flexibility and choice (CAST, 2018). However, to broaden UDL’s impact, these strategies should be transparent to students (Super et al., 2020). This presentation will discuss the use of exam wrappers for students to reflect on UDL practices and their own learning in an undergraduate acoustics class. Exam wrappers are a reflective exercise where students analyze their study strategies after a summative assessment (Lovett, 2013). We will present how UDL practices were implemented in a Speech Science course. Then, we will review lessons learned from using a custom exam wrapper where students reflect on their study habits after exams that assess their application of anatomy and physiology to speech acoustic output. The exam wrapper also aims to obtain formative feedback on UDL practices. This work can inform strategies for UDL implementation and student reflection in acoustics education.

A measurements laboratory built around a digitally-sampled microphone circuit

In Fall of 2017, a series of measurement laboratory exercises, built around a microphone preamplifier and filter, were used in teaching an engineering measurement techniques course. The microphone circuit included a preamplifier that introduced JFETs, a virtual ground and buffer to illustrate loading effects, a high pass filter and a low pass filter, and a zener-diode-based limiter. The data were sampled using a beaglebone microcontroller's built-in analog-to-digital converter. The data was transmitted to matlab for post-processing and analysis. The microphone was then used in the Spring 2018 acoustics class. A variety of projects, including a Kundt’s tube, a driven closed-open pipe, a 3D printed horn for a blue-tooth speaker, and an absorptivity measurement for a restaurant’s wall treatment tiles, were completed in the course. It was observed that students showed improved interest in the material (increased in-class and out-of-class questions about specifics of the course material related to the project, increased exploration of material outside the provided course materials, full participation by all members of the class in the project) and learning (improved test scores after the project began relative to scores before the project began) relative to earlier classes where no experimental component was included.

Implementing electronic speckle pattern interferometry for a variety of activities in a general education acoustics class

A familiar acoustics laboratory experiment is finding Chladni patterns using flat plates of various geometries. Another method used in musical acoustics to find mode shapes of vibrating objects is electronic speckle-pattern interferometry (ESPI). We introduced students in a general education acoustics class to ESPI in addition to the traditional Chladni plate laboratory activity. A variety of ways to implement ESPI in the class were developed including: comparing traditional Chladni patterns to ESPI, examining traditional musical instruments with ESPI, and an advanced investigation of a well-known acoustics demonstration. A classic acoustics demonstration is rubbing the rim of a wine glass to create a musical tone. A coffee mug, unlike a wine glass, has an asymmetry due to the mug handle. ESPI can be used to study the effects of filling the mug with water in terms of the mug’s natural frequency, amplitude, and mode shapes. Results from ESPI showed that the mode shapes do not change with the addition of water. Filling the coffee mug with water lowered the natural frequencies of the lowest modes in a manner similar to that of a wine glass.

Bringing Matlab into the acoustics class

The Catholic University of America has a history of graduate education in acoustics that ranges back to the 1930s. Many of the students served by CUA have been and continue to be working professionals in careers related to acoustics. Over time, we have observed that many of our students come to us having developed an impressive depth of knowledge in their specialty. However, some of these students have little of the formal acoustics training needed to provide broader context. This presentation will discuss teaching practices designed to serve this cohort as well as more traditional graduate students. We create an experiential learning environment that capitalizes on the fact that many simple but powerfully instructive measurements can be made with now ubiquitous items. All modern laptops have both speakers and a microphone. A laptop, coupled with a library of MATLAB code, gives students the opportunity to explore many important topics. This presentation includes examples from room acoustics, musical acoustics, and elastic wave propagation.

