The Fifth Element #85

Were one in a whimsical mood, one could divide the history of hi-fi into the eras before and after Edgar Villchur (1917–2011), inventor of the sealed-box, air suspension (or acoustic suspension) bass-loading principle. It was Villchur's invention of the acoustic-suspension woofer that made possible affordable loudspeakers with deeper bass from a smaller cabinet (see Sidebar: "Sealed Boxes").

I don't know if hi-fi can claim any true Renaissance men, but Edgar Villchur is as close as anyone gets. As a student at New York's City College, he aspired to work as a theatrical set designer, and later earned a master's degree in art history. Villchur's WWII service was as a radio and radar technician. After the war, he opened a radio-repair shop in Greenwich Village and designed playback systems for private clients.

Villchur also redesigned the record player manufactured by the American Federation of the Blind, reportedly reducing the distortion component attributable to the tonearm from 12% to 4%. His awareness of the needs of blind users (books on LP preceded books on tape, CD, and download) prompted him to invent the first tonearm that damped the descent of the needle to the record's surface.

After his formal training in art, Villchur took individual courses in mathematics and general engineering as part of his self-guided education in electronics. He was essentially self-taught in audio, and necessarily so—at the time, no courses in audio engineering were given anywhere. Indeed, when New York University accepted his offer to teach such a class, it was the first-ever academic course in that discipline.

Villchur's key contributions were, first, to recognize that the single greatest impediment to improving bass extension and lowering distortion was the nonlinear performance of the mechanical woofer suspension, comprising the spider and the cone surround. Second, his solution was radically counterintuitive. Villchur's innovation used the air trapped in a sealed speaker cabinet as a more-linear "spring" substitute for the stiff mechanical suspensions of the day. The stiffness of mechanical suspensions necessitated large cabinet volumes; mechanical suspensions also operated with low distortion only within a narrow range of cone excursion. Villchur designed a loosely suspended woofer with greater excursion, and placed that woofer in a sealed box stuffed with fiberglass batting. The air inside the sealed box provided a spring-like restorative force that returned the cone to its resting position following an excursion out or in. Villchur also was apparently the first to consider the properties of the cabinet as variables to be taken into account while engineering the drive-unit itself.

It has been reported that the dimensions of the front panel of the prototype AR-1 were taken from a picture frame Villchur and his wife admired. I wish that I could tell you that that frame was of Golden Ratio (1:1.6180) proportion, but it wasn't. Based on careful measurements of a high-quality photograph of what, in the 1950s, was the earliest known surviving AR-1, serial no.0074, the speaker's front-panel proportions appear to be more like 1:1.7857. (Since that photo was put up on the AES website, an even earlier AR-1, serial no.0006, has been discovered.)

Villchur applied for a patent, and while that was pending tried to sell his acoustic-suspension idea to two established speaker makers. The first, Altec Lansing, responded that if Villchur's idea were valid, their own engineers would have already thought of it. The second, Bozak, responded that Villchur's idea could not possibly work.

In 1952, Villchur demonstrated his prototype to one of his NYU students, a young man named Henry Kloss (pronounced close to rhyme with gross). The rest is consumer-electronics history. Kloss was already building speaker cabinets in a loft in Cambridge, Massachusetts. He and Villchur pooled their financial resources, attracted other small investors, and formed a partnership called Acoustic Research Corporation. However, within two years of the AR-1's debut, Kloss and the other partners withdrew, and struck out on their own to form KLH.

Although Villchur's patent (US No.2,775,309) was granted, it was flawed in having failed to distinguish his whole-system approach—which included not only the compliance of the woofer surround, but the behavior of the air in the cabinet—from a piece of "prior art" he'd been unaware of when, for lack of funds, he'd drafted his own patent application. Electro-Voice refused to pay license fees to AR, litigated the issue, and won at trial. Though that verdict might well have been overturned on appeal, Villchur, mindful of the parallels between his situation and that of Edwin Armstrong, inventor of FM radio broadcasting, put the matter behind him. Both had obtained patents that were not as comprehensively written as they might have been, inviting protracted litigation.

Those curious about Villchur's fascinating life will find indispensable David Lander's interview with him in the January 2005 issue of Stereophile, and the page devoted to him on the website of the Audio Engineering Society (AES).

