Compact Line Arrays
Nov 1, 2003 12:00 PM, Mark Frink
The list of large-format line array speakers introduced during the past decade is well known and well used. But a new generation of compact systems has emerged to provide smaller venues with the benefits garnered from line arrays. Everyone recognizes the limitations of the big guns: weight, size, cost, and limited ability to bend in a vertical arc have kept line arrays from being much more than a curiosity in smaller venues, where traditional modular speakers are better suited. Compact line arrays better fit smaller budgets and venues so that a wider audience can enjoy the near-field listening experience.
HOW DO LINE ARRAYS WORK?
There's been much discussion about how sound from an infinite line source defies the inverse square law: instead of attenuating by 6 dB for each doubling of distance, it only attenuates at 3 dB. This propagation of sound is described as a cylindrical wave front instead of the usual spherical wave front generated by traditional speakers and horizontal arrays. As a practical matter, this cylindrical behavior exists only in the near-field of a line array, where a tall column of closely coupled speakers addresses listeners through a relatively large angle. At farther distances, the array loses its tight vertical-pattern control. This happens at shorter distances of a few yards for the lowest frequencies and farther away at progressively higher frequencies. At the highest frequencies, the near-field effect extends out past 100 feet.
This phenomenon provides improved sound quality in arenas; in smaller rooms, it can guarantee fantastic sound to all seats, provided that the venue's geometry is appropriate. A line array's horizontal coverage is fixed, depending on the manufacturer's design, at somewhere between 90 and 150 degrees wide. If the venue is wider than that, it must have the side areas addressed by additional side arrays or fill systems. Furthermore, the venue must have hanging points at a sufficient height to get a line array up and properly aimed. Smaller, lighter boxes make this possible in rooms where large-format line arrays would not be practical.
The sound's coherence that is provided by a line array is startlingly clear, as the array elements are vertically arranged so that there is no interference from one enclosure to the next. The coverage throughout the listening area can be smooth and consistent from one seat to the next, and the difference in sound level can be just a few decibels from front to back. This improved sound quality enhances the stereo image so that it can be enjoyed throughout a much larger listening area, not just down the center of the room. A line array can exhibit great pattern control to provide fewer unwanted reflections off ceilings and walls, as well as greater gain-before-feedback for open mics onstage.
WHY A COMPACT SYSTEM?
The limits to using line arrays in smaller venues include their weight and height. Smaller, compact enclosures are not only less expensive, but they also weigh less and are easier to curve in an array. Due to coupling issues (for fundamentals on coupling, see the sidebar “Understanding Coupling” on p. 46), there is a limit to how much of an angle can be placed in an array from one enclosure to the next. Beyond about 5 degrees, the highest frequencies no longer couple together and they instead start to beam, which provides spotty coverage from one elevation to the next.
The advantage that smaller cabinets have is that their arrays can bend for more vertical coverage in a shorter height. In smaller venues, it's not unusual to need 20 degrees of uptilt at the top of the array and even more to get down to the front of the audience: ten cabinets might need an average splay of 5 degrees just to make this coverage.
The pattern control provided by line arrays extends down to the lower frequencies as a function of the array's height. Arrays lose vertical-pattern control at frequencies whose wavelengths are longer than the array's height. To achieve pattern control down to 100 Hz, for example, an array must be more than 11 feet tall and with a typical cabinet height of a foot or less; control down to 100 Hz means using ten or more cabinets in an array.
Most compact line arrays are not designed to serve as standalone systems but are intended to be supplemented with subwoofers for full-range response. Most have purpose-designed subs that can be integrated into flown or stacked arrays. Although manufacturers recommend arrays employing a minimum of four to six cabinets to achieve pattern control down to their lowest octave, there is no rule that says that they cannot be employed in short arrays or even by themselves. In fact, some of the smallest models have been successfully used as underbalcony and front-fills because of their physical height and horizontal coverage. Other uses for compact line arrays include short arrays as delay zones for distributed systems in large convention centers or as a surround system because of the wide horizontal coverage area of each array.
