Electro-Voice 100EL

Electro-Voice took the Sentry 100A studio monitor, bolted a 50-watt amplifier to its back panel, and made a monitor you could carry to a remote and plug straight into a mixing console.

Overview

The Sentry 100EL is not a new speaker. It is a Sentry 100A - the compact 8-inch two-way that had already become a fixture in studios - with one big addition: a self-contained, 50-watt power amplifier mounted inside the cabinet. Electro-Voice's own literature frames the whole thing as a logistics fix. Engineers were tired of hauling separate amplifiers to remote sessions, losing rack space to outboard power, and running long speaker cables that ate output through resistance. The on-board amplifier takes care of all three.

The amplifier is rated at 50 watts continuous sine wave into a 6-ohm load, with total harmonic distortion of 0.05% typical at 1,000 Hz. Power bandwidth runs from 30 Hz to 20,000 Hz, and frequency response is flat within half a decibel from 40 Hz to 20,000 Hz. Those are not spectacular numbers by modern standards, and they were never meant to be. The point was matching. The amplifier is mated to the speaker system, and with no cable between them, electrical damping stays optimal. There is no power loss from cable resistance, and no chance of damage from an inadvertent signal overload, because the amplifier's maximum output is chosen to work within the speaker's limits.

The input section is flexible. A balanced XLR connector handles line-level sources at a maximum sensitivity of 0.775 volts for full output, with an input impedance of 30 kilohms and a maximum input level of 8.0 volts. An unbalanced 1/4-inch phone jack offers 0.39-volt sensitivity into 10 kilohms, with a maximum input level of 30 volts. Both inputs are protected against voltage peaks up to 100 volts, but Electro-Voice's manual is explicit: do not connect either input to a power amplifier. The manual warns that doing so is redundant and will invariably increase noise and distortion. Because the inputs are bridging, up to sixteen 100EL systems can be paralleled across an unbalanced 600-ohm line, or fifty systems across a balanced 600-ohm line. That tells you Electro-Voice expected multi-monitor installations.

The speaker section carries over the Sentry 100A's core design. The low-frequency driver is an 8-inch direct radiator in an optimally vented enclosure with fourth-order Butterworth tuning. The high-frequency unit is a Super-Dome tweeter with response out to 18,000 Hz and uniform dispersion of 120 degrees at 5,000 Hz. The crossover is a 12 dB per octave dual-section type crossing at 2,000 Hz. A continuously variable, shelving-type high-frequency control on the front panel adjusts from +2 dB to -4 dB relative to flat, so the user can tailor the monitor to the room. Rated frequency response is 45 Hz to 18,000 Hz, ±3 dB, measured anechoically at one meter on axis with swept one-third-octave pink noise. Maximum sound pressure level is 108 dB at one meter with 0 dBu into the balanced input.

The infrasonic filter is what makes the 100EL useful in real installations. The amplifier includes a sharp high-pass filter with a 12 dB per octave slope and a -3 dB point at 28 Hz. It is tailored specifically to the Sentry 100EL's response. Its job is to strip out subsonic energy that would otherwise waste amplifier power and push the woofer cone into excessive excursion. With cone movement and amplifier demand under control, program material can be played at higher levels without distortion and without giving up acoustic low-frequency response. The manual calls this one of the most important advantages of the integrated design. A separate amplifier would not have this filter, and without it the 100EL would be more vulnerable to overload and less capable of clean output at high levels.

The cabinet is a utility box finished in scratch-resistant matte black vinyl, with a steel-reinforced grille covered in custom gray cloth. Dimensions are 43.8 cm high by 30.5 cm wide by 29.2 cm deep - 17.25 by 12.0 by 11.5 inches - and the system weighs 15 kg, or 33 pounds. The cabinet is intentionally sized for rack mounting. With the optional SRB-7 rack-mount/wall-mount kit, the 100EL can go in standard EIA 19-inch racks or be mounted flush or at an angle on a wall. Electro-Voice even includes a second nameplate that can be applied over the original label when the cabinet is mounted inverted, with the woofer closer to the ceiling. The manual warns against mounting the 100EL by the back panel alone or by any single panel, because the panel may separate and the speaker may fall. The SRB-7 kit is strongly recommended for any non-standard mounting.

