This issue of Voice Coil opens with Industry News & Developments, where Vance Dickason highlights the new Portland Tool & Die MDT-4000 turntable, now available exclusively from Listen. This is one of the most accurate turntables available, designed to easily fit into any audio test setup and it supports the LinearX LT-360 turntable command set, making it a drop-in replacement for this much-loved, but now discontinued product.
For this first issue of 2023, Voice Coil compiled a set of valuable directories, starting with an updated listing of the many leading OEM/ODM headphone and earphone driver factories, and a complementary directory of headphone parts vendors. Also included as an extension of the topic is a directory of MEMS microspeakers and other unique earphone drivers, all compiled by Mike Klasco and Nora Wong.
Next up, Voice Coil centers completely on the always-popular Test Bench characterizations. And for January 2023, Vance Dickason was able to spend time with two very innovative drivers. The first from Purifi Audio launched in the previous year, and the second a popular shallow subwoofer from SB Acoustics that deserved to be included in Test Bench.
The focus of the first Test Bench is the PTT6.5M08-NFA-01 6.5" Midrange from Purifi Audio. This is the fourth Purifi woofer to be examined in Test Bench (see Voice Coil July 2021 for the 6.5” PTT6.5X04-NFA-01; the November 2021 issue for the 4” PTT4.0X04-NFA-01 woofer; and October 2022 issue for the 5.25” PTT5.25X04-NFA-01). The 6.5” diameter PTT6.5M08-NFA-01 8Ω midrange is pretty much identical to the previously examined PTT6.5X and PTT4.0X woofers, and includes the same constant Sd surround, cone edge stiffening ring, and low magnetic hysteresis motor design.
However, the PTT6.5M08-NFA-01 is optimized to have higher efficiency (91dB at 2.83V8/1m) for use with multiple woofer three-way design configurations. The feature set for the PTT6.5M midrange includes a proprietary eight-spoke cast-aluminum frame, completely open below the spider mounting shelf for cooling, with additional cooling provided by 12 oval-shaped vents surrounding the cone neck joint beneath the dust cap, with no pole vent. The slightly curvilinear profile paper cone made with a proprietary fiber mix is reinforced with a V-shaped edge ring. Compliance is provided by the now familiar Purifi NBR surround, with a combination of alternating sections of both reverse roll and positive roll, plus some interesting undulations within the alternating sections.
The ferrite ring magnet is completed with a neodymium pole magnet sandwiched between steel sections that serves to linearize the Bl. Driving the cone assembly is a 39mm (1.54") diameter substantial four-layer voice coil wound with round aluminum wire on a nonconducting fiberglass former. This four-layer coil has alternating two-and four-layer sections on the length of the coil with varying widths of two- and four-layer sections. Two very thick copper shorting rings surround the coil within its full linear stroke to further lower the inductance and shield the iron from the AC field of the coil.
The next Test Bench article analyzes the popular SW26DBAC76-4 10" low-profile subwoofer from SB Acoustics. Much of SB Acoustics' high-end audio developments are done by former Vifa/Scan-Speak engineers Ulrik Schmidt and Frank Neilsen at Danesian Audio, and the SW26DBAC76-4 was specifically designed (and patented) for applications that require a subwoofer that will fit into very shallow-depth enclosures.
The SW26DBAC76-4 has a unique and interesting feature set that starts with an extremely shallow 79.5mm (3.13") cast-aluminum frame. Other features include a flat 10" dual aluminum cone that is very stiff and reinforced by a large two-piece dust cap, plus an inverted cone attached at the front cone/dust cap joint. The outside rim of the inverted cone is attached to the outside perimeter of the spider, and moves with the cone assembly. The inside diameter of the spider that would normally be glued to the voice coil assembly is then connected to the motor structure. This is a clever design.
Also in this issue, Vance Dickason pays tribute to his friend and audio industry legend Carl Perkins (1942 - 2022).
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