In 1957, Acoustic Research grossed nearly $1 million (more than $8 million in 2014 dollars). By 1966, AR's share of the US home hi-fi loudspeaker market was estimated to be 32% (not even Bose has ever achieved that). Furthermore, AR was selling about 1000 turntables a week. Villchur sold his interest in AR in 1967, established the Foundation for Hearing Aid Research, and was appointed a Visiting Scientist at the Massachusetts Institute of Technology.

Synchronously enough, in that same year Henry Kloss parted company with KLH. Unable to raise capital to pursue his dream of affordable projection television for the home, Kloss fell back on what he knew best. He set out to design a new loudspeaker that would sound as good as AR's legendary model 3a while costing only half as much.

The result, the Advent Loudspeaker, released in 1969, was a two-way sealed-box design that took advantage of improvements in driver-materials technology, especially for the woofer surround. In 1971, J. Gordon Holt reviewed the Advent in The Stereophile, and found that, apart from a "velvet fog" coloration that might have been transient-response smearing, there really was nothing to complain about, and much to admire, especially for the low price of $112 each. The Advent is often mentioned as the best-selling consumer loudspeaker of all time. (I have not been able to determine whether Henry Kloss actually made that claim. I suspect that it is the brand overall, and not a particular model, that might justify the boast.)

That said, even as early as 1969, the handwriting was on the wall for sealed-box designs. In 1961, Australian Broadcasting Commission researcher A.N. Thiele published, in an Australian journal, a paper that pointed the way toward a systemic understanding of the complex behavior of vented (or ported, or bass-reflex) speaker designs. Thiele's paper was republished in 1971 by the AES, followed in 1973 by Richard H. Small's treatment of the same topic, based on Thiele's earlier work. Their contributions are now usually mentioned together as the "Thiele-Small Parameters." Thiele's and Small's work made it possible to model the behavior of ported loudspeaker designs, which theretofore had been worked out by trial and error.

A ported design begins with a constellation of engineering challenges that arise from the facts that the air in the port and the air in the enclosure both act as resonant systems that also interact with each other. A poorly designed ported speaker will suffer from poor transient response at low frequencies. The resonant systems (port air and box air) lag the input signal before reaching full output, then tend to keep vibrating longer than they would in a sealed-box design. However, a well-engineered ported speaker will minimize these problems while having a more robust bass output than a sealed-box speaker of the same cabinet volume (footnote 1).

It was not only consumers who preferred smaller, ported boxes with bigger bass. Retailers and most speaker manufacturers liked them too: Shipping and storage costs were lower, as were materials costs. In the mid-1970s, the heyday of the Advent Loudspeaker, most speakers sold in the US with hi-fi aspirations or pretensions were sealed boxes. Today, very few are. Close to none, in fact, despite sealed-box designs' virtues of being less likely to excite "room boom" or "one-note bass," of presenting an easier electrical load to the amplifier, and of having a bass-rolloff characteristic that many perceive as more natural and more "musical"—or, at least, more suitable to classical music than aggressively ported designs.

The most ambitious sealed-box speaker to achieve widespread recognition was perhaps Duntech's 6' 2"-tall, 275-lb Sovereign 2001, of the early 1980s, with its two 12" woofers per speaker. Duntech 2001s are still in use in some recording studios and mastering rooms, but have not been officially imported into the US from Australia for more than 20 years, which suggests a near-total lack of demand.

So, with past as prologue, I was moved to ask ATC why their SCM7, SCM11, SCM19, and SCM40 models are still sealed boxes and not ported designs. But first, the SCM19's particulars . . .

ATC SCM19 v.2
For the history of ATC Loudspeaker Technology, Ltd., see my coverage in the February issue of the SCM19's smaller sibling, the $1499/pair SCM7 v.3. (The numerals in the names disclose the internal volume, in liters, of that model's cabinet. The SCM19's volume is 19 liters. Reportedly, the AR-1's volume was 48 liters.)

