Aquarius Product Line Circa 1970
Left to Right: Aquarius Models 2A, 2,1,3 and 4
Harman International, Courtesy John Edwards



A Noble Experiment  

Illustrated above, is one of the most striking product lines ever developed by JBL. The Aquarius series was groundbreaking in both technology and style. Yet with one exception, its existence would be fleeting. It arrived in the marketplace after a flurry of development activity but would disappear within two years. What follows is an insight into the risks and challenges of pushing the state-of-the-art. Unfortunately, most of the documentation on this project has been lost. However, the description of events described below is based on the best information currently available.


The Aquarius Series were all based on a common design principle - slot loaded bass enclosures combined with a widely dispersed high-frequency response. The intent was to develop a series of loudspeakers that would have few limitations in room placement and a stereo soundfield that was largely independent of listener position. The idea of a widely-dispersed, stereo soundstage had been pioneered by JBL in its revolutionary Ranger designs (i.e. the Paragon, Metregon and Minigon). However, these designs required a large, curved, dispersion panel with unique requirements in enclosure size and geometry that limited their application. There was a need for a more flexible and inexpensive approach. Concomitant with this, was a brief vogue for non directional speakers that developed in the mid sixties. Such designs had been marketed by Harman Kardon and Stewart Hegeman and were particularly acclaimed in the New York audiophile market. Finally, JBL was interested in reinvigorating sales with radically new products that would stake out new ground in form and function. All of these factors combined in the late sixties to result in the development of a new series of speakers to be known as Aquarius.

Slot Loading Illustration (click to enlarge)
and Courtesy George Augspurger

The principle of slot loaded enclosures had been pioneered by Ed May, JBL's head of Product Development. Before joining JBL in 1959, Ed had been partners with Jack Frazier in the Frazier May loudspeaker company and they had introduced this concept in the mid fifties. The illustration at left shows this design in cross-section. The bass driver was actually front firing and the loading cap and panel were the front face of the speaker (i.e. the sketch is not meant to illustrate a top firing speaker).

Ed had tried to interest JBL in this concept shortly after joining the firm. However, it was not until the fad for dispersed soundfield speakers in the mid sixties that JBL saw an application. In 1968, Ed was authorized to begin development of a prototype. The original prototype was a two-way, stacked coaxial design with the drivers firing forward into a circular shaped front panel that provided the slot loading. This design showed promise, but Marketing preferred a rear facing bass driver with a rear mounted slot panel. This would allow more flexibility in cabinet design and would arguably couple more effectively with a rear wall.


Aquarius 2 and 3 Slot Loading
and Courtesy George Augspurger

Design modifications resulted in a second prototype that would ultimately be refined into the Aquarius 2 and 2A. These would be the first products developed even though the model names are somewhat misleading. The sketch at right illustrates the rear slot loading that would be used for the Aquarius 2 and later Aquarius 3. In the Aquarius 2, a 12" 123A driver was rear mounted in the center of the enclosure. Spacers were placed radially around this driver and a flat panel was attached to the spacers to provide the slot loading. Two 5" LE5 midranges were also rear mounted near the top of the enclosure. They had their own loading plugs mounted on the diffraction panel. Since the diffraction panel limited response above 5,000hz, high frequencies were reproduced by a single LE20 tweeter that was direct radiating and mounted on the front panel.

Ed's original Aquarius 2 prototype was considered a sonic success. It provided a wide, deep soundstage since the slot loaded drivers produced a dense comb filter that maintained reasonably flat power response at almost any listening location. The front mounted LE20's would provide a degree of image localization. However, developing the prototype into a production system proved extremely difficult. The system was notoriously sensitive to minor production variances in transducer and enclosure tolerances. Such variations could change the sonic character from expansive and balanced to thin and nasal sounding. Eventually, drivers had to be hand picked and matched to extremely tight tolerances which added significantly to production costs.


