Celestion SL700 (1982)

At 28 lbs per cabinet, it sits in the control room like a declaration—this is not a speaker built to please, but to reveal.

Overview

The Celestion SL700 isn't just another relic from the analog era—it's a statement of intent from a company better known for guitar speakers than studio monitors. Introduced in 1982, though not widely available until summer 1988, the SL700 marked Celestion’s bold entry into the high-end professional monitoring market. Developed in collaboration with audio engineer John Bird, the SL700 was engineered to be ruthlessly neutral, a tool for critical listening rather than sonic indulgence. Unlike most monitors of its time, the original SL700 was fully active, with built-in amplification in each cabinet—a rarity that gave it precise driver control and minimized signal degradation. This wasn't a passive box waiting for an external amp to breathe life into it; it was a complete, self-contained system designed to tell the truth, unvarnished and unflinching.

Despite being announced as early as summer 1987, widespread availability didn’t come until the following year, suggesting production challenges or limited initial runs. The SL700 was positioned as a compact nearfield monitor, aimed squarely at recording studios where accuracy trumps flair. Its design philosophy was clear: eliminate coloration, ensure time coherence, and deliver a flat frequency response that engineers could trust. That mission earned it the nickname “the truth speaker” among British studio hands during the late 1980s—a badge of honor in an industry where translation across systems is everything.

8" Doped-Paper Woofer in Sealed Aerolam Enclosure

Housed within a sealed-box cabinet constructed from Aerolam—a composite of aluminum sheets bonded to a honeycomb core—the 8" doped-paper cone woofer benefits from exceptional rigidity and internal damping. This construction minimizes panel resonance, a common issue in MDF cabinets, and contributes to the SL700’s tight, controlled bass response. While frequency extension dips below 55 Hz, measurements show the 32Hz band is down only 8dB in-room compared to 1kHz, indicating respectable low-end reach for a sealed design. The cast chassis adds mechanical stability, reducing unwanted flex during high-excursion passages.

1" Sonolex Dome Tweeter with Dished Aluminum Waveguide

Surrounding the 1" soft-dome tweeter (manufactured by Sonolex) is a patented dished aluminum waveguide, one of the SL700’s most distinctive features. This isn’t just cosmetic—it’s a functional innovation designed to control dispersion and time-align the drivers, ensuring a coherent acoustic center. The waveguide improves off-axis response, reducing early reflections from console surfaces and side walls, which in turn enhances stereo imaging and depth perception. The tweeter itself delivers smooth high-frequency reproduction up to 20 kHz, with a measured response of ±3dB from 80 Hz to 20 kHz.

Bi-Amplified Active Design with Internal 50W/25W Amplifiers

Each SL700 cabinet contains its own bi-amped electronics: 50 watts for the low-frequency driver and 25 watts for the high-frequency section. This integrated amplification eliminates the need for external power amps and allows for optimized tuning between drivers and crossovers. The amplifiers are housed within the same chassis, sharing the Aerolam enclosure’s structural benefits. While amplifier class and topology aren’t documented in available sources, the design ensures tight damping and excellent transient response. The system’s nominal impedance is 8 ohms with a 4-ohm minimum, making it compatible with a wide range of preamp outputs. However, because it’s active, the concept of external amplifier matching shifts from power delivery to line-level signal integrity—something later owners have grappled with when integrating the SL700 into modern setups.

Low-Order Crossover at 3.2 kHz with 6/12 dB Octave Slopes

The crossover network operates at 3.2 kHz, employing a 6 dB/octave low-pass slope for the woofer and a 12 dB/octave high-pass slope for the tweeter—a relatively gentle approach compared to the steep Linkwitz-Riley alignments common in passive designs. While some conflicting reports cite crossover frequencies as low as 2.5 kHz or 3 kHz, the 3.2 kHz figure from Stereophile’s technical review is the most consistently referenced. The shallow slope means both drivers operate in a transitional overlap zone, which can contribute to the slight thickening in the lower midrange noted by reviewers. However, this also preserves transient detail and reduces intermodulation distortion, aligning with the SL700’s goal of transparency over clinical precision.

Historical Context

Prior to the SL700, Celestion was synonymous with guitar speaker drivers—components found in guitar amplifiers used by rock legends like The Who and Jimi Hendrix. The SL700 represented a strategic pivot into professional studio monitoring, a market dominated at the time by American brands like JBL and Altec. The collaboration with John Bird brought a meticulous approach to crossover design and cabinet engineering, setting the SL700 apart from typical British hi-fi speakers of the era. Though it never achieved the ubiquity of the Yamaha NS-10, the SL700 found favor in elite UK studios including Abbey Road, Townhouse, and Sarm West. It shared the stage with contemporaries like the Celestion SL600, though the SL700’s active design made it a more specialized tool. Only two variants exist: the original SL700 and the SL700 SE—there is no SL700si, contrary to some online speculation.

Collectibility & Value

Today, the Celestion SL700 is a sought-after collector’s item, particularly among engineers who value its uncolored sound. Working pairs in good condition typically sell for $1,200 to $2,000, though fully serviced units command higher prices. Project pairs—non-working or in need of restoration—can be found for $500–$800, but repair costs add up quickly. One owner reported paying less than £500 for a pair with stands, while another listed a working set with original grilles and stands for $750. Sensitivity is rated at 82 dB/W/m (averaged between 200 Hz and 3 kHz), making the SL700 relatively inefficient and demanding of clean, robust preamp output. Owners have successfully driven them with tube gear like the Ampex 6973, though some question whether they require “lots of power” or are merely sensitive to source quality.

Common issues include aging electrolytic capacitors in the internal power supplies, which can lead to hum or complete failure. The built-in amplifiers, while robust, are prone to thermal stress and component drift over decades. Soft-dome tweeters are delicate and can be damaged by clipping or overdriving. The yellow Kevlar cones, while iconic, are susceptible to UV fading and surface cracking if exposed to sunlight. Restoration is possible but costly—re-capping, amplifier servicing, and driver reconing should be handled by specialists. Some owners controversially convert the SL700 to passive use by removing the internal amps, preserving the cabinet and drivers while bypassing the aging electronics. Despite its strengths, the SL700 isn’t flawless: one reviewer noted a “thickening in the bottom of the lower midrange,” and while the overall assessment was positive, it came with the caveat that “there were still some problem areas.”

eBay Listings

Celestion SL700 vintage audio equipment - eBay listing photo 1

Celestion SL700 FOO Bookshelf Speakers Pair Vintage UK Audio

$1,204

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