The SCM19 v.2 ($3699/pair) is a two-way, stand-mounted, sealed-box loudspeaker designed and built in the UK (footnote 2). The cabinet of the updated SCM19 incorporates the industrial-design refresh first seen in the SCM7. The prominent features of the updated look are: curved side panels; a cabinet with a lute-shaped cross-section, a fully veneered front panel with which the drive-units are mounted flush; and a magnetically attached grille of metal mesh.

The drive-units are of ATC's own design and manufacture: a new 1" SH25-76 tweeter, whose soft dome is non-hemispherical, and a 6" (150mm) mid/woofer that incorporates ATC's Super Linear (SL) magnet technology, which is claimed to significantly reduce midrange distortion. Furthermore, this driver's 3" dustcap is claimed to function like a midrange dome. The crossover frequency is 2.5kHz.



Footnote 1: All things being equal, a sealed-box design will begin rolling off in the bass from a higher frequency, but its rolloff will be half as rapid as in a ported design. The ported design will be flat to a lower frequency, but once a ported speaker begins rolling off, it drops off twice as fast. That's because the air column in the port shifts from being in phase with the woofer's output above resonance to being out of phase below resonance, and therefore switches from reinforcement to cancellation of the woofer's output.

Footnote 2: ATC Loudspeaker Technology Ltd., Gypsy Lane, Aston Down, Stroud, Gloucestershire GL6 8HR, England, UK. Tel: (44) (0)1-28-576-0561. Fax: (44) (0)1-285-760683. Web: www.atcloudspeakers.co.uk. US distributor, Consumer Products: Lone Mountain Audio, 7340 Smoke Ranch Road, Suite A, Las Vegas, NV 89128. Tel: (702) 307-2727. Fax: (702) 365-5145. Web: www.lonemountainaudio.com.

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COMMENTS
Catch22's picture

Well done my man!

remlab's picture

Very enjoyable! And after 30 years, I finally know how to pronounce "Kloss". Hah!

Mikeymort's picture

I loved this article. When I served in the Army during the middle seventies, the barracks where I lived was filled with post exchange acquired gear. Hi wattage receivers and acoustic suspension speakers. I had large Advents and a Marantz receiver. Luckily, one of my roommates had a tubed Dynaco system with A-50 speakers. (What is aperiodic anyway?) We could listen to his system hour after hour with no listening fatigue. I have a similar system today.

John Marks's picture

And so by implication does not have a primary resonant frequency.

Specifically, an "aperiodic" loudspeaker enclosure design can be looked at either as a ported enclosure that has resistance in the port, or, a sealed box that leaks.

While the Dynaco Variovent is the most familiar application, I believe that stuffing the port in the ProAc Tablette with cocktail stirrer straws accomplished the same thing.

Thanks for the kind words. It was fun to ferret out all those old stories. BTW, I asked Winslow Burhoe, who was Edgar Villchur's research assistant on the AR4, what it was like to have Villchur as a boss, and he impishly replied, "I don't know. He was never there."

A priceless moment.

JM

tmsorosk's picture

A very entertaining and informative article.

Well done Mark.

John Marks's picture

I'm John.

corrective_unconscious's picture

It's a coarses for hoarses thing.

ganyc's picture

Hi John,

Nice review. In this case do you think that "fullness" and "presence" equate to warmth? My only experience with ATC speakers was infrequent appearances at RMAF. I don't think I would have described what I heard as warm.

Thanks

Gary

hnipen's picture

Thanks for a great history lesson John :-)

Timbo in Oz's picture

system as a resonant circuit. No?

It was able to help us build good sealed boxes, too. It is possible to build boomy/heavy bass sealed speakers.

JBTWay the KEF b110 has been used in Rb boxes, in the bass-extension stand/tower for the LS3/5A. But even that didn't go particularly deep.

It is possible to get similar results to a sealed enclosure with room-gain, (still with some cone-bounce issues,) by using a critically damped QB3 alignment or even an over-damped alignment.

IME the best kind of Rb enclosure is an 'active' or 'assisted' 5th or 6th-order alignment using an active 2nd order HP filter in the line to the power amp with a little gain. Boost |\__ This almost eliminates the distortion that is visible as cone-bounce, while also limiting motor excursion, and can provide another half octave of extension.

This idea could also help with TL designs which are damned close to Rb's when modelled.

Timothy Bailey

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