Simulation Techniques: Double Bass Arrays

Although the sound field in a room at low frequencies is one of the most discussed topics, approaches to dealing with room modes are typically treated as an optimization problem, and not correctly defined. This article explores a different strategy: the so-called Double Bass Array layout, using several subwoofers placed in a pattern, on the front and rear walls. Using advanced simulation techniques in order to understand what truly happens in the resulting room mode behavior, sound pressure levels, and resonances, this article builds upon existing research (Geddes, Welti, Devantier, et al.)

As computational demands can be very high when doing simulations involving coupled physics - such as is often the case for vibroacoustical transducers - this article looks at how to reduce the computational demands and associated cost utilizing symmetry schemes and dimensional reductions techniques, and the potential associated issues. This article was originally published in audioXpress, June 2024.

Having detailed how formal optimization can be used for product design of audio products such as speakerphones and waveguides, in this article René Christensen explores free-form and alternative optimization techniques where the topology of the geometry is given from the outset. Using practical examples, this article addresses shape optimization techniques, identifying useful types of boundaries and challenges to look out for audio product designs. This article was originally published in audioXpress, February 2024.

Room Gain is a term not used in acoustics textbooks as such. Room acoustics is naturally often discussed in the hifi community, since the room you put your loudspeakers in will heavily influence the sound that reaches your ears, both at low and high frequencies. In these discussions the term "room gain" sometimes comes up. This article was inspired by Erik Wiederholtz (CTO of Perlisten Audio) and his interest in the topic, and he was kind enough to provide measurements and photos from his own listening room for a sealed subwoofer as well as for a vented subwoofer.

Acoustic topology optimization is one of the most interesting new technologies in vibroacoustics. These powerful tools enable engineers to find optimal solutions to problems related to their specific applications and this article presents multiple examples in different areas. The article, originally published in audioXpress, April 2023, includes several examples of transducer geometries modified via acoustic topology optimization.

An exploration of the possibilities for product development focusing on modeling of transducers. As many engineering tasks require a common ground from which discussions among those involved in a project can take place in a structured manner, this often involves a so-called model of the concept or product. This article discusses one such model: the lumped element model. This article was originally published in audioXpress, March 2023.

This article by René Christensen (BSEE, MSc, PhD), offers a valuable tutorial that discusses the unique possibilities of three-dimensional analysis of loudspeaker driver displacement, using Phase Decomposition and Axial-Symmetrical Decomposition techniques. The article demonstrates how a total displacement on a cone surface can be decomposed into different components directly in COMSOL Multiphysics, and how this can reveal some of the underlying mechanisms of the driver.

The SonicEdge transducer - a cutting-edge microspeaker based on a unique MEMS technology that generates sound using active ultrasound modulation - introduces a completely new class of devices that can deliver constant volume velocity across audio frequencies and beyond. The article details how to model the transducer in lumped-element and finite-element acoustic simulations and how to tailor a desired SPL response using acoustic features. As originally published in audioXpress, August 2023.

In this fascinating article about common sound theory misconceptions that exist in the audio and hifi communities, René Christensen debunks three of them. Starting with group delay and phase delay, what actually happens when a loudspeaker driver moves outward and inward, and the effects of polarity and phase flip. True reference material with detailed mathematical expressions and numerical analysis. This article was originally published in audioXpress, June 2023.