Altec 9846B Biamplifier Studio Monitor Speaker System
A biamplified monitor with a 500 Hz crossover and 112 dB of headroom — the kind of speaker that makes you rethink what "loud" means.
Overview
The 9846B is one of those Altec monitors that never got the cult following of the Voice of the Theatre line, but ask anyone who's actually run a pair in a control room and you'll get a knowing nod. It's a biamplified studio monitor speaker system — Altec's own Model 771B biamplifier is built into the package, with a 500 Hz crossover at 12 dB per octave splitting the signal between a low-frequency section rated at 60 watts continuous sine wave power and a high-frequency section rated at 30 watts.
What makes the 9846B interesting is the headroom. Altec rated it for a maximum acoustical output of 112 dB SPL at four feet, equalized for flat response with pink noise, from 40 to 15,000 Hz in a free field. That's a genuinely loud monitor with real low-frequency extension for its era — 40 Hz from a studio monitor was not a given. The dispersion figures tell you it was meant to be aimed, not scattered: 40 degrees vertical by 90 degrees horizontal, a pattern that keeps the sweet spot honest in a near-to-mid-field setup.
The biamplifier's input flexibility is worth noting for anyone planning to actually use one. The 771B accepts either a 0.5 VRMS signal into a 60 kOhm unbalanced input or a 0.1 VRMS signal into a 600 ohm balanced input, both for full output — so it'll play nice with both consumer-level and professional balanced sources without an outboard line amp. Noise is specified at 80 dB below rated output on both sections, which is respectable for the period and means the amps aren't the weak link in a quiet room.
Recording-Engineer (June 1973, p.4) published the full spec sheet for the 9846B, including the anechoic on-axis response measurement at four feet — the same 112 dB maximum output, 40 Hz to 15,000 Hz window, and the 771B biamp details that appear in the DB Magazine listing the year before. That the same numbers show up across multiple period sources is a good sign Altec wasn't fudging the data.
These were sold in the UK through Theatre Projects, Altec's sole UK agent at the time, and the 9846B appears in their magazine advertising through the mid-1970s as the "Biamplifier Studio Monitor Speaker System" — the professional-grade option in a range that also included the more familiar home and theater models. That distribution channel matters for collectors: UK-market examples may carry Theatre Projects paperwork rather than Altec's own, and the 9846B was clearly positioned as pro studio gear, not hi-fi furniture.
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