Genealogy of Kenneth N. Stevens and the Speech Communication Group at the Massachusetts Institute of Technology

Ken often told a story to his advisees, illustrating how a seemingly insignificant event could change the course of a life. When Ken began his graduate studies at MIT, Leo Beranek learned that he had taken an acoustics class as an undergraduate and recruited him as a teaching assistant. Beranek was doing research on speech acoustics, and soon Ken was one of his research assistants. Thus, Ken’s decision to take an undergraduate acoustics course led him to his lifetime of work in speech communication, in which he found boundless pleasure. After completing his Sc.D. in 1952, Ken joined the MIT Faculty. His first doctoral student was James Flanagan. He supervised at least 31 more doctoral students and scores of post-doctoral, masters, undergraduate, and visiting students over 53 years. Ken collaborated with MIT colleagues (e.g., Morris Halle and Jay Keyser, Linguistics Dept.) and many researchers well beyond 77 Massachusetts Ave (e.g., Gunnar Fant, KTH, Sweden). His interest in how the physics of the vocal tract interacts with contrastive phonological categories unequivocally changed the field of Speech Communication, as well as the lives of his many students and collaborators who have gone on to establish their own laboratories and research programs.

Teaching advanced undergraduate students principles of outdoor sound propagation using football game measurements

As part of a sound system evaluation at Brigham Young University’s football stadium and to assist in planning for future system design, measurements were made before and during games by an upper-level undergraduate acoustics class. The measurement experience provided significant training opportunities for the students. Teams of students used sound level meters to make recordings at numerous locations both inside and outside the stadium. These measurements were then correlated with data from stationary microphones placed near the field. From the data, the predicted slow, A-weighted equivalent levels in and around the stadium were calculated relative to an assumed 90 dBA on the sideline. Straightforward outdoor sound propagation prediction methods involving geometric spreading, atmospheric absorption, barriers, etc. were successfully used to validate the measured data within 1-2 decibels at many locations, including a location in the foothills to the southeast of the stadium at a distance of approximately 3 km. The students appreciated the hands-on experiences gained by participation in the measurements and analysis.

Acoustics at Berklee College of Music and elsewhere

Students in the acoustics class at Berklee College of Music were non-science majors, but the course has done well, spanning over 50 semesters, and a number of those students have continued into graduate school and careers in acoustics. This paper will focus on the design and goals of the class, and will also discuss related experiences of teaching non-scientists in seminars, short courses, courses at other colleges, and the ASA-sponsored Continuing Education short course for architects.

Providing interactive engagement in introductory acoustics through design-intensive laboratories

More than three decades worth of education research has shown with overwhelming evidence that the best way for students to learn is to be actively engaged in the classroom rather than passively taking in material delivered from an instructor. Although the reform of introductory classes has been widely adopted by many instructors, the implementation of reformed introductory laboratory curricula has not been as widely adopted. In our introductory acoustics course, students complete design-intensive labs where much of the instruction has been stripped away. The emphasis on student-driven experiment design and analysis is intended to provide a more scientifically authentic experience for students. The course is taught using an integrated lecture and laboratory approach. An overview of the laboratory framework and example laboratory activities used in our introductory acoustics class will be presented.

Introducing the concept of resonance to non-science majors in a musical acoustics class

Understanding the concept of resonance is one of the most important goals for a student in a musical acoustics course to achieve. In our musical acoustics course students examine the standing wave behavior of simple one-dimensional systems such as stretched strings and pipes with open ends or one closed end. The concept is integral to the discussion of how nearly all musical instrument work, but it is also a difficult concept for many students to understand. In our class, we discuss how looking at the boundary conditions of the systems we examine in class can be applied to predict what the resonant frequencies of the system are.

Active-learning techniques in an introductory acoustics class

The goal of active-learning techniques is to encourage the students to become involved with the material and take ownership for their learning, which fosters long-term knowledge and enjoyment of the subject. In this era of student-based learning outcomes, an active-learning approach is important because it focuses on what the students are doing to facilitate learning instead of what the instructor is trying to teach. To benefit most from class time, the students need to have the opportunity to actively engage with the material beforehand. If meaningful pre-class activities are required, it is easier to interact with the students during class. Some key methods for encouraging active learning during class include incorporating their pre-class experiences, conducting discussions, encouraging student participation, and evaluating student understanding with a response system, such as i-clickers. After the class time, students need apply what they have learned in answering additional questions on homework assignments and in hands-on laboratory experiences. Lessons learned after several years’ worth of step-by-step efforts to approach these goals in an introductory acoustics class, which serves a wide range of majors as a general science elective, are presented.

