Benjamin M. Faber

Active minimization of acoustic energy density in enclosed sound fields

Minimization of acoustic energy density has been investigated for active noise control applications for enclosed sound fields. The standard approach of minimizing the squared acoustic pressure has been shown to often lead to localized control of the sound field, which may be undesirable. It has been shown that minimizing the energy density often leads to improved global attenuation of the field, since quantities dependent on both the pressure and particle velocity are minimized. This penalizes active control solutions in which the pressure is minimized and the particle velocity is increased, as often occurs when simply minimizing the squared pressure. Minimizing the acoustic energy density also requires multiple microphones to be integrated as part of the error sensor. However, in many cases the number of microphones can be reduced by strategically placing the sensor in a location where one component of the particle velocity is assumed to be negligible. Active control results will be shown for an enclosed...

Acoustical measurements with mobile devices and the challenge of standards compliance

With more attention being brought to the use of mobile devices for acoustical measurements, questions of measurement quality and standards compliance continue to be raised. What kinds of acoustical measurements are realistic with a mobile device? Can a smartphone or tablet be used as a properly qualified sound level meter? If not, under what conditions might it be appropriate to rely on a mobile measurement solution? For the purposes of this presentation, the IEC 61672 standard for sound level meters will be discussed with respect to mobile measurement apps and devices.

Accurate mobile noise measurements: Challenges for the app developer

The ubiquity of mobile computing devices, their connection to the cloud, and their media-centric nature makes them attractive for wide scale acquisition of acoustical information, including human noise exposure in various environments and at various times. One concern in harnessing the potential of such a network of devices is ensuring that each device is able to acquire the desired acoustical information with sufficient accuracy. It is possible to make accurate acoustical measurements, as long as care is taken to ensure that the hardware, software, and users all work together to ensure success. System software, signal acquisition hardware, microphones, the mobile devices and the people who use them each present certain issues and challenges to the process of making accurate and reliable acoustical measurements. Various of these issues and challenges will be presented and discussed from an app developer’s perspective.

Applications of mobile computing devices in acoustics

In the emerging post-PC era, more and more day-to-day computing tasks will be accomplished with mobile devices, such as the iPhone and iPad. Efforts to bring acoustical measurement and analysis tools to mobile devices have already begun. Mobile devices are not only smaller and lighter even than notebook computers, but they typically employ capacitive touchscreen technology, which enables an unprecedented level of interactivity between user and device. The media-centric nature of the current crop of mobile devices also makes them well-suited for acoustics-related applications. Several examples of hardware and software solutions for acoustical measurements with mobile devices will be presented and discussed.

Tablet tools for teaching acoustics

Recent advances in tablet computing technology have in some ways made tablet devices, such as the iPad, an attractive and viable alternative to the traditional notebook computer in and out of the classroom. Tablets are not only smaller and lighter than notebook computers, but typically employ capacitive touchscreen technology, which enables an unprecedented level of interactivity between user and device. The media-centric nature of the current crop of mobile devices also makes them potentially useful as teaching aids, both for classroom demonstration as well as for hands-on experimentation. The tablets utility is further enhanced by wireless and/or mobile Internet connectivity, as well as an increasing amount of available third party software. Potential uses of a tablet computer in teaching acoustics will be discussed.

Equalization of a one‐dimensional sound field with a movable source

An experimental plane‐wave tube with a movable side‐branch loudspeaker was used to study simultaneous source and sound field equalization. The effects of equalization and inverse filtering were evaluated for different measured field quantities. Parametric equalization filters were designed based on acoustic pressure and total energy density at a point within the tube. An adaptive filter based on total energy density and the filtered‐x algorithm was also implemented. The results of the equalization methods are compared and their advantages and disadvantages are explained.

System identification and energy‐based active noise control performance

An active noise control system, which minimizes acoustic energy density, can often become unstable due to significant changes in the acoustical environment in which it operates. Typically, the control system of interest, which is based on a modified version of the filtered‐x LMS algorithm, is operated with a fixed set of system identification filter coefficients. These coefficients are determined off‐line, prior to execution of the main control algorithm. The performance of the control system depends on the quality of the system model obtained through the system identification algorithm. Changes in the system transfer function and impulse response, due to various factors, including temperature, boundary conditions, and sensor/actuator location, have been investigated. Results will be presented, which give indications regarding what types of changes to the system have the greatest effect on the transfer function and impulse response, and how sensitive the control system is to those effects. The effects of ...