ProAudio Review - May 2008 - (Page 20) From The Road by Tom Young Line Arrays Good (But Not New) News or well over 10 years, speakers have seen a significant change in design with the use of “Vertical Line Array” systems. The idea of line array systems is not new at all. Actually, line array systems were used a lot in the 70’s with “column” design speakers. Does anyone remember a Bogen or Shure Vocalmaster PA? There were several issues that existed with column speakers, one being that large-wattage power amps weren’t available and eventually those systems were replaced with bi-amplified systems. With advanced speaker and driver design, larger power amplification, along with improved high frequency wave-guide horn design, line array systems have seen a major resurgence in the professional audio market and travel on all major tours. CORRECT USE As in all speaker systems, the main element for using a line array is to use it correctly. The solution to line array systems is how the drivers work together in multiple speaker configurations. The benefits of vertical line array systems are long throw coverage and low frequency directionality. When building the array, several speakers should point into the seating area farthest away from the stage, then adding angle between each speaker to provide coverage as you get closer to the stage. Usually, you would end up with only one speaker covering the area closest to the stage. As your speakers cover areas that are closer to the stage, you have fewer speakers pointing in that area. This contributes to why most vertical line arrays have a “J” type of look to them. High frequency horn designs are built to have a real narrow vertical coverage (normally five to 10 degrees), while providing coverage horizontally at a very wide angle (normally 90 to 120 degrees). The more the line array stays in a straight line, the better the directionality of the frequencies. When you take multiple low frequency cone drivers and array them together into a straight vertical line and all of the drivers are an equal distance apart and operating at the same volume and frequency response, the combination of the array actually causes lower frequencies to exhibit directionality in the vertical plane. Putting all of your lower frequency drivers in a row will provide increased output of the array while keeping lower frequency energy off of the ceiling. When calculating what frequency your directionality extends to, you have to consider only the speakers that are essentially in a straight line. Once the angle between speakers is more than about four to five degrees, you will lose the effect. By using a typical “J” array, you still keep a significant amount of low frequency sound off of the ceiling. Low frequency directionality is directly related to the vertical height of the line array, which is equivalent to the frequency wavelength of the lowest frequency that exhibits directionality control. HELPFUL SPECS Speed of Sound: 1130 ft. per second in air (rounded up) 20∞C Wavelength: 1130 ÷ frequency = wavelength (or 1130/Wave = Freq) So, let’s say you have 5,6 or 8 speakers in a straight line: 1130 ÷5 = 226 Hz/1130 ÷5 = 188Hz /1130 ÷8 = 141Hz This is helpful in making a quick determination on what you are achieving in LF directionality based on the size of your array. THE OMNI-DIRECTIONAL NATURE OF SUBS With subwoofers being omni-directional in nature of each element in the array, there is no front-to-back directionality. This can cause low end to spill onto the stage and interfere with the monitor sound you are trying to achieve. Currently, cardioid and hyper-cardioid subs are being used on tours and now more than ever you are seeing subs flown with the main arrays. Cardioid loudspeakers are two transducers separated by an exact distance within the enclosure, with delay on the rear driver, creating a directional radiation pattern. Cardioid subs have a maximum level cancellation straight back of 180 degrees behind them, while the hyper-cardioid have maximum level cancellation at or around 120 degrees off-axis. CHOOSING LINE ARRAY When considering a line array, the vertical coverage of this type of speaker is normally well controlled and fairly even in most systems offered today. The horizontal coverage varies as you move off axis of the vertical line array, and frequency response is not consistent from one product to another, so listen to the differences before making your purchase. In some venues the only hanging points are close to a theater wall, so a line array located close to a wall can be problematic for reflections. Also, in venues with balconies, the balcony wall can provide a direct reflective surface that cannot be avoided when hanging a straight line array. Additional benefits of choosing line arrays are found in touring load-in and set up. Hands down, line array speaker systems are easier and quicker to rig. Most arrays are rigged using only one or two motors and two crew members. The manufacturer designs of rigging systems are constantly improving based on end user comments. I see more and more vertical line array systems traveling on rolling carts with almost all of the rigging attached to the speakers. After attaching the main bumper bar and motor, it is ready to fly. There is no comparison to the time conventional speaker arrays require and additional parts needed to achieve similar results. Fewer speakers are required to get better coverage of your seating area using a line array as opposed to a conventional array. The distance requiring delays has been extended with long throw array designs. Also, with the size of the enclosures and box count required on the truck, it saves drastically on the trucking required to do a show or tour. And these days, with the cost of trucking and fuel the savings is significant. This is an exciting time to be mixing sound or designing sound systems with the options of speakers available today. The abundance of good speaker products has never been more evident. Manufacturers’ improvements to DSP control of these systems are constantly evolving, making more systems closer to plug and play. Tom Young is lead engineer for Tony Bennett. 20 | ProAudio Review | May 2008 www.proaudioreview.com http://www.proaudioreview.com
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