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Early Acoustic Research AR1 and AR1W woofers


teknofossil
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  • teknofossil changed the title to Early Acoustic Research AR1 and AR1W woofers

Hello Tom,

Tom Tyson posted an excellent summary of the various versions of the 12 inch woofer years ago. It doesn't provide in-box measurements, but does give good information on the various changes as models progressed. I couldn't find the original post, but I had saved the text and have copied it here:

There is some confusion regarding the venerable 12-inch AR woofer used in the AR-1, AR-3, AR-3a, AR-LST, AR-10Pi, AR-11, AR-9, 9Ls, 9Lsi, AR-98Ls, AR-91, AR-98LSi, AR-78Ls, AR-58s, AR-58B, AR-58BX, AR-58BXi and possibly other AR designs through the years. This woofer in its many iterations is characterized by the flat-side or “truncated” frame, but each is very similar in performance.

All AR-built 12-inch AR woofers -- Alnico or ferrite magnet -- with the flat-edge (truncated) frame have basically the same electro-mechanical properties; i.e., all have a 2-inch voice coil, 1/2-inch overhang in the gap, approximately 1-inch long coil with 1/2-inch top plate and 9-lb. magnet structure. The ferrite magnet structure is about 1-pound heavier than the Alnico due to the shape of the ferrite magnet structure (flat and wide). All of these 12-inch AR woofers have the same free-air resonance somewhere between 14 and 18 Hz, depending on the vintage. All of these mounted AR woofers can move ½-inch in a linear fashion, and about 1-inch before bottoming (the Alnico version doesn’t really bottom, but the suspension can hit the top of the magnet). But there are other significant differences as the 12-inch woofer evolved through the years, and many of the changes through the years were subtle differences involving the compliance of the suspension system and different cone materials, etc.

The first version was the original AR-1 woofer (the prototype was based on a Western Electric 700-series woofer), a 12-inch Alnico-magnet, cast-aluminum, flat-sided-frame woofer (part #3700) with a treated-cloth, pleated surround and a straight-side cone cross section. This acoustic-suspension system was conceived 100% by Edgar Villchur (his patent), but about 75% of the mechanical driver and enclosure design was executed by the late AR co-founder Henry Kloss. This AR cone was relatively heavy (approx. 80+ gm.) with a 2-inch voice coil mounted on a bronze former or "bobbin." The AR-1 woofer is characterized by the orange-yellow cloth surround color, and no ribs or foam damping material on the center or edges of the cone. The earliest hand-made 1954 versions had the pleated surround, and also had a thicker cast frame, 1/4-inch thick rather than the 3/16-inch thick frame later adopted for mass production. The half-round surround -- shown in the original patent by Ed Villchur -- was probably the first-ever application of this now-common surround shape, was adopted after the initial-run of AR-1’s in 1954, and the pleated surround was never used after that. The half-surround simply had less distortion than the pleated surround, so Villchur decided to standardize on that design. By 1958 with the introduction of the AR-3, the company updated this woofer by adding lamp-black mixture to the butyl-rubber surround treatment to darken the surround so it would not show through the grill cloth, and added stiffening ribs to the cone cross section along with the foam damping rings. It is here that one can detect the influence of Ed Villchur and Roy Allison over the mechanical design of the system Villchur originally designed. Both were results-driven, quantitative engineers, and they realized that the woofer’s upper-end response – above 800 Hz. or so – was getting rough, so ribs were added to the cone for stiffness and foam rings were added to the center and the edge of the cone to damp resonances. It effectively eliminated the roughness for the AR-3’s 1000-Hz. crossover.

AR introduced the AR-3a in October 1967, and the same woofer that was used in the AR-3 (damping rings and ribbed cone) was used in the AR-3a until the introduction in late-1968 or early-1969 of the ferrite-magnet, stamped-frame woofer. This new-style woofer was Roy Allison’s design, and this woofer was an evolution of the original Alnico woofer with newer materials and improved damping and lower distortion. The cone was a new low-vacuum felted-paper material, with better intrinsic damping and smoother response. This woofer also had a urethane-polymer foam surround, and it was coated with a mixture of butyl-rubber for better edge damping. Most of these woofers have long-since had to have the surrounds replaced, as the urethane-foam material oxidizes after about 10-to-20 years, depending on the humidity and other factors. I actually have a NOS AR-3a woofer with the original surround intact after 34 years, but it is slowly decaying. In any event, this early ferrite AR-3a woofer was one of the best ever, with an extremely compliant suspension. This woofer had the 2-inch voice coil as in the earlier woofer, but the voice-coil former was made of Nomex, a paper-like diaelectric material capable of sustaining very high temperatures – a natural application for a woofer voice coil. The AR-3a and the AR-LST shared this outstanding woofer until the mid-1970s. Some of these woofers had round magnets, others had square magnets and others yet had round magnets with indentations in the magnet structure in three or four places. This was apparently due to different parts sources.

In 1975 AR introduced the new AR-11 and AR-10Pi as updates of the AR-3a, and these speakers also used the same basic woofer, but with improvements to the cone, inner suspension and the urethane-foam surround material. A less-porous foam material was used on the surrounds, and the edge-damping butyl-rubber coating was eventually discontinued. The inner suspension was “stiffened” somewhat to improve power-handling capability, but without sacrificing efficiency or low distortion. The original AR-3a ferrite woofer did not have the “bumped” back plate, so common to today’s modern woofers. That is, the voice coil – under extreme excursion of >1” – could travel back and strike the back plate with a frightening (and breath-taking) clatter. This usually spelled the end for that woofer. The voice coil could be flattened on the end. Unfortunately, AR never changed the back plate, and the remedy for increased power-handling capability was to increase stiffness of the suspension, especially at excursion extremes.

By the late 1970s AR made additional improvements to the same woofer, and by this time it was being used in the AR-9, and the subsequent tower and bookshelf speakers. Changes included improvements to the surround and cone material, but these changes were very subtle. The suspension was stiffer than the earliest AR-3a, but was designed such that that stiffness did not restrict the woofer’s linear excursion within its ½-inch linear range.

Finally, AR had service-replacement versions of this woofer, interchangeable in all the above-mentioned AR speakers, and these woofers had the following part numbers: 200003-0, 1200003-0, 1210003-0. There might have been other numbers as well, but these woofers were essentially the same. Later, AR began using (through AB Tech Services) the Tonengen woofer, part No. 1210003-2A (also referred to as 12100032), which was the newest and current version of the flat-side 12-inch woofer. This woofer has a slightly higher resonance of about 20 Hz., and is significantly stiffer, but is far more rugged than previous AR woofers. It sounds pretty much the same as the other woofers, but I would think it has higher distortion. It can handle much more power.

--Tom Tyson

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