Line Arrays - Fad or Future

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Line Arrays - Fad or Future Printed in Live Sound International By Dave Rat

I get asked a lot of sound questions. Some are aimed at unraveling an understanding of a particular function, feature or concept while others are directed toward distilling my opinion on certain pieces of gear, methods or industry trends. The difference between the two query types is that there are relatively 'correct' answers to the former and the answers to the latter are just opinions that tend to be un provable. The answer to the question I was recently asked "Are line arrays truly better and here to stay or just the latest fad?" lays somewhere in between the two. Just in case you have been sleeping for a decade or are not a sound industry human, line arrays have taken the pro-touring industry over by storm. Nearly every manufacturer offers several line array choices and of the two manufacturers that I know of that do not offer them in their product line, both have been forced to take defensive vocal positions justifying why they do not. So, what is it about line arrays anyway that has positioned them to so completely dominate our industry? Stepping back and taking look, I see that there are several aspects that are quite clear and a one in particular that is not so apparent but the most important of all.

There are currently two basic approaches to sonically covering acoustic spaces and I will refer to them as 'centralized' and 'localized.' The centralized approach attempts to blanket the acoustic space with sound by implementing clusters of speakers that are physically located somewhat near whatever it is that the audience is supposed to be watching. More simply; put a bunch of big speakers near the band and point them at the audience. The 'localized' method of providing sound deals with the acoustic space by dividing it up into multiple regions that each have there own speaker or small sound system. This approach of placing many small speakers all over the place is not very common for rock shows but it is popular for airports, convention centers and other spread out areas that do not require a central focal point of listener attention

Since distributed systems tend to lack the aspect of providing a clear and defined auditory central focal point and I specialize in sound systems for rock shows that are all about getting everyone to focus on the central focal point, usually being the band, I am going to personally focus on the centralized method of sound reinforcement in the words to follow.

The method or design implemented by the various centralized sound systems can be subdivided into two approaches. First and quite common are systems that I will call cellular or zonal in the way they cover the audience. Zonal coverage refers to forming a cluster of directional speakers and dividing the audience area into many smaller zones or cells and then dedicating a speaker to providing sound for each particular cell. Each speaker box then can be EQ' ed and volume adjusted to provide proper sound for the humans in it's coverage pattern. With this type of system setup, the overlaps between the box to box coverage patterns is crucial and of much concern. The goal and challenge of the system designer and tech setting up the system is to achieve seamless sonic transitions between the cells, which is no easy task. Another challenge with a cellular coverage sound systems is attempting to adequately cover areas at extended distances.

The second concept of coverage I will refer to as summed or combined. Summed coverage is the attempt to get multiple speakers to add together and act as a single larger speaker. The coverage pattern of this giant speaker would then be adjusted to cover the room by varying the angles between the boxes much the same way as the cellular approach. The big challenge with the summed approach is getting perfect cooperation between the various speakers, typically by getting them the speakers close enough together in order to minimize them acting as separate sources. Sub woofer arrays are almost always implemented in a summed array.

The key difference between the two methods is that cellular approach is based on minimizing the overlap of coverage patterns and the summed approach relies on smoothly combining the outputs of multiple speakers so the act as single source. What well designed versions of both approaches try to avoid is having a listener hear two acoustically 'separate' sources that are in close proximity to each other that are also not equidistant from the listener. Why, you ask? Well, mainly because non-equidistant sound sources tend to sound bad and creates comb-filtering that reduces output levels and screws up the frequency response.

Sound, like everything else in life, is never black and white and exists only in varying levels of gray and the reality is that real world concert sound systems exhibit varying degrees of both approaches. The high frequencies naturally lean toward zonal coverage and the low frequencies inherently tend toward combined coverage. The techniques that sound system designers implement to push the various sound systems toward cellular or or summed coverage patterns is quite interesting and ultimately a key factor in the clarity and sonic consistency of the system created. Just for good measure, I will give a few examples of common systems and my perception of the design approach behind their creation. Nexo's Alpha system, ElectroVoice's X-Array and Turbosound's Flashlight and Aspect systems are all excellent examples of zonal systems. Much effort was put into those designs in order to achieve distinct and consistent vertical and horizontal coverage projected from each individual box. The building block for these zonal systems is usually a relatively few speakers in each box that are mounted on some sort of horn to assist with pattern control. The boxes are then aimed to optimizes covering the accoustic space while minimizing sonic overlaps.

The summed-output system approach, until recently was considerably less wide spread with the Clair Bros S-4 system, the Rat Trap 5 and to some degree perhaps the Showco Prism systems being recognizable examples* . These systems tended to rely on boxes with quite a few speakers in each box that are in relatively close proximity to each other allowing them to unify their outputs and allow multiple boxes to begin to act as a single giant speaker. These sytems inherently by design have overlapping coverage from multiple drivers even within each individulal box. An issue with these systems is created by the physical spaces between the speakers themselves that cause the components to act like multiple sources creating box to box overlaps and comb filtering and inconsistencies in coverage patterns.

