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. This article was originally published in Voice Coil, August 2024.

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.

Voice Coil May 2024 includes valuable speaker design knowledge, courtesy of Claus Futtrup, who writes about Computation of Bass Reflex Alignments. And this issue includes an updated Microspeaker Vendor Directory, with a MEMS Microspeaker Subdirectory, compiled by Mike Klasco and Nora Wong. And Vance Dickason placed the unique W4-2315 4.5” coaxial from Tang Band Speaker, together with Faital Pro's 5HX140 5” pro sound coaxial on Test Bench.

Claus Futtrup and Jeff Candy, the two creators of the Speakerbench online tool for assisting in speaker design calculations, continue to introduce more and more tools and features in this web-based application. In order to inspire even more the loudspeaker DIY community, the two authors have created an interesting Speakerbench Youtube channel where we can find new interesting videos discussing the history of speaker design theory and specifically Loudspeaker Bass Reflex Alignments.

In the first part of this work, the authors discussed the difficulties in estimating cabinet losses using the classical Thiele-Small framework, and proposed a solution using an advanced transducer model. In this second article, the authors detail how their Speakerbench web-app offers an accurate and practical approach to this problem, and demonstrate how users will be able to easily and accurately determine the best suitable box volume for a loudspeaker system. This article was originally published in audioXpress, September 2021.

The two authors investigate leakage loss as identified with an advanced transducer model and verified with measurements. This is compared to classical Thiele-Small modeling with the intention to motivate the reader to further explore advanced parameter estimation and box simulation with the Speakerbench Speaker Design Calculations online tool. This two-part article concludes with an overview of how Speakerbench offers an accurate and practical approach to this problem. This article was originally published in audioXpress, August 2021.

audioXpress September 2021 celebrates its Speaker Builder magazine origins, once again offering an expanded focus on loudspeaker building, design, and testing. Mike Klasco provides an update on Speaker Technology, Claus Futtrup and Jeff Candy discuss Parameter Estimation and Box Simulation with Speakerbench, and Geoff Hill tells us the Tetrahedral Test Chamber Story. In this edition we pay tribute to Roger Russell (1935-2021) and we feature two great DIY projects. Now available online and in print.