Altec 603

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 full-range coaxial driver built during the formative years of professional audio reproduction. It belongs to Altec's Duplex coaxial family, which traces its roots to the 1943 introduction of the original Duplex concept. The 603 puts high and low frequencies into a single radiating point. It combines a 15" full-range cone with a multicellular horn mounted over an aluminum dome, aiming to extend high-frequency dispersion without losing the coherence of a unified source. It's not a modern two-way with a crossover network. 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. The edge treatment differs from later models - it lacks the pleated surround seen on the Altec 604, which points 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

The 603 gets its full-range capability from a large 15" cone paired with an aluminum dustcap that doubles as a high-frequency radiator. That eliminates the need for a separate tweeter and crossover, and it preserves phase alignment across frequencies. The aluminum dustcap is acoustically active and contributes to the extended highs, 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. The horn is designed to control and widen the dispersion of high frequencies, preventing beaming and giving 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 cellular pattern is small and dense, which suggests optimization for mid-to-upper midrange clarity rather than extreme highs.

Cast Basket Construction with Early Stamped Variants

Most examples of the 603 have a cast basket, which gives the driver substantial weight and rigidity. Sources suggest early production units were assembled with 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 supports a large alnico magnet structure. It's powerful for its time, but it has a known weak spot: owners caution that dropping the driver can permanently demagnetize or crack the alnico assembly.

Historical Context

The Altec 603 emerged in the immediate postwar period, though the exact introduction year is disputed. Sources suggest 1948, the early 1950s, or even late 1945. 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. Labeling also marks production shifts. The earliest units bear a red, white, and blue label, while later versions adopted a black and gold label, a detail collectors use to date examples.

Collectibility & Value

Market data is sparse. 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. 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.