Pic of Rat Trap 5, Pic of Prism

Then in the mid 90's along comes theV-Dosc line array, a fully summed-output approach sound system that for the first time on a major scale, incorporated the high frequency component in the summing. Line arrays are not new, the old Shure Vocal master with a stack of 10" speakers inside is a old example. Take a close look at a Clair S-4 and you can see that the 18"s and 10"s form vertical line arrays when stacked and check out the Grateful Dead's Wall of Sound which had vertical line arrays for nearly every instrument.

Pic of S-4, Pic of Vocal Master, Pic of Wall of Sound

So getting back to the original question of "Are line arrays truly better and here to stay or just the latest fad?" Let's take a look at couple of things that make line arrays an interesting and useful implementation of the summed approach. Though I have heard it described different ways and even read various manufactures' press releases arguing about 'who describes it correctly,' for all practical purposes they are all saying that a well designed line array system offers improved volume level consistency vs distance when compared to a zonal type coverage system. Now whether you prefer to envision it in the 'cylindrical waveform' description offered by the folks at L'Acoustics or you just think of it of "as you get farther away the sound naturally gets quieter but since there are a higher quantity of equidistant speakers pointed at you so the volume drop with distance is somewhat counteracted." The fact that a line array system can be set up to project sound over short or long distances merely by altering the angles between the boxes is quite useful.

Another feature that the slender line array systems offer is that their narrow profile is quite easily intermingled with the exceedingly popular video walls. People want to see what people want to see and it tends not to be the sound system, except for a few of us, and having the ability to slide a large scale system into the small gap between a few video walls or set pieces is a strong asset. Plus, the relatively simple two dimensional rigging that only deals with vertical adjustments not only allows for a high degree of predictability, it also is fairly easy to get motor points for hanging in most venues. The fact that line arrays are simple, practical and predictable gives them a real world implementation advantage over systems the require multiple precisely spaced motor points to provide proper venue coverage.

But you know what, even with all those useful and apparent assets, none of them truly give line arrays a hands down advantage. Zonal systems can deal with volume consistency over distance by implementing long throw boxes and utilizing volume shading to compensate and project louder sound to the far away areas. Compact high volume zonal systems can be incorporated into well thought out set designs and even be flown behind new modern video walls that allow sound to pass through. Well designed rigging systems that allow zonal PA's to be flown and rotated and adjusted are and perhaps someday even by remote control, either in existence or not far off. Finally, sonic prediction software is not unique to line arrays and the realty is that the playing field is fairly even from a technical standpoint, except for one thing and it has nothing to do with the sound system or it the cleverness of its designer.

The thing is us. We are humans and like many critters that run around this planet here we have ears and also like many critters, our ears are on the sides of head. The physical and biological placement of our hearing devices allows us an extremely astute and accurate ability to discern the precise horizontal positioning of sound sources and the approximate vertical positioning of sound sources. Does it not make sense that a two legged walker of a human would require an increased sensitivity in auditory perception in the horizontal plane where most of the food to hunt for and predators hunting us would exist? Even our necks are designed with a limited vertical range of motion and a much wider horizontal rotation and at any given moment we are turing our heads or bodies sweeping the horizontal auditory plane. We enjoy things in stereo, we place the stereo speakers spaced apart horizontally to maximize the effect, have you ever seen heard or wondered why stereo speakers are not placed vertically? In some apartments and houses it would sure make sense logistically. Have you ever tried to stack a line array on it's side? It is quite interesting as it typically does not sound very good. For those of you pondering in your mind about L'Acoustics ARC's, Kudo's and other manufacturers horizonatlly arrayable products, take a close look and you will find that there are strict angles between boxes when horizontally arrayed that minimizes overlaps in HF coverage and they are set to merge the coverage paterns. Hey, wait a minute, isn't that a zonal system? Exactly, and for many applications zonal systems are optimum but when you need to focus a tremendous amount of sonic energy in a particular direction, there are distinct advantages to forming a giant and controllable unified sound source vs a cluster of tiny separate and directional sound sources.

So here is the deal as I see it. With current loud speaker technology it is necessary to utilize multiple speakers in order to cover a large venues, as no one makes a single loud speaker that is loud enough, sounds great and is versatile enough to cover 10's of thousands of people in a wide range of venues. These multiple speakers need to be arranged in some sort of configuration vertically, horizontally, both or maybe someday one behind the other. Currently, we can get speakers to sum together quite well but not perfectly. Our ears are very sensitive to those imperfections in the horizontal domain and our ears are considerably less sensitive to those same imperfections in the vertical domain. Therefore, the true design advantage that line array's posses is that they take advantage of the human deficiencies in vertical hearing by keeping their imperfection in the plane where we are least likely to perceive them and provide little or no component to component imperfections where our hearing is most sensitive. In other words, it is all about offering the human listening ear a single source in the horizontal domain which a line array does by design and a horizontally slpyed zonal system struggles to achieve. Combine that with the fact that they hang nicely like a string of beads and I will venture to say that line arrays may just be a bit more than the latest fad and more likely a structural building block to the sonic future of large scale sound systems.

  • The actual components and configuration of Showco's Prism system is kept 'secret,' so it is my opinion based on mixing on the system and it's sonic characteristics that lead me to believe that it is based on a summed-output type design.
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