Altec 21C (ca. 1958)
The Altec 21C is a large, rare horn-loaded loudspeaker system that appeared around 1958 as Altec's entry into the higher end of the home hi-fi market. It sat between the 601 and 604 Duplex in price and performance. It was a dedicated multi-way design, not a coaxial. The cabinet is a folded-horn plywood enclosure, 51 inches tall, 27 inches wide, and 15 inches deep, weighing somewhere in the neighborhood of 75 to 80 pounds. It uses a 15-inch woofer (416A or 416-8B) and an 802D compression driver mounted to a 32B horn for the high frequencies. An N800-F network crosses them over at 800 Hz.
Period references to the 21C are thin. An Audio (December 1954, p.32) article on microphone measurement technique mentions a "free field response of the Altec 21C microphone." That is likely a different product sharing the model number, or a measurement tool unrelated to this home speaker. Beyond that, the written record is largely absent from the magazines of the era.
What survives comes from collector accounts. The 21C was part of the wave of hi-fi speakers that began in the late 1950s. Owners describe its sound as detailed and warm, with a big, enveloping stage. It is very efficient and works well with low-power tube amplifiers. The downsides are plain enough. It lacks deep bass, it can sound boomy in some rooms, and the upper midrange can turn aggressive. The original high-frequency level controls are prone to corrosion, the crossover capacitors benefit from replacement, and the large cabinet can resonate, so some owners add bracing or damping.
The 21C is genuinely rare. Listings appear infrequently, and prices tend to fall in the $1,000-$1,100 range. For anyone restoring a pair, the 416-series woofer uses a cloth surround (not foam), so there is no rot issue there.
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