Electro-Voice SENTRY 100A
An eight-inch two-way that became the default nearfield in studios that couldn't afford to guess.
Overview
The SENTRY 100A is a compact two-way studio monitor built around an 8-inch woofer. The spec sheet reads like it was written by someone who had mixed on small speakers before. Flat 45 Hz to 18 kHz response. True rack-mountability. High efficiency. And power handling that E-V's own literature calls "incredible" - a word the company apparently felt fine putting in print. The 100A turns up in equipment lists from the mid-1980s alongside Fostex recorders and Hafler amplifiers. It was the monitor you bought when the room was small, the budget was real, and the mix still had to translate.
The design brief, per Electro-Voice's own promotional material, was "human engineering" with the broadcast and recording studio engineer in mind. That's marketing language, but the feature set backs it up. A Super-Dome tweeter rated to handle 25 watts of input sits above the 8-inch woofer. That rating means the crossover isn't the weak link when someone pushes the monitor hard. E-V's literature pairs "high efficiency" with "extended low frequency" as the design goals, and the published 45 Hz bottom end is low for a box this size.
Going by the surviving documentation, the 100A is not a large-format main monitor. It's a nearfield. The compact cabinet and rack-mount option say it was meant to sit close, on a meter bridge or in a rack. E-V's own copy emphasizes "excellent imaging" alongside the flat response. The two claims go together, because a small monitor with controlled dispersion gives a stable phantom center at close range.
The SENTRY Family and the 100EL
The 100A had company. Electro-Voice built it as part of a SENTRY family of studio monitors, and the family grew. By 1984 the company was announcing a fourth member, the SENTRY 100EL, which took the 100A's speaker system and added a 50-watt power amplifier on the back. Recording-Engineer (April 1984, p.57) carried the announcement, describing the 100EL as combining "the superb audio reproduction" of the 100A with the integral amplifier.
E-V's advertising named the studio problems the 100EL was meant to solve: limited rack space, equipment transport on remotes, cramped video editing booths. A powered monitor handles all three. It means fewer cables, fewer connectors, no separate amplifier channel, and no power loss from a long speaker run. Mix (October 1985, p.171) ran the pitch in full, noting that the on-board amplifier made the 100EL "ideal for single-channel monitoring" and that the on-board amplifier reduces potential interconnect problems.
The 100EL's amplifier had balanced and unbalanced line-level inputs and an infrasonic filter to reduce distortion. The 100A has none of that. It's a passive box and needs an external amplifier. The Fostex/Hafler package deals that circulated in the mid-1980s paired a pair of 100As with a Hafler DH-220A, which shows what kind of amplifier the monitor expected: modest power, clean, nothing exotic.
The family also included the SENTRY 500, a 12-inch two-way with Constant Directivity, designed to widen the sweet spot so more than one person could hear the same accurate sound without beamy high frequencies. E-V rated it at 96 dB at one meter with a single watt, with 100 watts continuous and 400 watts on peaks. The 500 is bigger, louder and meant for wider coverage. The 100A is the small one, for tight spaces.
Reception and the Rack
Period coverage of the 100A itself is thinner than the coverage of the system it belonged to. Studio Sound ran the same promotional feature on the 100A in multiple 1984 issues - April (p.141), June (p.54), and September (p.65). Each time it led with the "human engineering" line and the broadcast/recording engineer framing, and each time it highlighted the Super-Dome tweeter's 25-watt input rating under the heading "Exceptional Power Handling." E-V bought that space repeatedly, which suggests the monitor was a push product. The company led with power handling and efficiency rather than exotic materials or a flat-response claim alone.
The most concrete evidence of the 100A's place in the market isn't a review. It's a dealer package. A 1980s system ad listed two Electro-Voice Sentry 100A monitors as a line item alongside a Fostex A-2 two-track, a Fostex A-8 eight-track, a Fostex 350MB console, a Fostex 3180 stereo reverb, a Hafler DH-220A power amplifier, a 360 Systems digital keyboard, a Linn Drum, and an Alpha Syntauri digital synthesizer system. The 100A was the monitoring end of a complete project studio, sold as a package.
Living With One
The 100A's practical appeal is the same today as it was in 1984. It's a small, efficient, rack-mountable two-way that goes lower than its size suggests and doesn't need a monster amplifier to get loud. The 45 Hz - 18 kHz response is flat by the standards of its class, and the imaging claim holds up in a nearfield setup where the cabinet is aimed properly and the listener is close.
Buying a forty-year-old monitor comes with the usual list. Inspect the Super-Dome tweeter first. It's the component E-V singled out for power handling, and it's also the one most likely to have been stressed. Foam surrounds, if the woofer uses them, are a wear item on any speaker of this age. The cabinet is compact and rack-mountable, which helps installation but means the box has probably been moved and racked and moved again. Check the corners and the mounting hardware.
The 100EL is the variant that gets the attention now, because a self-powered monitor is convenient in a way a passive one isn't, and because the 50-watt amplifier and infrasonic filter make it a complete system. But the 100A is the reason the 100EL exists, and it's the one that shows up in the equipment lists. If a pair turns up at a reasonable price with intact tweeters, they're worth a listen.
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