Interested in purchasing a compact line array? The following information will help you get started; visit manufacturers' Web sites for more.
Adamson's Y-10 employs a JBL 1½-inch exit compression driver coaxially mounted with a proprietary 9-inch Kevlar midrange compression driver. On either side of the mid-high chamber is a 10-inch woofer.
Apogee was the first manufacturer with a modular line array product, the ALA-3, which employs dual 10s with a pair of conical horns for its two 1-inch compression drivers between them.
Bose has been building line array systems for quite some time. Although the concept is basically the same as other products in this article, the execution is different. The Panaray MA12, with 12, 2¼-inch drivers in a single extruded aluminum enclosure, is designed primarily to reproduce the vocal range (155 Hz to 12 kHz). Accessories include a digital controller, EQ cards for use with Bose amplifiers, and a transformer for 70/100V systems.
d&b audiotechnik's entries into the compact line array field are the passively crossed-over, two-way Q1 and Q7. Both are the same physical size and weight and have the same driver configuration — a 1.3-inch exit HF driver and two 10-inch LF drivers in a dipolar arrangement. The Q1 HF driver is fitted with a toroidal waveshaping device with a 75-by-15-degrees coverage pattern. The Q7 loudspeaker has a rotatable 75-by-40-degrees conventional CD horn for use individually or in columns with Q1s. Weight is 49 pounds each, and maximum SPL is 139 dB for Q1 and 138 dB for Q7.
EAW's Digital Steerable Array (DSA) Series is similar in appearance to the Bose MA12, and the enclosure is manufactured of extruded aluminum, as well, but that's pretty much where the similarities end. The DSA is a self-powered system that employs digital signal-processing technology to vary the vertical pattern from 15 to 120 degrees as well as aim the coverage ±30 degrees. The KF730 is a three-way, biamped speaker whose entire face is the mouth of a mid-high horn for its dual 7s and dual 1-inch exit compression drivers. Ten-inch woofers are mounted on the two ends of the enclosure.
Electro-Voice's Xlc 127+ is a triamped, three-way enclosure that uses two of the same compression drivers as the larger X-Line. Its asymmetrical design places a single 12 at one end, a pair of horn-loaded 6.5s at the other, and a pair of NDym compression drivers on plane-wave generators down the center. The Xlc 124 is the down-fill version, and the Xlc 118 is a companion single 18 subwoofer designed to be flown in adjacent arrays or integrated at a 2:3 ratio.
JBL's VT4887 is a smaller version of its original large-format VerTec based around dual 12s instead of 15s and using the same type of pinned hinge bars for rigging. JBL's smallest VerTec, the VT4888, is a biamp, three-way dual 8 enclosure whose quad 4s are passively crossed over to dual 2407 ring radiators. The VT4881 is its companion single 15 subwoofer. All three of JBL's VerTec line array elements can be self-powered by the addition of a Crown-manufactured Drive-Pack.
The ISP Technologies Reference Line 210 is a triamplified line array incorporating a 4-inch diaphragm midrange compression driver and two 1¾-inch polyester diaphragm compression HF drivers. The low frequencies are handled by a pair of slot-loaded 10-inch woofers.
L-Acoustics' dV-DOSC is one-half of the mid- and high-frequency section of its large-format V-DOSC cabinet, the original line array. The triple 15 companion dV-Sub uses the same drivers as the V-DOSC and is intended for use at a 1:3 ratio to provide identical response in small arrays.
Martin Audio is the only company with all horn-loaded line array solutions, and like its large-format W8L, the W8LC is triamped. Its individually horn-loaded elements are able to provide even horizontal coverage down to 500 Hz. Even smaller is the W8LM, which features an evolution of Martin's Hybrid loading technique. The driver complement is 2-by-8-inch for LF and low-mids and 2-by-1-inch HF in a three-way active/passive design.
