Art Dudley Listening

Keith Aschenbrenner, proprietor of Auditorium 23, based in Frankfurt, Germany (footnote 1), has long been associated with the people and products of Shindo Laboratory: From the early 1990s until the EU's 2006 implementation of the RoHS 1 regulation, which banned the sale of various old-style electrolytic materials—and thus most of Shindo's products—Auditorium 23 was the brand's European distributor and, arguably, one of its most empathetic and enthusiastic retailers worldwide. Throughout that time, and continuing through to today, Aschenbrenner has also worked as a designer and manufacturer of Shindo-friendly ancillaries and loudspeakers.

Those speakers have included some popular models, such as Auditorium 23's Rondo and Solovox models, both built around full-range drivers from the French company Phy-HP. Yet Aschenbrenner—who, for years, listened at home to a pair of vintage Western Electric 555 field-coil compression drivers loaded with large, ungainly horns—has continued his efforts to design new speakers that, in his words, help the listener "rediscover the qualities of the amplifiers that Ken Shindo was making." It's worth noting that the amplifier designs of the late Ken Shindo, and those of his son Takashi Shindo, are uncompromising in that they're suited only for very efficient loudspeakers. (With few exceptions, the output sections of all Shindo amps are optimized for 16-ohm loads.)

Somewhere along the line—perhaps 10 or so years ago—Aschenbrenner hit on the idea of a speaker that could combine his preferred 555 compression driver with a modern horn of more modest size, supplemented with similarly efficient bass and treble drivers. That concept now exists as the Auditorium 23 Hommage Cinema loudspeaker ($49,995/pair without field-coil power supply), but to get there required a great deal of work and more than a little luck. "When people would ask me what I am listening to at home, I would be very open and honest. [But] it was my dream to make something like the Cinema, with a very long horn."

Hoping to find a substitute for the exceedingly rare and expensive Western Electric 555—even broken samples go for $5000 and up apiece, while functioning 555s with original diaphragms have become nearly impossible to find—Aschenbrenner turned to his and Shindo's US distributor, Jonathan Halpern, of Tone Imports. In 2010, Halpern had just signed on as the US distributor for the Chinese manufacturer Line Magnetic, which in turn announced that they would manufacture a faithful replica of the 555, to sell for $4950/pair. Although other companies have made compression drivers that were similar to the 555, and some now make 555 replicas of their own—the latter including the respected Japanese brand GIP and at least one or two others—Line Magnetic's 555 replicas would be the first to be offered commercially.

As Aschenbrenner told me, "In 2011, when Line Magnetic came on the market, we decided to try [to make a speaker that uses their 555], thinking, Well, if it's a failure, it's a failure." He then enlisted the help of physicist Uwe Meyer, his design partner on other loudspeaker projects, and set to work. They came up with a folded midrange horn that's over 43" long, yet is contained within an area just 19" deep. The Line Magnetic 555 driver is fastened to the horn's throat by means of a cast-bronze coupler shaped at an angle of 80°. This hands off to the first of three wooden horn segments, starting at a cross-section of approximately 1" and exponentially increasing in size. A 180° bend leads to the second horn segment, which leads, through another 180° bend, to the third and final segment, the mouth of which is 15" wide and 15.5" high. The horn itself is made entirely by hand, mostly of European spruce, with select hardwoods used for some parts. According to Meyer, "the ratio of heavy to light woods and the thickness of all materials had been proved to be very important" to the sound. All surfaces of the horn are given what appears to be a hand-rubbed oil finish. (When I unpacked the Cinemas, the first thing I noticed was the distinct, pleasant aroma of linseed oil.)

The result is a horn that, in combination with the 555 compression driver, has an effective range of 200Hz–7kHz. As for the Line Magnetic driver itself, Aschenbrenner praises its unit-to-unit consistency—in contrast to the original, no two of which seem to sound exactly the same—and its sound quality in absolute terms: "I have four original Western Electric 555s. Now they are on the shelf."

Compression obsession
Looking at the Hommage Cinema from the side, you could be forgiven for thinking that its 555 driver is loaded with a single-segment, unfolded horn: Most of the bronze coupler and all of the horn's first two segments are concealed within a wooden tray whose tapered sides are shaped to match the curves of the visible portion of the horn. The tray, which is covered with thin padding and fabric, gives the horn a flat bottom, to which are fastened four bronze feet, each 1.5" in diameter, with hollow centers and stiff felt washers. The feet fit neatly atop four corresponding pegs built into the top of the Cinema's bass cabinet, which measures 27.5" high by 14.75" wide by 16.5" deep. (The bass cabinet is supported by four adjustable feet—similar to but larger than the midrange horn's bronze-and-felt feet—that add about 2" to the speaker's overall height.) Much of the bass enclosure is upholstered in the same manner as the base of the midrange horn, although on portions of the front and rear surfaces, there's no wooden structure immediately behind the fabric: in these areas, the Hommage Cinema's bass cabinet appears to be an open design.

