Voice Coil Focus: Quasi-Alignment Families

This article is another great contribution by Claus Futtrup, this time with direct support from Jeff Candy, the two creators of Speakerbench, the free to use web-based application for low-frequency analysis and design of loudspeakers. Another follow-up article for the Bass Reflex Alignments article series that was published in audioXpress and Voice Coil, this time, the authors discuss the important Quasi-Alignment Families where the fundamental idea is trying to approach a roll-off similar to the Butterworth B4 alignment (a maximally flat response) but compatible with real systems for which the driver Qt will not allow a true B4 alignment.

Douglas Self has been using a tried-and-true palette of op-amps in his designs. Because many new types have appeared in the last decade, he thought it was high time to evaluate those for distortion performance. In Part 1 of this article, he examines BJT-input devices using a similar protocol for five different loads and testing for basic op-amp distortion in favorable circumstances. FET input op-amps are investigated in Part 2.

Standard simulations are closely tied to the analytical framework much more than the numerical. Simulation software gives insight into physical products that could not be achieved otherwise, often leading to less attention being paid to analytical methods and descriptive mathematical expressions related to the physical application. This article explores an analytical approximation method described as a perturbation approach.

The Purifi 1ET9040BA balanced Class-D amplifier module, a Bridge-tied-load (BTL) output stage, is the second product in the company's Eigentakt range. Following a conversation with members of Purifi about the amplifier's audio performance being hard to measure even with the best available test equipment, Jan Didden, in collaboration with Rens Tellers, took up the challenge, with invaluable support from Audio Precision's parent corporation Axiometrix.

Originally launched in May of 2023, APL Virtuoso is a culmination of more than 10 years of research into binaural audio and spatial sound, offering users the ability to mix and monitor immersive audio over headphones, without the need for complex loudspeaker setups. The v2 update of APL Virtuoso introduced acoustics emulation and externalization, simulating the experience of listening to loudspeakers in a perfectly tuned room.

The market for True Wireless Stereo (TWS) earbuds has seen significant growth driven by advancements in technology and increasing consumer demand for high-quality audio experiences. Hybrid designs, which incorporate two types of drivers, are steadily entering the market as an option that allows OEMs to deliver superior sound quality. This article explores how different hybrid driver configurations enhance audio quality, user experience, and acoustic precision.

The first issue of Voice Coil for 2025 is now available and includes a new article by Claus Futtrup about computation of alignments, Dave Morrison discussing Spikes & Isolation for Speaker Decoupling and another valuable directory of Earphone and Headphone Manufacturers and parts. On his Test Bench, Vance Dickason characterizes the new Scan-Speak D3004/666000 metamodal TPCD dome tweeter and the Dayton Audio UMII10-22 Ultimax II 10" Subwoofer.

In this issue we write about some of the most innovative Drivers and Transducers from the past two years. Read about dual-driver true wireless earbuds, and how to assess listening effort inside vehicles. Douglas Self shares his latest findings on Modern Op-Amp Distortion Tests, and René Christensen explores the analytical framework that sustains great simulation techniques. Reviews of the APL Virtuoso v2 Binaural Renderer, and the Purifi 1ET9040BA amplifier module.