- There's a line in a Toad the Wet Sprocket song that I've always thought was particularly well crafted: "You bend your words like Uri Geller's spoons..." For those readers too young, too old, or only recently paying attention, Uri Geller was the Dutch magician who claimed to be able to bend unsuspecting silverware into knots by sheer mental power alone-no physical contact was required. Hold that thought.
- Meanwhile, it's going on five years now since I admonished the faithful readers of SCN to "Be afraid. Be very afraid...we have now entered into the first well-defined audio epoch of the new millennium-the Age of the Line Array." As we all know, in the interim the line array has moved on to become the audio equivalent of the ubiquitous SUV, a very good choice for certain environments, but used everywhere regardless.
- Marketing voodoo has already transported some of the "well-known" artifacts of linear-array performance directly into the realm of audio myth. This is especially true of the simple, nonqualified statement claiming that line arrays only lose 3 dB per doubling of distance from the array. (This contrasts with the long familiar 6 dB fall-off per doubling of distance due to inverse square law.) The problem with the blanket statement of 3 dB fall-off is quite simply, that it is a blanket statement, and line arrays come standard with a whole plethora of wavelength related "it depends" clauses regarding their performance.
- However, it is quite refreshing to note that amidst all the hype and hyperbole there's a subset of the line-array family tree that's quietly revolutionized the design, implementation and performance of sound systems in highly reverberant spaces, the steerable array. Quick-how reverberant would a cathedral be if you removed the roof and walls? Now hold that thought as well and ask yourself-so what do Uri Geller and deconstructed cathedrals have to do with each other?
- We're used to aiming things by "pointing" them at their target; think satellite dishes, firearms, loudspeaker arrays, and even "standard" linear arrays. The linear array may be articulated (curved), in fact there may be sections of different curvatures (by varying spacing between elements) in order to modify vertical coverage performance, but the overall aiming is still done by physically tilting the array.
- Now what if instead of physically aiming the array, you could "bend" it some other way, perhaps like Mr. Geller, simply by using mental prowess? Luckily in this case it's not a matter of some paranormal prowess that's required, but merely an understanding of the physics required to "steer" the beam and a system that allow the implementation of that physics. In fact, antenna designers have been using the same techniques to "steer" the aim of fixed antenna devices for years. What's required are arrays comprised of identical elements/devices, and a means of controlling the initial time of propagation for each element in the array in order to "steer" the pattern up or down.
- All right, so now you see where Uri Geller comes in, but how does that relate to arrays and this cathedral question? Well, we know a few things from Olson and Beranek:
- 1. At some frequency/wavelength (Vf) related to the length of the array, low-frequency vertical pattern control will begin.
- 2. At some frequency/wavelength (Hf) related to the dimensions of the individual array drivers, horizontal pattern control will begin.
- 3. At some frequency/wavelength (Lf) related to the spacing of the individual array drivers, pattern control is lost and lobing will begin.
- Consequently, below the wavelengths represented by (Vf) and (Hf), the array pattern can still exhibit substantial energy distribution to the rear and sides of the array.
- So consider what happens to the energy emitted from our array when it is "tilted" to aim its energy downwards; the frontal energy is tipped down, hopefully into the audience, but the rear energy is now being tipped up, and directed towards the upper walls and ceiling. In a highly reverberant space (the aforementioned cathedral), the directive energy in the speech range, which is going to the audience, is being countered by the uncontrolled rear energy energizing the room's reverberant field.
- Counter that scenario with the performance of the "steered" array. In this case, the "beam" is steered downwards by progressively delaying the array elements from the top to the bottom of the array. The important factor, which isn't necessarily intuitive, is that in this case all of the energy from the array is steered downwards, not just the frontal energy. Leaping back to the question about the reverberation time in a room sans walls and ceiling, it's fairly obvious that the answer would be: none. So what if those surfaces were minimally or perhaps never energized by our steered array, which is putting all of its energy downward and into the audience? In an ideal world the answer would be similar to that of the missing boundaries, hence zilch with the reverberation time already. Then again, since we're not in an ideal world, our mileage may vary...but the trend will continue to be in our favor.
- Of course, the other obvious benefit of steering the array rather than tilting it is the aesthetic one, the array can be mounted vertically on a building boundary surface such as a front wall, a column, etc., and remain architecturally unobtrusive while still directing energy into the seating. The downside? Limited bandwidth and output level, but since the primary application of these systems is to provide adequate speech intelligibility in acoustically difficult spaces, those factors are not usually a limitation. So while you mull these things over, best wishes for a great New Year, and see you next time.