Aquarius 1 Slot Loading
and Courtesy George Augspurger

Development proceeded on the Aquarius 1 at the same time as the 2 and 2A. The Aquarius 1 was modeled on the successful 4310 monitor and subsequent L100. The midrange and high frequency drivers were the same LE5 and LE 20 with the substitution of a 10" LE10 bass driver in place of the 12" 123A. The drivers were all front mounted and individual diffraction panels were designed for the bass and midrange. The design of these panels evolved empirically and resulted in elliptical shapes that are illustrated in the sketch at left. It is interesting that this design proved to be the least prone to production variations and was arguably the best sounding of the series.


Development of the Aquarius 1, 2 and 2A were virtually complete when Ed May left JBL in 1970. Refinement of the partially complete Aquarius 4 fell on the shoulders of George Augspurger, who was then Technical Director of JBL

Aquarius 4 Geometry
and Courtesy George Augspurger

The original concept for this speaker was a very compact, columnar design that top mounted an LE8T. This driver operated full range and fired into a conical diffuser that would provide 360 degree dispersion. This concept was not new and continues to find resurgence every few years. However, it proved difficult to adapt to the chosen driver.

The LE8T was not suited to slot loading. The design had to be modified so that the loading operated more as a radial horn. Further, it was discovered that the system had to be baffled above and below the mouth so that an empty top chamber was added to the enclosure. Even with this added baffling, the short horn generated a pronounced resonance at around 1000hz . This was finally mitigated by drilling out the center of the conical loading plug to create a quarter-wave stub. However, this solution introduced a new problem. The quarter-wave trap dissipated frequencies above 5000hz so that high frequency augmentation was required. This was provided by an LE20 that was rear firing and had it's own circular slot loading to make it onmidirectional.

Equally challenging was engineering the system to develop a reasonable low-frequency response. Originally, the column below the driver was designed as a simple vented enclosure. However, this space had the geometry of an organ pipe and sounded like one. Extended trial and error was required to develop a solution consisting of a stuffed chamber open to a vented space below. This provided usable low-frequency extension to 40hz.


Aquarius 3
Harman International, Courtesy John Edwards

The final speaker to be developed in the series was the Aquarius 3. This would be the sole responsibility of George Augspurger and would be the most ambitious design of them all. The desire was to develop a nondirectional speaker for the high-end market segment. It would use a large bass speaker in combination with a compression driver typical of such contemporary systems as the Olympus. However, all of the drivers would employ some form of indirect dispersion.

The starting point was a scaled-up version of Ed May's prototype for the Aquarius 2. The same configuration of bass and midrange drivers was used only the 12" bass driver was replaced with the 14" LE14A. An LE85 compression driver would be front mounted in combination with a radial horn that would be developed specifically for this system. The new horn would be designed for as broad a dispersion pattern as possible and would require pioneering research and development.

Aquarius 3 Horn Geometry
and Courtesy George Augspurger

George's experiments with horn design began inauspiciously using teakwood serving trays, around 18" in diameter, from a local home supply store. The first horn worked fairly well, but response was noticeably different on and off axis. George addressed this by cutting tapered, radial slots in the dish to generate a more diffuse sound source. This idea was prompted by Karlson's radial slot concept, popular in the 1950's. The slotted horn was much closer to a hemispherical source, with very little loss in overall efficiency.

Mounting the horn on the front panel, as Ed May had originally envisioned for the Aquarius 2, worked pretty well but there was a noticeable change in response directly on-axis. Mounting the horn on the top panel, as one would expect a radial horn to be oriented, smoothed out the coverage pattern but didn't sound as good. The best results were obtained by tilting the horn at 45 degrees, which accounts for the distinctive letterbox shape of the enclosure.

Modifying the back panel to accommodate the larger LE14A driver was relatively straightforward. However, George soon discovered that slot loading presented a unique set of issues. This loading effectively added significant mass to the cone at low frequencies. With the bass reflex vents inside the slot, there was additional mutual coupling between woofer and vents. As a result, the woofer cone had to be lighter and the suspension stiffer than a standard JBL LE14A. Even so, bass response was considerably more extended than conventional JBL systems of similar size and the diffraction panel naturally attenuated the midrange response to provide an easier match between drivers.