That was confirmed by Keith Aschenbrenner, who described the loading of the Cinema's two bass drivers—one 12" woofer and one 7" woofer—as being unique: "The large woofer is loaded on one side with a horn, and on the other side with a port. So it is a dipole, but with a complex [loading] structure to minimize the output—to deliberately limit, acoustically, the high-frequency output of the large woofer. The small woofer is on an open baffle, with perforations, for air movement. [Thus] we adjust the rolloff of the two drivers differently."

As for why the Cinema uses two dissimilar woofers, Aschenbrenner points to the challenges of making a full-range loudspeaker work in rooms of different size and character: "It is due to the interactivity of low frequencies and the room. These two different-size woofers are chosen because, if you have two woofers [of the same size] and there's a problem, there is double the problem. Having two different woofers minimizes the failures of similar woofers." He says that the large woofer reproduces fundamentals down to 50Hz, while the small one gives the Cinema its ability to re-create the "flavor and character" of recorded music. Uwe Meyer added that "the acoustical crossover frequencies are between 150 and 200Hz for the 12" driver and a bit more than one octave higher for the 7" driver."

Each Cinema bass enclosure contains two 50W, solid-state, class-AB amplifiers: one each for the 7" and 12" woofers. Each amp has its own input transformer, driven by the signal from the user's speaker cables (as opposed to line-out cables from the user's preamplifier), and each has its own user-adjustable level control, labeled Volume Woofer 1 (12" driver) and Volume Woofer 2 (7" driver). Next to those knobs, on the speaker's rear panel, are banana-style inputs for the system's main speaker cables, plus separate pairs of output jacks, also bananas, for directing the output of the Cinema's built-in amps to the 555 midrange driver and 597A treble driver.

The 597A is itself an interesting beast: As with the original 555, Western Electric patented the 597A in the late 1920s, and introduced it to the cinema-sound market in 1929. Also like the 555, it was a field-coil-energized compression driver with a lightweight aluminum diaphragm—yet the 597A, which is designed to reproduce frequencies up to 10kHz and beyond, is loaded by its own integral, 5"-long, exponential horn, the shape and color of which bring to mind the telephone used in all six seasons of Green Acres. (Indeed, as the sole supplier of equipment to AT&T and the developer of countless historically significant developments in the parallel fields of telecommunications and sound reinforcement, Western Electric referred to all of their earliest cinema-sound drive-units and speakers as loud-speaking telephones.)

Original samples of the Western Electric 597A are even rarer and more costly than the WE 555—at present, the going rate seems to be $10,000 and up for a single 597A. Consequently, the 597A used in the Hommage Cinema is a replica, also manufactured by Line Magnetic (and sold separately for $5950/pair). (For this accomplishment, the Chinese company appears to have been beaten to the punch, by GIP, as well as an independent designer-builder known only as Mr. Ogawa, whose work Aschenbrenner admires.) This is fastened to the upper edge of the Cinema's bass enclosure by means of a simple L-bracket, with the suggestion that the user install the speakers with their tweeters on the outer sides of the cabinets. (As originally conceived, the Cinema's 597A was mounted on a structure atop the housing of the 555 driver; this was ditched in favor of the side mounting.)

As specified by Western Electric, the original 597A and 555 drivers required 7V DC each to magnetize their field coils, used in place of permanent magnets. Like other contemporary manufacturers of field-coil loudspeakers, Auditorium 23 has noted that some degree of variance from the 7V norm is not only acceptable but, in some domestic installations, desirable. Thus the field-coil power supply included with each pair of Cinemas allows the user to adjust the voltage, in 0.1V steps, from approximately 4V to at least 8V. (It may go higher than that, but I wasn't comfortable trying.)

The Cinema's standard field-coil power supply, the NT1 ($5495), was designed by Claus Jäckle and built in Germany by his company, AcousticPlan. The NT1 measures 8" wide by 7" high by 12.5" deep and is built on an aluminum chassis, covered on top and on two sides by a distinctly cool-looking—in every sense—steel-mesh wrap. Inside are a big transformer, big capacitors, two big rheostats for adjusting voltage—each controls the voltage for one pair of output jacks, and it's up to the user whether to assign each of the two pairs to a given speaker or to let one pair do the tweeters and the other the midrange drivers—and two big selenium stacks for rectification. As with all of the AcousticPlan electronics I've seen, the NT1 is beautifully styled, with a machined aluminum front panel and machined aluminum control knobs, all finished in a matching shade of dark gray; these elements are executed so well that the NT1's entire front end looks as if molded or cast in a single piece.

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Footnote 1: Auditorium 23, Thüringer Strasse 4, D-65824 Schwalbach, Germany. Tel: (49) (0)6196-402-516-8. Web: www.auditorium23.de. US distributor: Tone Imports. Web: www.toneimports.com.