- TOA's HX-5 Series
- TOA Electronics' HX-5 series provides versatility in public address systems in a variety of venues. The series offers a variable dispersion angle that can be set for 60, 45, 30 and 15 degrees. Modular HX-5 speakers can be combined by stacking four speaker modules with a total driver complement of 4 woofers and 12 tweeters positioned along the baffle surface, allowing variable directivity control and low-frequency dispersion control. When two or multiple modules are connected to configure an arc, they function as an immense single speaker, allowing public address functions to demonstrate intelligibility in environments with long reverb times.
- Meyer Sound's MICA Loudspeaker
- The MICA is the smallest in the MILO line from Meyer Sound, suitable for touring, rental and fixed installation, or any applications that do not require quite as much power and throw distance as MILO, or where weight and size are a concern. It exhibits flat frequency and phase response across its operating range of 60 Hz to 18 kHz. It covers low and mid frequencies with two neodymium magnet 10-inch cone drivers with 2-inch voice coils, while the high-frequency section is located at the center between the two cone drivers and consists of two neodymium-magnet compression drivers with 3-inch diaphragms and 1.2-inch exits.
- SLS Loudspeakers' LS6593 Series
- SLS Loudspeakers' LS6593 series includes the LS6593S, a straight line array with controlled vertical dispersion, and the LS6593A, with internally articulated driver elements that allow wide vertical dispersion at one end of the array. The series is based on a woofer line array mounted on a front panel with a coaxially positioned ribbon tweeter array. The woofer array consists of 6 x 5.25-inch drivers while the tweeter array consists of 9 x 3-inch ribbon planar drivers driven from a passive crossover point of 2,000 Hz. The system delivers a frequency response of 80 Hz to 20 k Hz with an SPL of 94 dB referenced at 1W/1M and a calculated response of 118 dB continuous and 124 dB peak.
- Renkus-Heinz's ICONYX Loudspeakers
- Renkus-Heinz's ICONYX (IC series) digitally controlled column loudspeakers employ line array techniques, but differ from conventional line array designs. Six models are available in 8-, 16-, 24- and 32-channel sizes to suit different needs, such as houses of worship, transportation terminals and similar venues. All are constructed from the IC8 8-channel module. The modules are joined together in the field to form the IC16, IC16/8, IC24, IC32 and IC32/16. DSP software and true digital amplification enables the designer or operator to define the shape and aiming of the vertical beam without moving the IC columns from their installed position. Horizontal dispersion is fixed at a nominal 150 degrees between -6 dB points.
- Martin Audio's W8LMD Cabinets
- Martin Audio's compact W8LMD features a 20-degree vertical dispersion to cover a wide area, and can be used individually and in limited quantities for throw applications of less than 30 meters, or as a downfill cabinet for the W8LM. Using one or two W8LMD cabinets at the bottom of a W8LM array allows the system to throw further with the W8LMD's 120-degree dispersion covering front row central and the extreme front left and right. In arrays of one to four cabinets, the W8LMD can be used over smaller distances and coverage areas that require a large vertical angle.
- Electro-Voice's Xlc Line Array
- Electro-Voice's compact line-array, Xlc, allows for easy setup and transportation without compromising sonic capacity. The XLC127+ is a 3-way design that utilizes a 12-inch vented LF, 2 x 6.5-inch MF transducers on a 120-degree horizontal waveguide, and 2 x HF transducers that combine through a vertical plan wave generator to a 120-degree waveguide. The system can be used in tri-amp mode, or bi-amp two-way using the internal passive MF to HF network.
- JBL Professional's VerTec DP Series
- JBL Professional's VerTec DP series is compatible with Harman Pro Group's HiQnet System Architect software and feature JBL DrivePack technology, with remote control and monitoring capabilities. The VT4888DP line array and VT4882DP subwoofer are available with optional network input modules that allow JBL VerTec DP series systems to link into the HiQnet system. VT4888DP-AN and VT4882DP-AN feature analog audio XLR inputs. VT4888DP-CN and VT4882DP-CN feature digital audio and single cable control, and are Cobranet-compatible.
- EAW's KF730 Line Array
- EAW's KF730 line array module packs a six-driver, horn-loaded design into a compact enclosure. The full-sized mid/high horn fills the entire face of the enclosure, ensuring broadband 110-degree horizontal pattern control, which is extended by the Phase Aligned LF into the LF. A bi-amplified powering configuration (passive mid/high) reduces total system cost and complexity. The size and configuration of a KF730 series array defines its vertical coverage. Users can quickly and easily construct vertical arrays ranging from 4 to 18 enclosures.
