Altec 603

Name: Altec 603
Brand: Altec

A single 15" full-range coaxial driver that carries the legacy of Altec’s early Duplex engineering in cast metal and alnico magnetism

Overview

The Altec 603 isn’t a complete speaker system—it’s a statement in driver design, a full-range coaxial unit built during the formative years of professional audio reproduction. As part of Altec’s Duplex coaxial family, which traces its roots to the 1943 introduction of the original Duplex concept, the 603 represents an evolution in integrating high and low frequencies into a single radiating point. This driver combines a 15" full-range cone with a multicellular horn mounted over an aluminum dome, aiming to extend high-frequency dispersion without sacrificing the coherence of a unified source. It's not a modern two-way with a crossover network; instead, it relies on mechanical and acoustic design to cover as much of the audible spectrum as possible from one driver. Owners report it uses the same cone and phenolic spider assembly found in the Altec 515 woofer, suggesting a lineage of proven components adapted for broader response. The edge treatment differs from later models—specifically, it lacks the pleated surround seen on the Altec 604, pointing to an earlier engineering approach.

Specifications

Manufacturer	Altec
Product type	Coaxial speaker driver; fullrange driver; MultiCell Diacone coaxial speaker driver
Driver size	15" fullrange
Impedance	8 Ohm
Basket material	Cast

Key Features

15" Full-Range Coaxial Design with Aluminum Dustcap

At the heart of the 603 is its full-range capability, achieved through a large 15" cone paired with an aluminum dustcap that doubles as a high-frequency radiator. This design eliminates the need for a separate tweeter and crossover, preserving phase alignment across frequencies. The aluminum dustcap is acoustically active, contributing to extended highs—a clever solution for its era, though exact frequency limits remain undocumented.

MultiCell Diacone Horn for High-Frequency Dispersion

Mounted directly over the aluminum dome is a multicellular horn structure, a signature element of Altec’s Diacone lineage. This horn is designed to control and widen the dispersion of high frequencies, preventing beaming and ensuring more consistent coverage across a listening area. Unlike later iterations, the 603’s horn integrates mechanically with the driver’s central axis, maintaining the coaxial principle. The horn's cellular pattern is small and dense, suggesting optimization for mid-to-upper midrange clarity rather than extreme highs.

Cast Basket Construction with Early Stamped Variants

Most examples of the 603 feature a cast basket, giving the driver substantial weight and rigidity. However, sources suggest early production units were assembled using stamped steel baskets sourced from Utah, indicating a transitional phase in manufacturing. These early versions are reportedly less common, and collectors note the shift to cast baskets likely improved structural integrity and reduced resonance. The basket design supports a large alnico magnet structure, which, while powerful for its time, carries a known vulnerability: owners caution that dropping the driver can permanently demagnetize or crack the alnico assembly, a critical failure mode.

Historical Context

The Altec 603 emerged in the immediate postwar period, though exact introduction year remains disputed—sources suggest 1948, the early 1950s, or even late 1945. What is clear is that it was succeeded by the 603B in 1947, a timeline inconsistency that implies either early replacement or overlapping production. The driver belongs to the broader Duplex family introduced in 1943, a series defined by coaxial integration and professional deployment. Visual changes in labeling also mark production shifts: the earliest units bear a red, white, and blue label, while later versions adopted a black and gold label, a detail often used by collectors to date examples.

Collectibility & Value

Market data is sparse but telling. A used Altec 603B was listed for €590 on October 22, 2025, reflecting strong collector interest. Another listing on Reverb showed a used 603/603B driver with an original price of $499.99 and a "new" price of $451.24, though these figures may reflect current resale value rather than 1940s pricing. One owner reported finding a 603 inside a cabinet purchased for $8, underscoring the unpredictability of the vintage market. Despite limited documentation, the consensus among enthusiasts leans toward preservation—Steve Schell of Audio Asylum noted, “I think that 603s are a nice design, however, and well worth preserving.” The fragility of the alnico magnet remains the primary maintenance concern, with no widely available repair or remagnetization services documented.