In this issue of Voice Coil, loudspeaker expert Claus Futtrup continues to explore loudspeaker design options, this month focusing on the Linkwitz-Riley (LR4) Bass Reflex Alignment. 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 new article is a follow-up to the "Loudspeaker Bass Reflex Alignments” article about the concept, the invention, and a historical perspective of loudspeaker bass reflex alignments, published in the January 2024 issue audioXpress, as well as the article “Computation of Bass Reflex Alignments,” published in Voice Coil May 2024.Next up, Mike Klasco and Nora Wong (Menlo Scientific) have compiled another updated industry directory, this month focusing on Headphone Test & Measurement Equipment. In this listing for 2024, we get a broad overview of the vendors and companies providing the essential tools for measuring those specific types of transducers, from the smallest size for earbuds, to the larger dynamic and planar magnetic and ribbon drivers. From Audio Precision to Zumi Systems, find a complete overview of the latest specific measurement systems.
In Acoustic Patents, James Croft revisits an important invention from Bang & Olufsen, originally reviewed in December 2019, and which has since been granted patent US11,943,578, with newly revised claims. The patent is titled "Loudspeaker Enclosure with Closeable Port," and the inventor is Jakob Dyreby (Struer, Denmark), part of the team that recently brought us the outstanding Beolab 8. The patent describes what is essentially a hybrid acoustic suspension system, which in its most basic form is switchable between a "closed" acoustic suspension system, and a "ported" bass reflex system, based on signal level and/or volume control setting. The concept evolved from there, to use real-time adaptive sensing. A fascinating exploration of an intriguing concept.
For this month's Test Bench, Vance Dickason focused on professional audio and specifically woofers for sound reinforcement applications. The first driver to be characterized is the Wavecor WF211PA01, a new 8.25" woofer, which is only the second pro audio design from the company, renowned for its high-end home hi-fi drivers. The company decided to expand its catalog with new OEM pro audio woofers, and the WF211PA01 is basically a smaller version of the WF259PA01 10" woofer explicated in the February 2024 issue of Voice Coil. The WF211PA01 is designed much like Wavecor's high-performance home audio woofers, with a generous feature set a cast-aluminum frame, a very stiff flat black coated curvilinear paper cone, further stiffened by a 3" convex dust cap. Suspension is provided by a low-loss (high Qm) three-roll cloth surround plus a flat Conex spider. All this is driven by a 2.5" voice coil
wound on a vented black fiber glass former. The motor structure powering the cone assembly utilizes a single ferrite magnet.
As part of Wavecor’s Balanced Drive motor format, the WF211PA01 further incorporates an aluminum shorting ring that reduces distortion caused by eddy currents as well as a shaped, extended pole piece. Continuous rated power handling (IEC-268-5 with no additional filtering) is 170W (300W short term). Intended applications include both PA systems and studio monitors, or any place where high sensitivity and high-power handling transducers are required.
The second driver on the Test Bench for this issue of Voice Coil is the Faital Pro 10PR330 10" woofer. In this characterization, Vance Dickason revisits a bit of the origins of this Italian company founded in Milan in 1958. The company's new high-power handling 10" woofer is intended for line arrays and large PA systems, or as a midbass driver in multiway systems — apparently it has also been also used successfully in bass guitar applications.
The feature set for the 10PR330 starts with a proprietary six-spoke cast-aluminum frame with a series of cooling vents that allow air to move past the voice coil and across the milled polished and shaped front plate. Additional cooling is provided in a tapered and flared (on both ends) pole vent. The cone assembly for the Faital Pro 10PR330 woofer consists of a curvilinear paper cone along with a very stiff coated dust cap. Compliance is supplied by a coated polycotton cloth M-roll type surround and from a cloth-type flat spider. Details of the 10PR330 motor design include a ferrite ring magnet and a 2.56" diameter voice coil wound with round aluminum wire on a non-conducting glass fiber former. AES-rated power handling is 300W (600W maximum power handling).
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