McCauley's M-Line is a two-way speaker that comes in three models with three different high-frequency horns. Nominal vertical coverage of 60, 90, or 120 degrees allows designers to create systems with high-frequency coverage tailored to a listening area by employing narrower horns at the top and wider horns at the bottom. The company's In.Line is similar to the M-Line, but it is designed only for permanent installs. The In.Line features a simplified rigging system to save weight and cost.
Meyer Sound's M1D is a self-powered biamped enclosure employing dual 5s and triple dome tweeters. Like all of its dual-woofer speakers, one driver is lowpassed to provide more even midrange coverage. A companion dual 10 M1D subwoofer is also available. The company's M2D is a self-powered, dual 10 enclosure that employs an amplifier package similar to the powered UPA and the same compression driver as Meyer's CQ-2. The companion self-powered dual 15 M2D Sub is easily integrated into arrays and packs twice the power of the 650-P. At 235 pounds, Meyer's new dual 12 MILO is a bit heavy to be called compact, so it fits at the top end of this category. It features a single 1.5-inch compression driver, and above 4 kHz, three 0.75-inch compression drivers take over to provide plenty of highs for long throws. The MILO can easily be integrated into M3D and M3D Sub arrays.
The Nexo Geo S805 uses a single 8-inch woofer passively crossed over to a 1-inch driver mounted on its patented Hyperboloid Reflective Wavesource. The S830 is a companion down-fill module with 30 degrees of vertical coverage; its companion subwoofer is the CD-12. Nexo's new Geo T4805 employs dual 8-inch drivers as well as another pair of rear-firing 8-inch drivers, lowpassed at 250 Hz, that create cardioid coverage in the low frequencies and contribute to forward pattern control. Its unusual rigging system, designed by SSE director Chris Beale, comprises the T2815 down-fill box that provides 15 degrees of vertical coverage and the companion CD-18 subwoofer.
Renkus-Heinz's new PNX 102/LA is a two-way enclosure with dual 10s and dual 1-inch exit-compression drivers that boasts 150-degree dispersion with no horn loading. It can also be ordered as the self-powered PN 102/LA enclosure, which has an R-Control supervision network and weighs an additional 10 pounds.
The SLS RLA2 uses its distinct RLA-1000 ribbon driver to provide a smooth high end; coupled with other array elements, it can be used as a planar line source. Though it can run as a biamp system, when ordered with NL-8 connectors, the cabinet can be triamped and the outside woofer lowpassed at 300 Hz to improve its horizontal coverage in the mids.
Mark Frinkis Mix's sound reinforcement editor.
Coupling, the mechanism by which a line array works, is familiar to anyone who has assembled large quantities of speakers into systems. Coupling between transducers occurs when the distance between their acoustic centers is less than half a wavelength. The best case for 12-inch speakers, with their drivers nearly touching, can provide coupling up to about 550 Hz. For 10-inch speakers, coupling can occur up to 630 Hz, and for 8-inch speakers, coupling can extend up to 800 Hz. (This is why simply putting a hand's width of space between adjacent speakers in a traditional array attenuates the mids.)
At higher frequencies, the drivers' acoustical centers must be even closer for coupling to occur. For coupling clear up to 20 kHz, acoustical centers of adjacent drivers would need to be a fraction of an inch. Clearly, this requirement makes it impossible to create line sources with high-frequency coupling, unless there's another way to couple the output of drivers.
Modular line array developer Dr. Christian Heil has shown that the output of individual compression drivers' horn mouths can couple when their output is in phase at all points of the mouth's cross-section and when they are in close-enough proximity. The patented DOSC waveguide is his solution for high-frequency coupling from the openings of tall, thin isophasic horn mouths. Different manufacturers have come up with their own waveguides to vertically couple high frequencies from one speaker module to the next, while others have abandoned line array principles at higher frequencies. Readers should understand that it's possible, and sometimes even prudent, to employ a hybrid design that provides low-frequency coupling, while employing multiple horn elements for high-frequency pattern control when an array must be bent more than a few degrees per cabinet. There are line array speakers that, strictly speaking, do not behave as line source arrays at all frequencies.
For More Information
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