See the video review of the Acoustic Image Corus Combo Amp

Raleigh, North Carolina's Acoustic Image has built a reputation for quality and ingenuity in its highly portable amp designs. As its name implies, Acoustic Image is especially passionate about reproducing authentic, uncolored tones for just about anyone—guitarists, bassists, violinists, cellists, horn players—who wants to amplify an acoustic instrument. Acoustic Image's product line consists of four amplifier heads and three combo amps, and the 400-watt Corus combo is the company's recommendation for acoustic ax wielders who want to plug in.

Space-Age Polymers, Floor-Blasting Woofer

The first thing you notice when you haul the Corus from the box is its intriguing shape and high-tech polymer construction. Viewed from the front, the amp's rectangular profile seems run of the mill, but a bird's-eye view reveals its cool, modified-cylinder footprint. According to Acoustic Image, the shape—which is flat only on the front—results in a stiffer, tougher enclosure with minimal sound-coloring resonance, while the amp's strong, man-made materials make for a light schlepp to and from gigs and jams.

The Corus's front panel is packed with knobs and soft, rubberized push buttons—27 in all. Fortunately, they're laid out logically with large, easy-to-read labels. Along the left side are ¹/₄-inch/XLR combo inputs (with selectable phantom power) for each channel. Controls for Channel Two run (somewhat counterintuitively) along the top, and Channel One's appear below them. Both channels feature independent bass, mid, and treble controls, as well as convenient front-panel send and receive jacks for the independent effects loops—which allows you to, say, run your vocal mic through a fancy processor and into Channel Two while running your guitar clean or into its own effector. The right-hand portion of the panel features global controls, including a six-position selector and a level control for the built-in digital effects (flanging, "ambient" chorus, delay, and reverbs—hall, room, and plate). Back-panel controls allow you to connect the unit to a Corus EX extension cabinet ($519 list/$459 street) or any other four-ohm, Speakon plug-equipped cabinet.

Inside, the Corus is loaded with a ten-inch woofer that fires toward the floor to maximize bass response, while mids are distributed by a five-inch driver and treble frequencies arrive via a one-inch tweeter that you can disengage with a rear-panel rocker switch. A built-in stand on the bottom of the amp lets you angle it up toward your ears—a real boon for gigs where you don't have a monitor. The only tricky part is that the spring-loaded stand doesn't have a lock function and tends to slam back home when you're repositioning the cabinet.

Loud and Proud for Sensitive Types

I tested the Corus with a Durango B-46 slope-shoulder dreadnought with L.R. Baggs Dual Source electronics, a Taylor 615ce jumbo with Expression System electronics, a Breedlove Focus cutaway dread that also had L.R. Baggs Dual Source innards, and an Alvarez-Yairi WY1-12AE 12-string with the company's System 500 II electronics. Upon plugging in, it was immediately apparent that the Corus has more than enough crisp power and volume to hang with amplified bandmates. Naturally, high volume can lead to feedback, especially if your guitar's electronics include a microphone (as the Dual Source system does). However, I didn't find feedback to be a problem except at close range and in smaller environs. In such instances, the onboard notch filter worked like a charm.

While using the Dual Source–equipped Durango's onboard controls to mix between the bridge piezo and internal condenser mic, I found that the Corus provided less differentiation between the two signals than some amps do. Soloing the piezo provided a tad more treble response than the soloed mic, but the distinction was minimal throughout the range of the blend control. This is probably due to the amp's down-firing woofer—which is a definite boon for anemic guitars but also has a tendency to exaggerate bass. Turning the amp's bass knob to nine or ten o'clock avoided boominess and helped me get a little more leverage out of the mic/piezo blend. Likewise, engaging the tweeter and setting the mid control at ten o'clock added sparkle and avoided boxy, nasal tones.

Despite their different body styles and acoustic tones, the Durango, Taylor, and Breedlove guitars responded similarly when played through the Corus. All yielded rich, clean, delicate tones when my attack was gentle or moderate (and sounded especially pretty when fingerpicked), but each sounded a bit harsh when I dug in with a pick and attempted either straight-ahead, Johnny Cash–style strumming or more rocking fare. However, the Corus was more forgiving of energetic strumming on the Alvarez 12-string, perhaps because the added treble from the six unison strings crowded out the midrange frequencies that the Corus tends to disagree with.

Amps with built-in effects are usually limited in scope, and the Corus's are no exception. While they are all perfectly usable, the lack of parameter adjustment (other than the level knob) limits the utility of the chorus and flanging. But I was perfectly happy leaving the effect knob on the warm, spacious-sounding hall reverb setting, with the level set at two o'clock.

The Wrap

With its flattened cylinder housing, tough materials, and down-firing woofer, the Acoustic Image Corus distinguishes itself from other amps currently on the market. Its full-featured control set is convenient and easy to use, and its richly detailed, transparent tones make it an excellent choice for fingerstylists and others with a more measured attack. As this review was going to press, Acoustic Image announced that it will be introducing the Corus+, which will basically be the same amp as the Corus but with upgraded effects, a power increase to 800 watts, and a "Cabrio" feature that allows the amp head to be easily removed from the cabinet, so that each can be used separately or together.