The CD4 Bass Reflex Alignment

In the fourth article from Claus Futtrup in his series about the invention, concept, and historical perspective of loudspeaker bass reflex alignments, he explores the Critically Damped Fourth-Order (CD4) bass reflex alignment. This alignment remains one of the least known and hasn't been discussed in literature related to loudspeaker design, even though it allows for interesting output properties.

Before computers were broadly available for loudspeaker bass reflex box simulations, engineers relied on "Alignments" for their designs. Such box alignments are typically named after equivalent filter functions that the high-pass response of the box was aligned after — for example, Butterworth (B4) and Bessel (BL4) — to name a few. This article, the third in this series, explores the rarely talked about Inter-Order Butterworth (IB4) alignment, mentioned originally by Richard Small and Neville Thiele.

Before computers were broadly available for loudspeaker bass reflex box simulations, engineers relied on "Alignments" for their designs - typically named after equivalent filter functions that the high-pass response of the box was aligned after — for example, Butterworth (B4) and Bessel (BL4) — to name a few. In this article, Claus Futtrup now focuses on the Linkwitz-Riley (LR4) Bass Reflex Alignment.

The first in a series of great value for speaker designers, this article provides an updated approach for the mathematical presentation of the various alignments, applicable to all computerized development tools. This is effectively an explanation of the code available in the Alignment Chart of the Speakerbench web application that Class Futtrup developed in collaboration with Jeff Candy.

The use of standard filter alignments represents a foundational concept in the loudspeaker industry, with an impact nearly as significant as the invention of the electro-dynamic loudspeaker principle itself. As one of the creators of Speakerbench, a web-based speaker design tool, in collaboration with Jeff Candy, Claus Futtrup is in a unique position to discuss the evolution of enclosure designs based on this electrical filter theory, including the concept of an alignment chart.

Many audioXpress readers will be familiar with Peter Dieleman from his books on the theory and practice of tube amplifiers. In this article he debunks some of the myths, such as load (mis) match in output stages, which is by definition perceived as a bad thing, when that might not be necessarily the case. Another myth example regards the efficiency of a triode output stage versus a pentode.

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.

The topology and the distribution of the wiring, partitioning between low power and high power circuits, grounding scheme, types of cables, protection techniques, and safety are important factors that must be considered to minimize the interference effects in audio amplifiers. This "tips and tricks" audio electronics article provides several details about inductive coupling effects in audio amplifiers and the simple way to minimize them.

Our readers that follow Richard Honeycutt's column Sound Control know how this series of articles covers the most fundamental topics in acoustics and electroacoustics. Most people who have been around acoustics or acousticians have heard of the Helmholtz resonator. In this article, Honeycutt discusses the extraordinary scientist for whom this device is named - Hermann Ludwig Ferdinand von Helmholtz (1821–1894) - and examines how the resonator works, as well as its uses. This article was originally published in audioXpress, January 2017.

There seems to be a lack of consideration and understanding of the acoustical characteristics of the loudspeaker’s many glue joints. In this article for Voice Coil, Mike Klasco and Steve Tatarunis detail how the influence and use of glue joints and diaphragm treatments can be used as a design tool. The report also details some significant new material options and design and measurement tools available. This article was originally published in Voice Coil, July 2017.