Altec Lansing Duplex (1944)

Name: Altec Lansing Duplex
Brand: Altec Lansing

A coaxial loudspeaker system introduced in 1944, foundational to studio monitoring with a multicellular horn and Alnico V magnet.

Overview

The Altec Lansing Duplex is a coaxial loudspeaker system first introduced in 1944 with the 604 model. It features a 15" woofer and a high-frequency compression driver arranged so that sound passes through the woofer's pole piece to a multicellular horn. The design traces back to a 1941 concept by George Carrington, with James B. Lansing overseeing tooling and manufacture. The 604 became a standard studio monitor for mastering and remained a popular professional reference speaker from the 1940s through the 1980s.

Specifications

Impedance	20 ohms
Crossover (original for 604)	N-2000-A
Crossover frequency (original N-2000-A)	2,000 Hz
Crossover frequency (N-1600-A)	1,600 Hz
Crossover frequency (604B model's N-1000-A)	1,000 Hz

Design

The 1944 604 Duplex uses a permanent Alnico V magnet structure and a coaxial driver layout where the high-frequency compression driver feeds into a multicellular horn via the woofer’s pole piece. The high-frequency section features a voice coil wound with rectangular aluminum wire. The original 601 model used a field-coil design with a 12" woofer, but the 604 upgraded to a 15" woofer and permanent magnet system.

Context

The Duplex concept was invented in 1941, shortly after Altec purchased Lansing. The 601 was the first production model, but the 604 series, introduced in 1944, became the cornerstone of the Duplex line. It was sold in limited numbers to studios and high-end audio consumers and is considered a benchmark point-source loudspeaker. The 604B followed as a successor, differing in crossover frequency and horn characteristics.

Market

Original 604 Duplex units are rare, especially in original 605 enclosures or as stereo pairs. A single speaker in an original 605 enclosure sold for $3,950, while a pair achieved $14,100 in 2011. Common modifications include replacing the original N-2000-A crossover with later versions like the N-1600-A. Decals on original units are often partially worn off.