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Absolutely Sound

April 1, 2006
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Few things can get a room full of engineers into a heated debate as quickly as the subject of monitors. Which are the best? Should they be extremely accurate or should they sound like a typical home stereo? Do you carry your speakers with you from studio to studio? Do you mix on close-fields or on the room's mains?

Even for a professional engineer, listening is a highly subjective experience. The hearing mechanisms of our ears are as unique as our fingerprints, and the relationship between the acoustics of our pinnae, the electrochemistry of our auditory nerves, and the psychology of our brains is absurdly complex. Pity the poor speaker charged with delivering audio to such a setup!

FIG. 1: Close-field monitors should be arranged in an equilateral triangle with the engineer''s head at a distance of -approximately one meter. That -arrangement makes the direct sound more prominent than room -reflections, -minimizing the influence of room -acoustics on the engineer''s judgments.

There are, nevertheless, some objective truths about the way speakers are designed, the way they interact with a listener and a room, and the way to use them wisely in a typical project studio. Armed with these facts, you can decide for yourself which ones will work best for you and, just as important, which side you'll take the next time you're locked in a room of bickering engineers.

High Fidelity

A high-fidelity audio system is one that delivers the sound of a CD or other playback source with extreme accuracy. Ironically, the term hi-fi has come to mean a playback system that simply sounds pleasing to the listener; when you're listening recreationally, if your home-stereo speakers sound great to you, that's good enough. They may be deliberately designed to enhance bass and treble and give the overall sound more kick and sizzle. They may compress a recording's dynamic range, emphasizing its ambience, which isn't necessarily a bad thing in a living room filled with sound-sucking sofas and carpeting.

When you're tracking and mixing, however, it's your job, and not your speakers', to make things sound good. Most engineers feel they need a monitor system that gives them the aural truth. Many novices who try to save a few bucks by using their home-stereo speakers in a home studio are ultimately frustrated by mixes that never sound as good in other rooms. It's a simple equation — if your playback system emphasizes bass, your mixes will sound thin on speakers that don't have that same characteristic.

The quest for accurate monitoring is complicated by the fact that once the sound leaves the speakers, it bounces around the room on its way to our ears. Actually, our ears expect and depend on reflected sound to give shape and space to what we hear. (In an anechoic chamber, where there are no audible reflections, nothing sounds natural.) The problem is that reflections can combine to create standing waves and comb filtering (see “Square One: Standing Tall” in the January 2005 issue of EM). The best speakers will sound awful in a room with poor acoustics.

The proper solution, then, is to build a room and a speaker system that match each other perfectly. That is the approach taken by major recording studios. The mains are ordinarily large speaker systems set into the walls of a custom-built and carefully tuned room. Most project-studio owners don't have the budget or physical space for that, so most of us use close-field monitors.

Nearer My Heart

The term close-field, or near-field, refers to speakers in relatively close proximity to the listener. More specifically, close-field monitors are intended to be placed about a meter from your ears.

The theory behind close-field monitoring is that direct sound will prevail over room sound when speakers are closer to your ears than they are to any reflective surfaces. That is a tremendous benefit in a typical small room, in which acoustic disasters often occur. Note, however, that having close-field monitoring does not entirely remove the room factor from the equation. It is still important to position the monitors correctly and to treat the room's acoustics (see “A New Approach to Personal-Studio Acoustics” in the April 2004 issue of EM).

Close-field monitors should form a triangle, with your head at the bottom point (see Fig. 1). The distance between the monitors should be approximately one meter — the same as the distance from each monitor to your head. The monitors should be far enough away from the walls to avoid bass buildup, and they should be equidistant from the side walls, because asymmetric reflections would cause the two speakers to have different effective frequency responses. If the room is too small to allow the monitors to be placed far enough from the front wall, it may be best to place them very close instead. That will at least cause the bass buildup to be more evenly distributed.

Two Ways or Another

Close-field monitors commonly use separate drivers, or speakers, for high and low frequencies, and may sometimes use a third for midrange. Those 2- or 3-way designs, as they're called, are more cost-effective because of their use of specialized components. It's far easier and cheaper to build a small tweeter to handle the high end and a larger woofer to cover the low end than to build a single driver capable of covering the entire audible spectrum.

The signal is split into complementary frequency bands by a crossover, a combination of a lowpass and a highpass filter (and a bandpass for a 3-way design). If the crossover acts on the amplified signal, that's called a passive crossover. In an active design, the filtered signals feed separate amplifiers. The design of the filters and the choice of crossover frequency are key factors in the smoothness of the monitor's frequency response.

FIG. 2: A subwoofer can be used to extend the low-frequency response of compact close-field monitors. A crossover redirects low bass from the left and right monitors and sums them together to be reproduced by the subwoofer.

Even with 2- and 3-way designs, close-field monitors are generally incapable of reproducing low bass content, ordinarily rolling off below 50 Hz to 60 Hz. To cover the bottom octave and a half, engineers often add a subwoofer. Another crossover redirects the lowest part of the audible spectrum to the subwoofer. Although it's possible (and advisable, in the view of some experts) to set up stereo subwoofers, it's more common to sum the left and right channels to a single sub (see Fig. 2).

Conventional wisdom says that since bass frequencies are less directional, it doesn't matter where you position a subwoofer. But if you close your eyes and listen carefully, you can almost always locate a subwoofer by ear. For that reason, it's better to place the subwoofer between the left and right monitors at the same distance from the mixing position when possible.

Devil in the Details

Quality monitors are built of nonresonant materials, most commonly medium-density fiberboard, to ensure that the box itself doesn't color the sound. Designs with rounded edges and smooth surfaces help the sound disperse evenly. Although you are meant to listen from the sweet spot at the point of the aforementioned equilateral triangle, the sound shouldn't change too much when you reach left or right for a fader or mouse. A monitor's off-axis response, like a cardioid microphone's, should change smoothly and only slightly from on-axis.

If a tweeter and a woofer are attached directly to the front of the speaker cabinet, the smaller tweeter is closer to your ears by at least a couple of centimeters, causing high frequencies to arrive earlier than the lows. To compensate, some monitor designs align the signals, either by recessing the tweeter or electronically delaying its signal.

Increasingly, monitors are being built with integrated amplifiers. Although some engineers favor unpowered monitors driven by external amps, these powered monitors offer the convenience of matched amplifiers and drivers. If you take your own monitors to different studios to ensure a consistent reference, built-in amplifiers remove one more variable.

Concurrent with the popularity of the project studio, the market for close-field monitors has grown, and their quality has improved greatly. Many respectable models are now available in a variety of price ranges. The irony is that close-fields originally provided a “real-world” reference that engineers used to see whether the work they'd done on the mains would translate to a home system, and now we expect them to provide the accuracy required for critical work. Fortunately, well-chosen and well-placed close-field monitors are a viable solution.


Brian Smithers is Course Director of Audio Workstations at Full Sail Real World Education in Winter Park, Florida, and the author of Sonar 5 Ignite! (Thomson Learning, 2005).

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