For Voice Coil August 2024, as promised, Vance Dickason has initiated a series of reviews of outboard DSP processors available in the market, all of which should be of interest to loudspeaker engineers. The series starts this month with the Danville Signal dspNexus, which is an extremely versatile and powerful DSP audio processor and DAC, crossover, and control center for any audio system. The dspNexus comes with balanced inputs and outputs, USB, S/PDIF and Bluetooth aptX HD, and processing is handled by a latest-generation Analog Devices SHARC DSP, with Audio Weaver as the programming interface. Apart from defining active crossovers, the dspNexus can handle sample rate conversation and jitter attenuation, room correction and bass management, IIR and FIR filtering, time alignment, and more. The DAC is based on state-of-the-art "Velvet Sound" DACs from AKM and there's even an headphone amplifier output and a 48V phantom-powered microphone input and a measurement ADC built into the dspNexus.If this sounds interesting, this issue of Voice Coil provides the complete characterization of its behavior, which will be expanded in the following months with other outboard DSP processors from miniDSP, Marani Pro Audio, ALLDSP, and more. All these product reviews feature various measurements made with the APx555 B Series analyzer, courtesy of Audio Precision.
The next article this month is the fourth from Claus Futtrup in his series about the invention, concept, and historical perspective of loudspeaker bass reflex alignments. The focus this month is the Critically Damped Fourth-Order (CD4) bass reflex alignment, which remains the least known and hasn't been discussed in literature related to loudspeaker design, even though it allows for interesting output properties.
As scheduled for this issue, Mike Klasco (Menlo Scientific) writes a focus article on "New Materials and Technologies for Voice Coils." A great piece of knowledge that is the result of decades of walking factory floors all over the world and unique information about how this critical part of loudspeaker technology has evolved. As Klasco notes in his introduction, "Winding some wire into a coil should be simple enough and after a century of loudspeaker manufacturing, there shouldn’t be any new surprises. But voice coil materials, process control, and topology continue to evolve and here we discuss half a dozen noteworthy new tricks." A great read.
Also as scheduled, this issue contains an updated directory of 2024 Voice Coil Winders compiled by Nora Wong (Menlo Scientific). An essential resource to identify new and existing suppliers of wire, bobbins and voice coil materials, winding machines, and winding services in the US, Asia, and Europe. Not forgetting a select list of converters, lead out wire, and magnetic fluid suppliers.
For this August 2024 issue, Vance Dickason places the new DH450-8 1" neodymium motor compression driver from B&C Speakers on Test Bench. This ultra-compact high-frequency transducer is measured along with the B&C Speakers ME10v2 90x60 hyperbolic cosine flare horn, made from injection-molded ABS. The DH450-8 is the third 1" neodymium motor compression driver to be added to B&C Speakers’ extensive range and incorporates a 1.7" high temperature Polymer diaphragm driven by a 44mm voice coil wound with aluminum wire on a high Qm non-conducting Kapton former. Of course, the fascinating feature in the DH450-8 is the patent-pending phase plug with a deliberately twisted internal channel, which is intended to improve the overall frequency response. With a 1kHz recommended crossover frequency extending to 18kHz, this compact compression driver is well suited for small stage monitors and compact PA speakers, including the new generation of lighter, more compact line array loudspeakers.
The second driver discussed in Test Bench this month is another interesting transducer from Stereo Integrity, a new company founded in 2001, targeting the home and automotive audio markets. Stereo Integrity already offers subwoofer models from 12" to 24", including an 11" shallow mount subwoofer, and Test Bench already characterized its M25 1" dome tweeter (July 2023 issue), and the TM65 MK IV 6.5" woofer (March 2024 issue). This time Vance Dickason had the chance to evaluate the Stereo Integrity M3 3.5" carbon fiber midrange driver with neodymium motor. The total depth of this driver with the proprietary cast-aluminum frame and motor structure is only 52mm (2").
The M3 includes a black woven carbon fiber/paper sandwich curvilinear cone and 1.1 convex black woven carbon fiber dust cap, with suspension provided by a synthetic copolymer surround plus a flat 55mm diameter cloth spider. All is connected at the neck joint to a 1" voice coil with an aluminum former wound with round copper wire. The FEA and Klippel designed motor structure incorporates a neodymium slug with a metal return cup (a lot of the development of this driver was done by Warkwyn). Sold in pairs, applications for the M3 includes automotive systems, home audio speakers, or studio monitors.
And this issue closes with the usual dose of Industry Watch notes, including the latest updates on the Audio & Loudspeaker Technology International (ALTI) association and its ALTI Audio Summit March 2025 event preparations.
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