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.

In Voice Coil October 2024, Claus Futtrup writes about Compliance Alteration, and Mike Klasco and Nora Wong prepared an updated directory of Integrated Electronics for Loudspeakers. James Croft returns with a "Loudspeaker" patent review, granted to industry veteran Michael Levy, and Vance Dickason focuses solely on the eagerly awaited Purifi Audio PTT10.0X04-NAB-01 10" Midbass Woofer.

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.

In this issue of Voice Coil, Vance Dickason continues his exploration of Outboard DSP systems with a review of the Marani Pro MIR4801 Audio System Processor. And Claus Futtrup explores the concept of a transitional alignment between B4 and LR4. Next, Mike Klasco writes about new materials for cabinets and enclosures. On Test Bench Vance Dickason characterizes the new B&C Speakers DE640-16 1.4" compression driver and the latest Satori MR13TX-4 5" TPCD TeXtreme midrange from SB Acoustics.

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.

In this issue, Vance Dickason kicks off a series of outboard DSP processor reviews, starting with the Danville dspNexus. Next, Claus Futtrup writes about the Critically Damped Fourth-Order (CD4) bass reflex alignment. As scheduled, Mike Klasco writes about New Materials and Technologies for Voice Coils, and there's an updated directory of 2024 Voice Coil winders, converters, lead out wire, and more. On Test Bench, Vance Dickason assesses the new B&C Speakers DH450-8 1" compression driver and the Stereo Integrity M3 3.5" carbon midrange driver.

In this July 2024 issue of Voice Coil, Vance Dickason introduces a new article series about Outboard DSP, Mike Klasco explores Diamond Coatings for Speakers, there is an updated directory of Adhesives, Coatings, Sealants, High-Tech Thin Films, Converters, and Dispensing Equipment vendors, and Claus Futtrup writes about the IB4 Bass Reflex Alignment. Vance Dickason’s Test Bench characterizes the new Scan-Speak 15W/8534T00 5.5” woofer, and D3404/606200 Metamodal TPCD tweeter.

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.

In the June 2024 issue of Voice Coil, Claus Futtrup explores the Linkwitz-Riley (LR4) Bass Reflex Alignment, in Acoustic Patents, James Croft revisits an important invention from Bang & Olufsen, which has been granted the respective patent, and Vance Dickason characterizes the new Wavecor WF211PA01 8.25" woofer and the Faital Pro 10PR330 10" woofer, both suitable for PA systems and professional applications. Finally, there's an updated industry directory of Headphone Test & Measurement Equipment.