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ATC SCM20SL Passive Closefield Monitors

Passive speakers seems to be a vanishing species in the professional studio realm, but there are plenty of us out there who believe the best speaker and the same amp cannot be put into the same cabinet.

Passive speakers seems to be a vanishing species in the professional studio realm, but there are plenty of us out there who believe the best speaker and the same amp cannot be put into the same cabinet. There are plenty of good-sounding powered monitors from Genelec, JBL, ATC, Klein + Hummel and others, but there exists a class of passives that are incredible accurate and designed for critical listening.

FAST FACTSApplications

Recording, post production, broadcasting

Key Features

Two-way, acoustic suspension; six-inch polyester-weave woofer; 1-inch soft dome tweeter; bi-wire speaker connectors; 45 Hz-20 kHz frequency response


$3,00 per pair


ATC/Transaudio Group | 702-365-5155



• Accurate • Low listener fatigue

• Excellent imaging • Good bass with natural-off


• May be too pricey for the mass-produced, active-monitor minded


A great-sounding passive speaker that fits into any critical listening

application — but you need an amp!

Case in point, the ATC Passive 20. This acoustic suspension, two-way with proprietary six-inch woofer, 1-inch neodymium tweeter, is a very accurate speaker that is easy to drive with most any amplifier. You put a high-end amp in front of these speakers, and the ATCs create a perfect tool for analytical listening applications: tracking mastering, post production — even high-end broadcast.


The ATC Passive 20, priced at $3,000 a pair, is seemingly a conventional two-way, but it is built with top-grade components including the 1-inch soft dome tweeter, 6-inch polyester-weave woofer and a 2.8 kHz crossover network. Because of the proprietary, low distortion woofer that is built in-house at ATC, speaker sensitivity is only 86 dB/1W/1m. Thus, you will need an amp with plenty of power, which is not a problem with today’s amps. Nominal impedance is 8 ohms.

Factory-rated frequency response is rated at a very tight, ±2 dB window) 70 Hz -17 kHz, and 45 Hz – to 20 kHz within a 6 dB window; pretty darn impressive for a small, non-ported speaker.

The heavily braced cabinet eliminates unwanted, resonances that can blur the sound. The cabinet edges are features beveled edges to reduce sound diffraction. Each speakers weighs 40 pounds and it measures 19 inches x 12 inches x 16.5 inches).

Around back, ATC include connections for single pair cables or biwireable, spades or banana plugs. Nice. Everything seems high quality with this speaker.

ATC makes optional stands and wall mounts for Passive 20s, but they are not cheap.

In Use

I used the ATC Passive 20s with three amps. I first connected to the Bryston 14B SST. I used Alpha Core solid copper speaker cables. Sources included 24-bit/192 kHz acoustic guitar recordings, and a number of reference SACDs and DVD-As played through the Vacuum State Electronics modified Sony SCD-777ES SACD players or the Esoteric DV-50 universal player. All sources were routed through a Legacy/Coda high current monitor preamp using balanced Westlake Low PE cables. I also played back through the reference Pass X350.5 amplifier.

I also installed the speakers into my Apple G5 work station monitor system, powering the duo with one of those cheapie Behringer studio amps you can buy for a couple of hundred bucks. The source was the G5-based BIAS Peak software at 24-bit, 96 kHz, played through a Benchmark DAC-1 D/A.

With my big rig and the ATCs, I listened to recordings of various vintage Martin guitars and a Gibson jazz guitar, the ATCs immediately showed-off their accurate presentation and lack of color. I could hear all of the string squeak and other transient information of the acoustics that high res brings out; the imaging is excellent. Most of the reverb tail decays and other audio subtleties that I hear on my reference, much larger Legacy Focus 20/20s were relayed by the ATCs.

On jazz, pop and classical recordings, the uncolored accuracy was apparent — not a hint of tweeter zinginess and edge that can result in ear fatigue. For a small box, acoustic suspension speaker the bass was ample and tight with out mid bass bump. In listening to female vocals, I did not hear any sibilance from the tweeter.

The longer I listened the ATC, the more they became a great analytical tool. A low-distortion, linear speaker and high quality amp makes it easier to listen at higher levels for longer period of time. Many cranked-up powered speakers — where the amp design is often a compromise — wear me out.

The speakers even sounded good with the coach-class Behringer A500 amp at low-to-moderate levels, though the transients sounded edgier than, as you would expect, than the Bryston or Pass.

I had no complains at all about the ATCs. Though not as efficient as other passives I have tried, my 350 – 700 watts per channel range of amps did not bat an eye. The speakers’ cables were easy to hook up, the speakers fit right onto my Apollo custom stands. They were not overly heavy.


In this day of active monitors, it’s nice to see and hear a well-designed passive speaker for those of us who swear by separates. It is very accurate, images well and does not hurt your ears when cranked up. The ATC Passive 20s are not cheap, but really good things in life usually aren’t. Highly recommended.

Review Setup

Bryston 14B-SST bipolar output stereo amplifier, Pass X350.5 MOSFET output stereo amplifier, Behringer A500 amplifier; Legacy/Coda High Current Monitor Preamplifier; Alpha Core and Westlake cables; Apple G5, Lynx L22 PCI card; Benchmark DAC-1 D/A.