Altec Lansing Duplex

DUPLEX was the trade name given by Altec Lansing to its line of coaxial loudspeakers, beginning with the first model 601 in 1943.

Shortly after that, Altec was approached by one of its dealers, named Art Crawford, with a request to develop a compact loudspeaker.

An LMCO 801 field coil compression driver with a 1.75-inch diaphragm was used as-is for HF reproduction and mounted coaxially to the back of the 287 motor.

There has been much confusion about the original 601 due to the fact that very few were made, with almost no survivors, and because the model name was re-used in the 1950s for a completely different Altec Lansing Duplex driver.

This confusion was exacerbated in 1988 when Altec Lansing misidentified the later 12" 601 as the original 601 in their own promotional literature celebrating their 50th anniversary.

This allowed the sound to leave the horn and be dispersed largely without coming into contact with the cone of the bass driver.

The backside of the horn, which faced the LF cone, was also coated with a damping compound to reduce high frequency reflections off of it.

Both the 601 and the first 604 had a frequency response of 60 Hz to 16 kHz with a power rating of only 25 watts, relatively low but acceptable due to the speakers' efficiency.

The next speaker in the 604 line to be released was the 604B, with a slightly higher power handling at 30 watts and a better frequency response ranging from 30 Hz to 16 kHz.

Again, the power handling capacity and frequency response were increased to 35 watts and 30 Hz to 22 kHz, respectively.

His protestations went unheeded and the sectoral horn with the "fins", or as some called them, "vanes", remained in use in the 604, starting with the "C" version and continuing through the "G".

However, debate continues to this day as to the sonic superiority of Alnico V vs ferrite magnetic motors as it relates to freedom from distortion.

It also used Altec's new TANGERINE radial phasing plug, which greatly improved the HF performance.

Its compact size, wide bandwidth, high output and point source topology made it an ideal choice for the needs of the new tape recording technology introduced in the late '40s and early '50s.

There was the continuing need to critically listen to recordings long after the performance was captured to accommodate the substantial post processing now required to develop a final master tape.

However, later that same decade, it would have a resurgence that lasted well into the 1980s when UREI introduced their 813 studio monitor that incorporated a modified 604 driver with a time-aligned cross-over.

The 604-8H featured the horn used on the UREI version of the 604 in the '70s, minus the blue foam, which, after testing, was found unnecessary.