Ventilation matters. The metallic portion of the enclosure back works as a thermal radiator to keep the amplifier within design limits, and it is normal for this panel to get quite warm during extended high-level operation. The manual advises leaving at least one inch of space behind the panel for air circulation. It also says maximum temperature rise should not exceed 70 degrees Fahrenheit, though normal operating temperature is well below that. Don't bury this monitor in a sealed rack.

The front panel also carries a system level control that varies amplifier gain from zero over a useful range of more than 30 dB, plus a red indicator lamp that shows when AC power is applied. A replaceable AC fuse is on the rear panel. The domestic model draws a maximum of 120 watts from a 105-130 volt, 60 Hz line and uses a 1.5-amp slo-blow fuse. The export model runs on 210-260 volts at 50 or 60 Hz with an 800 mA slow-acting fuse.

Period advertising for the 100EL ran in the trade press through 1985 and 1986, with placements in Modern Recording (October 1985, p.11), Mix (August 1985, p.69; October 1985, p.171; April 1986, p.135), and DB Magazine (March 1985, p.15; May 1985, p.9). The copy is consistent across all of them. Electro-Voice pitched the 100EL as the monitor that provides its own power, fits in tight spaces, simplifies setup, and reproduces sound with test-equipment accuracy. The ads stress that the on-board amplifier makes the 100EL ideal for single-channel monitoring - why buy one speaker and an extra amplifier channel when the 100EL does the job by itself? - and that the integrated design reduces interconnect problems and eliminates power loss from lengthy speaker cables. This is marketing copy, not independent review. It does describe the design priorities that shaped the product.

The 100EL belongs to the Sentry family, which Electro-Voice positioned as a complete line of studio monitors. The Sentry 100A is the passive version: same 8-inch two-way design, same 45 Hz to 18 kHz response, same rack-mount capability, but no integral amplifier. The Sentry 500 is a larger 12-inch two-way with constant directivity, designed to broaden the sweet spot for multiple listeners. Electro-Voice's own literature calls the 100EL the fourth member of the Sentry family, filling the niche for engineers who needed a powered monitor for remotes, video editing booths, or any situation where rack space was at a premium. It is not a replacement for the 100A. It is a variant for a specific set of problems.

What the 100EL does not have is the kind of documentation that would let a collector trace serial numbers, production dates, or unit-to-unit variations. The manual and the advertisements survive, but service literature is thin, and there is no independent test report in the available record. The specifications are complete and internally consistent, which suggests they come from Electro-Voice's own engineering data, but they have not been corroborated by a third-party review. Collectors should treat the 50-watt rating and the 45 Hz–18 kHz response as manufacturer claims rather than independently verified measurements.

For anyone considering a 100EL today, the practical concerns are the same ones that faced studio engineers in 1985. The amplifier is matched to the speaker, which is good, but if the amplifier fails, the whole system is down until it is repaired. The thermal design relies on the back panel radiating heat, so the 100EL needs ventilation space and should not be enclosed. The infrasonic filter is a genuine asset for anyone pushing the monitor hard, but it also means the 100EL will not reproduce the deepest subsonic content - not that an 8-inch woofer in a 0.7-cubic-foot box was ever going to do that anyway. The high-frequency control offers useful room-tuning flexibility, and the balanced input makes it easy to interface with professional gear. The unbalanced input is there for convenience, but the manual's warning about not connecting a power amplifier applies to both.

The Sentry 100EL is a powered near-field that predates the modern powered-monitor boom by a decade or more. It was not marketed as a revolutionary product. It was marketed as a solution to a set of practical problems - limited rack space, remote recording, cramped video booths - and it solved them by putting a modest but well-matched amplifier into a speaker that was already trusted.