Concept Of Acoustic Impedance Research Articles

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.

An acoustic impedance probe for the teaching of musical acoustics to non-majors

Physics of Music or similar titles are found in the course catalogues of many colleges and universities. Almost always such courses are directed at non-physics majors and even non-science majors. As a result the course materials must be presented without reliance on advanced mathematical concepts, and thus a great deal of in-class demonstrations combined with video clips are used instead. For example, the concept of acoustic impedance, when introduced rigorously, requires the use of complex algebra. However, a discussion on a qualitative level can be done in a way that is accessible to undergraduate students without a great deal of math background. In order to introduce some measure of quantitative discussion, we are using a simple home-built impedance probe to record the input impedances of simple air columns as well as real instruments. In this talk we will discuss the details of the impedance transducer and show how it can be used to demonstrate how a flared bell changes the resonances of cylindrical air columns, the effect of differently shaped mouth pieces on the acoustic properties of a brass instrument, and a number of other characteristics of musical instruments.

Non-conforming finite element method for efficiently computing multilayered microperforated plate absorbers

The concept of acoustic impedance is a very useful model approach to efficiently compute configurations for sound absorption. Thereby, the measurements are performed by an impedance tube and the obtained data is used for the first order Robin (impedance) boundary condition within the numerical simulation. However, this approach is only valid for sound incidence perpendicular to the boundary. A second approach is to resolve the volume of the absorber and use a rigid or even elastic frame model. Especially for multilayered silencers based on microperforated plates (MPPs) the volume resolving approach is beneficial. Here, a main challenge is to cope with the quite different mesh sizes needed for accurately resolving the waves in the MPPs and the surrounding air regions. To efficiently simulate such designs, we apply a Nitsche-type mortaring within the Finite Element Method to allow for non-conforming meshes and thereby directly connect the different mesh sizes in the MPPs and surrounding air regions. We will discuss in detail our absorber design, the performed measurements and numerical simulations and plan to publish the complete setup and results as a benchmark case for computational acoustics.The concept of acoustic impedance is a very useful model approach to efficiently compute configurations for sound absorption. Thereby, the measurements are performed by an impedance tube and the obtained data is used for the first order Robin (impedance) boundary condition within the numerical simulation. However, this approach is only valid for sound incidence perpendicular to the boundary. A second approach is to resolve the volume of the absorber and use a rigid or even elastic frame model. Especially for multilayered silencers based on microperforated plates (MPPs) the volume resolving approach is beneficial. Here, a main challenge is to cope with the quite different mesh sizes needed for accurately resolving the waves in the MPPs and the surrounding air regions. To efficiently simulate such designs, we apply a Nitsche-type mortaring within the Finite Element Method to allow for non-conforming meshes and thereby directly connect the different mesh sizes in the MPPs and surrounding air regions. We will...