In the opinion of its designer, the Aquarius 3 was a very good sounding speaker that could hold its own with contemporary JBL systems. In particular, its solid and extended bass response was arguably superior to most JBL speakers. To this day, George Augspurger regrets not having purchased a pair for personal use.


The Aquarius 1, 2, 2A and 4 were introduced in 1970. Their unique styling and engineering generated significant buzz within the industry. However, this did not translate into sales. The Aquarius 2 and 2A were a particular disappointment. It quickly became apparent that their relatively high costs, both in development and production, would not be recouped. They were cancelled before the end of the year. The failure of these speakers led to the cancellation of the Aquarius 3 even before production could begin. Only four development pairs were ever produced before the program was terminated. The Aquarius 1 and 4 would soldier on into the 1971 production year. The Aquarius 1 was produced in a limited production run and was discontinued after this run sold out. Only the Aquarius 4 would continue in production for the next five years.

L120 Aquarius Q
Harman International, Courtesy Ed Lacinski

The relative success of the Aquarius 4 was interesting in light of the fact that it arguably had the most compromised performance of the series. However, in its favor were a compact form factor and timing. The extremely small footprint of the columnar design lent itself to great flexibility in placement in any number of home environments. The early seventies saw a briefly-lived technology development that accentuated this advantage. This was the introduction of quadraphonic sound. The need to accommodate four speakers for quadraphonic reproduction made the small footprint of the Aquarius 4 even more desirable. In fact, the relative success of this design led to a subsequently larger variant that was introduced in 1975. This was the three-way L120 Aquarius Q. However, by the mid seventies, the quadraphonic phenomenon was on the wane due to market segmentation caused by a lack of standards. By 1977, all of the Aquarius series would be discontinued.

Nonetheless, the legacy of the Aquarius series would continue into the 1990's. The Aquarius 4 would be redesigned and reintroduced as the S2 in the mid 1980's. The single LE20 in the original design was replaced with four 1" tweeters placed in the corners of the low-frequency slot. The LE8T was replaced with the 108H bass driver. The enclosure design and dimensions were virtually identical to the original. The S2 was introduced with a companion subwoofer called the S1. This mounted another 108H bass driver in a similarly dimensioned columnar enclosure. The last incarnation of the Aquarius concept was developed strictly for the Asian market in 1990 as the S119. This was virtually identical to the S2 but used shielded drivers and was produced in a gloss finish.


The disappointing sales of the Aquarius series were due to three primary factors. First, the design concept was arguably a technological step backwards. Rather than raising the level of sonic accuracy, it was meant to address deficiencies in the recording process that would ultimately be rectified as the industry matured. It must be remembered that this was the era of "ping pong" stereo. Rather than attempting to capture a three-dimensional soundfield, mixes were routinely engineered to just place separate instrument tracks on separate channels. On these recordings, a diffuse soundfield could artificially create a sense of space.

Second, there was insufficient time for development. This was compounded by the desire to introduce a whole family of unusual loudspeakers without allowing enough time to thoroughly engineer and test the systems. Given another six months, the sound quality of the Aquarius 2 and 4 could have been greatly improved.

Finally, there was a problem posed by the radical departure in sound compared to previous JBL products. JBL was a successful high-end manufacturer with a reputation for a distinctive sonic character. The Aquarius series was considered by many to be too much of a deviation from this character. It therefore failed to find immediate acceptance in its existing market niche. Further, the diffuse sound concept was difficult to set up in a typical listening room, and almost impossible to demonstrate effectively in a dealer's showroom. This made it difficult to appeal to a new market niche.

The lack of market acceptance was disappointing, but it was not disastrous for the company. At the time. JBL was a small, high-end company that operated without marketing studies or focus groups. A new design was sent to dealers and it either succeeded or failed. The fact that the Aquarius concept failed was unfortunate, but it was taken in stride. In fact the introduction of the Aquarius series coincided with the introduction of the L100. That speaker would go on to be the most successful speaker ever produced by any manufacturer in its day.

2001 Don McRitchie
based on information provided
by George Augspurger