Altec 605A Duplex

Name: Altec 605A Duplex
Brand: Altec

1959 - 1964

The 605A Duplex was Altec's attempt to evolve the 604 design with a modified magnet structure. It offered some technical improvements, but the market rejected it in favor of the classic 604 formula.

The 605A Controversy

The 605A was meant to replace the 604C with an improved magnet structure. Several factors led to its poor reception:

Reduced Sensitivity: The modified magnet assembly resulted in 3 dB less output than the 604C
Name Recognition: The "604" was an industry standard; customers wanted a 604, not a 605
Cost Reduction Perception: Some viewed the changes as cost-cutting rather than improvements

Some listeners preferred the 605A's slightly different voicing. They found it smoother in the midrange for home listening.

Technical Differences from 604

The 605A differed from the 604 series in several ways:

Shared Magnet Assembly: The LF and HF sections shared a common flux path, reducing the total magnet weight
Reduced Efficiency: The trade-off for the shared magnet was lower sensitivity
Similar Components: The cone, voice coil, and diaphragm were essentially the same as the 604C

The Green Hammertone Finish

The 605A is easy to spot by its green hammertone paint finish with a gold Altec Lansing decal. Some 604C production used the same finish.

Collectibility Today

The 605A had a limited production run, and it has become collectible. Some enthusiasts seek it out for its:

Unique history as the "rejected" Altec
Slightly more "domesticated" sound compared to the 604
Distinctive green hammertone appearance
Rarity compared to the abundant 604 variants

Paul Veneklasen's Objection

Audio historian Paul S. Veneklasen worked in Altec's acoustic research department. He later noted that he had objected to the horn design changes (from true multicellular to vaned sectoral) that occurred around this period. He believed they were cost-motivated rather than acoustically beneficial. His objections were overruled, and the vaned horn remained standard through the 604G and 605A production.

Historical Outcome

Due to customer demand, Altec reintroduced the 604 as the 604E "Super Duplex" in 1964, which ended 605A production. The 604E restored the full separate magnet assemblies and kept some of the technical improvements developed during the 605A era.