Teaching and learning musical acoustics in a "music technology" program

Helping math-averse students to learn musical acoustics can be challenging. Many universities offer a degree program entitled “Music Technology.” While the details of Music Tech programs differ, the general curricular focus includes music theory, electronic and computer music, audio recording and mixing, multimedia production, and computer applications in music composition. Music Tech programs also typically require a “Science of Sound” course that is intended to introduce the physical and mathematical concepts of musical sound and the basic principles of room acoustics. But unlike traditional acoustics students with a physics or engineering background, many students in the music tech programs are unconventional learners who do not tend to have much background in mathematics and the traditional science topics that would be the customary prerequisites for a formal acoustics class. This situation provides an interesting challenge--and a great opportunity--for the instructor to help students learn about acoustics and audio topics while side-stepping the students’ disdain for mathematical formulae. This paper presents one Music Tech lesson example: teaching musical instrument acoustics using a lumped source-filter-coupling model. The learning outcomes are sufficient for the students to understand and implement useful empirical models and simulations.

Computer modeling in graduate level underwater acoustics

The more a student can become part of the teaching process, the more engaged he is. In a laboratory setting, this involves physically implementing the learned theories. However, for upper level graduate courses, laboratory experiments are often unrealistic. For example, in an underwater acoustics class, it is impossible for a student to physically realize ray bending in the ocean without a large-scale experiment. However, computer modeling can bridge the gap. In this example, students write their own simulation of underwater propagation based on concepts learned in the lecture. Through the computer simulation, students manipulate the environment to determine the effects on acoustic propagation. As the course progresses, interface and target scattering and array and signal processing are added to the propagation code, leaving the student with a comprehensive ocean acoustics modeling toolkit.

Beyond architectural schools.

The legacy of Bob Newman and Ted Schultz has benefitted architects, acousticians, and many others. This paper will summarize some of the author’s efforts to carry on their pedagogical spirit. The architectural acoustics class at Berklee College of Music began in 1987, with nearly 3500 total students over the years. A number of those students have been Newman Awardees, and some students have become teachers and even Newman Award mentors. The text “An Appreciation of Acoustics”, with funding support from the Schultz Grant, was written primarily for the Berklee class, and has been used elsewhere. The ASA College of Fellows recently began the Outreach to Undergraduate Students program, which has effectively introduced acoustics as a potential vocation to students in various schools and curricula.

Musical acoustics as a general education course.

Musical acoustics is a highly interdisciplinary field of study, drawing elements from music, physics, psychology, engineering, architecture, computer science, and electronics. As such, a course in musical acoustics for non‐science majors is an ideal option for a general education science course with laboratory at many colleges and universities. Students with a predisposition against science courses may be more willing to engage in an acoustics class if they perceive that the course will overlap with their interest in music. An overview of a typical course in musical acoustics will be presented. A summary of topics, classroom demonstrations, laboratory activities, and active learning techniques will be presented.

Far field performance of an anechoic chamber used for speech and hearing research.

The department has a 13×7×8 ft fully anechoic chamber whose commissioning records were misplaced. The graduate acoustics class measured the acoustics of the chamber from 250–2000 Hz in preparation for future research projects. The focus was on the far field and its limits (near field, and approach to wedge tips). Four groups of students made measurements along the same path. The difference in the levels at a location from that at a reference location was calculated. The mean and standard deviations of these differences were then calculated to compare these measurements with the inverse square law theory. Some measurements were also made in the near field, and closer than one-quarter wavelength from the wedge tips. The average of the means from 12–74 in. was 0.73 dB below theory. The average 95% confidence limits of these data in this range was +/− 1.1 dB. These deviations compare favorably with the acceptance criteria in the ANSI standard. The near/far field guideline also appears to be reasonable. Measurements closer than one-quarter wavelength from the wedge tips may be possible. However, further extremes characterization is needed. Envelope noise reduction should also be measured.