Back in the Dark Ages, loudspeaker design was commonly based on semi-enlightened experimentation, with new enclosure configurations appearing almost monthly in professional and consumer journals. One of those, published in Wireless World in October of 1965, was A.R. Bailey’s transmission line, a long, selectively resistive, folded-and-sometimes-tapered tube that loaded the back of the (woofer) driver for low-bass reinforcement. The term “transmission line” was misleading; a transmission line in a loudspeaker is designed to absorb all but the very lowest frequencies of the driver’s rear-going output, while the thing it was named for—the electrical transmission line—is designed to preserve as much of a signal as possible. Oh, well.
Shortly after the first commercial transmission line products emerged, from Radford Electronics in the UK, IMF Electronics adopted the concept and launched a commercially successful loudspeaker line. Infatuated by their products, I built several loudspeakers, both passive and active, based on IMF principles.
But the loudspeaker landscape was changing, largely as a result of two developments: the continuing rise of acoustic suspension (sealed box) designs, which had started in the 1950s, and, especially, A.N. Thiele’s codification of the parameters for loudspeakers with ports,1 which occurred at about the same time that the transmission line was introduced. Now one could design speakers that were more compact and, in many cases, more efficient, with more predictable results. So, transmission lines quickly faded in popularity. As far as I know, The Professional Monitor Company stands today as the technology’s most avid and important advocate.
Description Two-way transmission line loudspeaker. Drive-units: 0.75” (19mm) Sonomex soft-dome, ferrofluid-cooled tweeter, 2 × 5.5 (140mm) natural-fiber bass drivers with Advanced Transmission Line (ATL) loading. Crossover frequency: 1.7kHz. Cross-over slopes: 24dB/octave. Frequency range: 28Hz– 30kHz. Impedance: 8 ohms. Sensitivity: 89dB/W/m.
Dimensions 40.6 (1030mm) H × 6.1 (155mm) W × 15 (380mm) D. Net weight: 44lb (20kg).
Finishes Metallic Graphite, White Silk.
Serial numbers of units reviewed 0055/0056.
Price $12,000/pair. Approximate number of dealers: 6. Warranty: 25 years. Labor and parts.
Manufacturer The Professional Monitor Company Limited, Holme Court, Biggleswade, SG18 9ST, UK.
US distributor: Motet Distribution Inc. (a division of XLO International Inc.), 90 Nolan Court, Unit 30-32, Markham Ontario L3R 4L9, Canada. Tel: (905) 474.433. Tel: (650) 996-2295. Web: motetdistribution.com
As befits its name, most of PMC’s products are made for the studio and pro-audio markets, and their large, matte-black boxes seem strong and serious,2 especially when stacked with matching subwoofers.
PMC’s consumer products are a stark visual contrast with their professional ones, their lines svelte, sleek, and elegant. The fact.8 signature3 ($12,000/pair) is all that. According to PMC, the fact.8 signature and its larger three-way sibling, the fact.12 signature, are based on “trickle-down technology applied from the fact fenestria,” the top model in PMC’s fact line. The crossover network, which employs noninductive Mundorf MResist Supreme Resistors and high-grade British-built ClarityCap Capacitors, derives from the development of PMC’s flagship—and, indeed, the presentation and the construction of the compact fact.8 signature seem comparable.
I slipped the fact.8 signatures from their boxes to find a pair of impeccable-looking slabs, finished in PMC’s Metallic Graphite lacquer (Silk White is also an option) with decorative front grilles that attach with magnets and fit firmly and precisely. No seams, joints, or attachment hardware to be seen. Simply and cleanly beautiful.
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