Words and photos by Rafe Arnott except where noted. Photo above: Altec 604e Super Duplex drivers in original Altec 612 utility cabinets.
There is a pull off along the road of high fidelity where specifications mean nothing, and there are no rules. This place is not referenced in audiophile-related footnotes. It is not mentioned on Internet forums. No one can tell you when you’ve arrived – there is no signpost – there is just a desire to enjoy one’s music. It is not a haunt of the too precious by half. There are no sonic room optimizers and a disorienting lack of AC or speaker cables thicker than one’s arm. There is a bohemian hedonism to the gear, the space… the culture of listening. The lack of pretence can make modernists uncomfortable. I mention this because the Altec 604e Super Duplex would be just the type of speaker heard through the car windows as one rolled onto the highway’s verge and killed the engine.
This pull off is an aspirational oasis for some, and warily eyed by those who prefer high fidelity remain a singularity. As in, keep it to yourself, without the distraction of something as hackneyed as other people. Within this closeted space music is less about sharing, or enjoyment. It’s purpose is to be used as a yardstick for repeated measure against a subjective bar of sonic reference. And while technical merit is an integral part of a design concept, be it architecture or an amplifier, it should not be the sole arbiter of greatness. Which is why, even though the 604e is a product of decades of audio engineering, it is less concerned with peerage than producing supremely musical sound.
Photo below: The 604e is quickly distinguished by its gloss white speaker frame and gloss grey magnet structures. The 604e saw the LF motor provided with a full thickness top plate and a shorter voice coil then previous iterations to produce more linearity at low frequencies. The stock Altec N-1500-A crossover network has been replaced here with a Werner Jagusch autorformer crossover wired up with a mixture of Belden and Western Electric cable. This original cabinet shows the minimal damping used from the factory.
The Super Duplex can trace its roots back to 1941. That was when the All Technical Products Company purchased the Lansing Manufacturing Company (LMCO) and the newly combined entities’s names were shortened to Altec Lansing. Not long after this corporate marriage, a Los Angeles radio broadcaster – Art Crawford – made a request for the company to develop a compact loudspeaker as the Voice of The Theatre (VOTT) models with their massive low frequency (LF) horn-loaded bass enclosures and high frequency (HF) horn assemblies were simply too large for practical home audio use. His suggestion of a coaxial design with combined HF and LF drivers was green-lighted by audio engineer George Carrington Sr., then president of Altec who, with help from Jim Lansing and John Hilliard, brought the concept to fruition.
The 604 series was considered the de facto monitor for most North American and European recording studios throughout the ‘50s, '60s into the ‘70s, including Abbey Road/EMI, Apple Records, American Sound Studio in Memphis and A&R in New York to name but a few."
-Rafe Arnott
Image left: May, 1947 Altec sales catalog featuring the "Duplex" in an early iteration. Image courtesy of Lansing Heritage.
With off-the-shelf LMCO components, the prototypes were turned out quickly. The LF driver started life as a field coil motor from a LMCO 287 compression driver. It was used to power an LMCO 15-inch LF driver with a two-inch voice coil, with the whole assembly mated to a stamped steel frame. The LMCO 801 field coil compression driver with 1.75-inch diaphragm was used without modification for high frequencies and mounted coaxially to the back of the 287 motor. An 801 horn throat ran through the center of the low frequency field coil into a miniature six-cell horn positioned in front of the LF cone. This horn had a 900Hz cut-off frequency and a 1200Hz crossover frequency. Production started in 1943 under the name "Duplex," and designated as the 601, but in under a year it went through a major overhaul to replace the field-coil magnets and their unwieldy power supplies. This new design was to become the 604, utilizing separate, and newly-tested Alnico V magnets for the LF and HF drivers, a cast aluminum frame with a 15-inch LF driver featuring a larger three-inch voice coil.
Like the 601, the original 604’s frequency response was 60Hz~16kHz, the 604B (1949-1952) bettered this with a range of 30Hz~16kHz and switched to a 1000Hz crossover. The 604C (1952~1957) was next with increased power handling (35 watts compared to 20 watts for the 601), improved response (30Hz~22kHz), a 1600Hz crossover, an improved rubberized woofer surround (similar to the 515B), and a new HF driver (similar to the 802d), and a new vaned, sectoral horn design – this was the version with the green hammertone finish and gold decal. Then came the 604D (1958-1964) with improved suspension, cone and pole piece. Around the same time Altec introduced the 605 Duplex which suffered industry pushback because of a less efficient/powerful magnet assembly and 3dB drop in sensitivity. The 605A was replaced by the 604E Super Duplex in 1964 featuring Alnico V magnets, 20Hz~22kHz response, 101dB sensitivity, 1500Hz crossover, an 2.25-inch HF aluminum diapraghm and a return to the 604 naming convention.
Image right: A cutaway engineering schematic of a 604 Duplex courtesy of Lansing Heritage.
The 604 was the monitor of choice for many North American and European recording studios in the ‘50s, '60s and ‘70s, including Abbey Road/EMI, Apple Records, American Sound Studio, and A&R to name but a few. The demand as studio monitors stemmed not only from its notorious playback accuracy and performance track record (used to record and mix albums such as Hollies (S/T), Sgt. Pepper’s Lonely Hearts Club Band, A Saucerful of Secrets, Dusty In Memphis, Suspicious Minds, etc.) but from its technical prowess. The wide bandwidth response, point source coaxial configuration, relatively compact size, high efficiency and high output (100dBSPL/1w/4ft or 115.4dB with 35w), all made the Duplex popular with engineers and musicians alike.
