Audio Landmines:
Using Portable Sound Systems
in Unfamiliar Situations
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| by Tom Young |
No where in the world of live sound do more potential landmines exist than in “one-offs”, those events that are basically “hit and run.” These events seldom come with sufficient time for load-in or thorough sound checks. But these are the events that build character, test our resolve and have the potential to help shape the aspiring live sound person’s career and/or expertise. Such events provide a wonderful opportunity to explore electroacoustics and to learn the human limits of dealing with God’s Laws of Physics. These events can also provide numerous “teachable moments” about stagecraft, diplomacy, and compromise.
Loudspeaker coverage and location are of paramount concern, in part because, unlike an installed sound system, we have some control over where the loudspeakers are placed. Basic rules-of-thumb is to elevate the loudspeakers as much as is possible, set them up in a secure and safe manner and ensure that they are closer to the audience than the front line of microphones on the platform or stage. Before you buy or rent portable loudspeakers for these temporary events, carefully consider the required sound coverage patterns. In most smaller events, you probably will not be suspending (flying) your loudspeakers. So we will assume that you are dealing with two loudspeaker positions (left and right) and that these are run in either mono or stereo. If you have only one loudspeaker per position, you should probably use a wide horizontal by narrow vertical coverage system, such as 90° x 40°, so that you have sufficient combined horizontal coverage. If you are able to have two loudspeakers per position, then it is appropriate to use devices with narrower horizontal coverage so that they may be “arrayed” to some degree. The term “array” has become as much a marketing term (often grossly misused/exaggerated) as an engineering term, but it means simply to place or splay one loudspeaker next to another so that the coverage angles line up in an attempt to minimize overlap. The alternative to properly arraying loudspeakers is to haphazardly set them up or purposely overlap their coverage patterns. This alternative can yield higher acoustic output, but at the expense of system’s linearity, or the smoothness of the system’s frequency and phase response. In this world of “one-off” events using portable sound systems, we may choose to go in either direction. However, the priorities guiding such decisions should always include making sure the entire audience is covered, and secondly, attempting to achieve smooth response.
Once we have chosen loudspeaker positions, we need to be conscious of where the band or the presenters decide to stand on stage. A microphone’s proximity to the loudspeakers can determine its susceptibility to feedback. Many loudspeakers, especially those that are candidates for stand mounting, have less directional control at mid and low frequencies. However, knowing and using that pattern control is an effective way to prevent feedback. Microphones that are located behind the loudspeakers, or placed far out of the rated coverage pattern, are less likely to feedback.
Each new location presents its own set of acoustics. However, if you are performing outside, away from walls and other obstructions, then you are blessed with having little or no acoustical problems with which to contend. You will spend much less time “fighting the room,” and effects, like digital reverb that add “desirable” acoustic elements, can be put to good use. With no walls to deal with, stage volume may be less of an issue too. The downside (and there always is at least one) is that your band and choir may find that the boundary-free environment prevents them from hearing one another very well. They will probably rely more on the monitor system than in an indoor environment.
If the monitor system is not adequate, or if it gets too loud, you may have a serious problem.
Another potential downside is that you will need more shear horsepower from your system in order to create the same levels that you would in an indoor environment.
If your one-off is inside then you are likely to have a 50-50 chance that it will be acoustically acceptable. If you can afford it, you can lessen the negative effects of an acoustically “challenging” space by investing in heavy theatrical drapes with rigging hardware to line the walls of the platform/stage and the back wall behind the audience. These drapes can be custom made by theatrical supply houses and should be made from fire-rated fabric. Placing such treatment directly against the reflecting surface is much less effective than hanging them several inches away from these surfaces. Up to 12 inches is not too much.
If you have the flexibility to locate the stage platform wherever you want, you have an added advantage in cutting down on negative acoustic issues. Putting the platform in a corner can cut down on slap-back echoes in a box-shaped space. In a long room it is usually better to be at one end than to be along a long wall and firing directly across. However, in a long room you are less likely to have enough sound pressure level (SPL) at the rear without a well-designed, flown loudspeaker system or one with delayed satellite positions located toward the rear of the room.
The FOH mix position should be located within the audience area away from walls or other obstacles. For one-off’s, it is often possible to get the mix position dead center in the room. But be very careful about the distance from the mix position to the loudspeakers. A comfortable volume level at the back of the room may be painfully loud for those in front. A general rule of thumb is to be halfway back in the room.
For safety sake, pay close attention to how and where the snake and AC power cables are run. You may consider burying these for certain outdoor events, but don’t go digging up the perfectly manicured baseball diamond! At the very least, ensure all cables are secured and clearly marked to minimize their potential as trip hazards. For indoor events, consider running the snake along the side, near the base of the wall. And running casters over cables is a sure recipe for damage.
AC power is often another unknown factor and can prove to be a big headache. Short of getting a professionally made AC power distribution system (aka: distro) that requires a licensed electrician to “tie” it into the building, you will be well served by getting heavy-duty, professional-grade AC cables with sturdy outlet boxes. These should be made with SJO or similar outdoor “portable duty” type cable jackets and, at the very least, 12AWG conductors for anything over 25 feet in length. The orange cables that are commonly available at hardware and department stores are seldom of sufficient quality. If possible, the entire sound system should be powered from the same AC power source or branch. A sound system that is powered from several sources stands a very good chance of being noisy or tripping circuit breakers. Do not get the stage power from one service and the FOH mix position power from another.
Make sure to run all the microphone, speaker and power cables, and perform a through system check before “dressing” them for appearance and safety concerns.
Invest in good quality microphone and speaker cables, and treat them well. Over-the-elbow cable wrapping is a sure path to short cable life. All cables have a natural self-coil tendency, or memory, and you need to ensure that when you tear down the system you carefully wrap or coil cables in a manner that does not force them against their desired direction. Whether indoors or outdoors, cables accumulate dirt and grime. Clean them periodically with warm water (a bit of very mild detergent is OK) and wipe them dry.
Lastly, no one should run sound without a helper. Even a completely untrained ‘gofer’ can be instructed to go backstage and observe amplifier indicators, listen to all loudspeakers to ensure nothing has been blown, watch the mix position while you go wash and confer with the others, or to get you a plate of food, etc.
We have just scratched the surface of what it takes to pull off a successful one-off using a portable sound system. Such events are extremely educational and often can be humbling, character-building experiences. Believe it or not, one day even the most horrific one-off will be recalled with fondness and even a longing to return. But it is most important to plan ahead, work hard and keep your eyes on the prize and have fun.