But, it's also true some felt the design demanded a more rigorous approach for recording success. Beatles producer and engineer Ken Scott said of the 605a installed at Abbey Road; “They were awful. I think that’s why the Beatles stuff works – because you had to work so hard to make it sound good on those speakers. If it sounded good on there, it would sound great anywhere.”
For those who have not had the opportunity of hearing coaxial transducer designs, it can be difficult to relate how linear and point source their playback is. The electrical, mechanical and magnetic independence of the HF and LF units on the 604e while strictly maintained, is seamlessly integrated into one drive housing – the dual Alnico magnetic structures alone weigh-in at 26 pounds, 13 ounces – and reduced the cabinet size considerably from its VOTT siblings. Original cabinet specifications starting with the 601 included the “Floor Cabinet” which measured 38-inches high, by 30-inches wide and 16-inches deep, a “Wall Cabinet” which was a corner fitment, and came in at 34-inches wide and 24-inches deep, and the “Utility Cabinet” which was 29.5-inches high, 25.5-inches wide, and 17.5-inches deep. Altec nomenclature specified: "It shall be of heavy wood construction and gray industrial finish. It shall be of the bass-reflex type... It shall contain 6 cubic feet and weigh at least 63 pounds. The cabinet shall be furnished with one "grilled" opening for one loudspeaker."
I ran the 604e with gear I had on hand, which was an Audio Note UK 300b Conqueror Silver stereo power amp (seven watts), and an Oliver Sayes built 45 stereo power amp (1.5 watts), both being driven by an Audio Note UK M3 Phono preamp. The M3 was paired with a ’63 Empire 398 Troubadour turntable fitted with an Audio Technica AT-155LC moving magnet cartridge. For CD duty I ran an Audio Note CD5.1x, and clean power came courtesy the Shindo Mr. T. Various Belden, Western Electric, A23, OJAS and Audio Note UK cables were used. It’s all equipment I’m familiar with, the Sayes 45 being the newest addition courtesy a dear friend who thought I needed to hear it – which I did.
Photo below: Bobby Elliott, drummer of The Hollies, with a pair of Altec 605a (serial No.8 and No.3) at Abbey Road's Studio 2 in the mid-'60s. "All the recordings and mixes that came out of Studio Two in the ‘60s, from Cliff Richard to Pink Floyd, would have been recorded and mixed using these very Altec 605a. As a result, they played a large part in what became the "Abbey Road Sound” – Studio press release.
Listening to the Altec 604e, one of the first things one notices – same as the Altec Valencia 846b and the Altec A5x VOTT (which like the 604, are highly sought after by collectors) – is the realistic scale of the presentation, and how effortless and lifelike the upper and upper-middle frequencies are portrayed. What hits one next is the speed, textural realism and impact of the lower-midrange and bass, followed by the realization that the timbral and tonal colours are of the most natural complexion. Lastly, there is a complete lack of any so-called horn “shout” (which seems to be the first thing Internet forums attribute to any horn-loaded loudspeaker’s sound, which is weird, because just about all these claims come from people who've never heard them).
The dynamic capability from the combination of the high-efficiency 15-inch, low-frequency paper driver with three-inch voice coil and 1.75-inch, high frequency alloy compression driver (with 1.75-inch edge-wound voice coil) presents music with a dumfounding authenticity. A violin or a guitar sounds and scales exactly as one would expect a real wood-bodied violin or guitar to sound. Same for trumpets, saxophones, flutes, piano, percussion, drums, etc. Add in those three speaker designs mentioned can all be easily driven to maximum SPLs with as little as two watts and one begins ruminating that perhaps speaker designs, like recording techniques, may have peaked in the ’50s and ‘60s.
Photo below: The 604e with Empire 398 and Oliver Sayes 45 tube power amplifier.
The 604e in their 612 cabinets pressurized my 14x16-foot listening space with a light touch and allowed for apartment-friendly dimensions when it came to set-up and positioning with a roughly eight-foot triangle between the speakers and myself. Holographic imaging dead centre between the speakers shifted from 18-inches in front of the drivers focal plane to 18-inches behind depending on the recording. Word of warning; ’60s and ’70s Blue Note and Prestige mono jazz LPs through the Altecs produced hot flashes, and an original ’59 mono pressing of The Country Blues Of John Lee Hooker caused mild hallucinations. Separation of instruments and vocals (whether in harmonies or multi-tracked) was among the best I’ve encountered, making it easy to understand why the design excelled as reference studio monitors.
The sound of the Altec may not be for everyone, this hobby is too fiercely divided into tribes to expect unanimous appreciation of anything hi-fi related, but for me the 604e is an end game loudspeaker. It took everything I loved about previous Altecs I've owned (the 846b Valencia, the A5x VOTT) and rolled it into one package. Paired with low-power – or even flea watt – valve amps, the 604e proved supremely realistic, transparent and in-the-room tactile. While I've found these vintage Altec speakers to be highly sensitive to amplification, it is my opinion that through SET amps they offer their most delicate, thunderous and musical performances. As with all things in high fidelity... YMMV.
Think of this like an online subscription. Your donation supports a unique space for me to smash-up music journalism, alternative culture, high fidelity reviews and give volume to those stories and voices lost in the white noise of mainstream hi-fi media. Plus, beer money.