(this is a great article on line array rigging safety...worth the read)...
Some in audio think that the term “rigging” only applies when loudspeakers are flown, but it also pertains to lesser endeavors such as placing a single loudspeaker on a tripod stand. The bottom line is that for any piece of production gear not sitting directly on the ground, steps must be in place to insure that it does not fall and injure someone (or worse).
The Occupational Safety and Health Administration (OSHA), the U.S. agency that sets and enforces work safety standards, states a company must have “competent” and “qualified” persons in charge of rigging. A competent person is described as one who is capable of identifying existing and predictable hazards in the surroundings, which are dangerous to employees and has authority to take prompt corrective measures to eliminate them.
Meanwhile, a qualified person is defined as one who by possession of a recognized degree, certificate or by extensive knowledge, training and experience, has successfully demonstrated the ability to solve problems relating to the subject matter and the project. Therefore, a qualified person designs a rigging system, and a competent person installs and monitors the rig, and inspects its components.
While OSHA rules and standards are mainly focused toward rigging in the construction industry and are geared toward safety of employees, we also need to look after the safety of performers and members of the public who attend events. Not everyone at a gig may be at the level of a qualified or competent person, but all should focused on safety. Anyone on a production crew who sees a problem with rigging (or any other safety issue, for that matter) can call “stop” and point out the issue so it can be addressed and corrected to avoid an accident or injury.
Good places to look for training and information are manufacturers who make rigging equipment or loudspeakers that fly. They provide specific safety and operating instructions for their own gear. Two organizations focused on entertainment rigging training are the ESTA Foundation (estafoundation.org) and PLASA, which offers the ETCP rigging certification program (etcp.plasa.org) for entertainment riggers who work in theaters or arenas.
There are also several independent rigging schools and manufacturers that offer training and certification programs as well. A good reference book is Entertainment Rigging by Harry Donovan. While reading about proper rigging practices is highly recommended, it’s not the same as getting hands-on training. Experience along with knowledge is required for a person to be designated as competent.
Before we talking about specific rigging approaches, let’s look at a few terms. Initials often seen on stands and rigging equipment are “WLL” (Working Load Limit), “SWL” (Safe Working Load), or “MRL” (Maximum Rated Load). For practical purposes, they mean basically the same thing: the maximum amount of static weight that the item will safely hold continuously, when it is used correctly as intended. The key here is a static load, or a load that does not move. Any movement like loudspeakers swinging in the wind or even the act of raising or lowering a chain motor puts additional stresses on rigging equipment. Safe working load limits should never be exceeded.
Another term to be familiar with is “Safety Factor,” the margin of safety added to an item that takes into account loadings over and above the weight being hoisted and for reductions in capacity due to the extra loads imposed by acceleration and inertia (movement).
Some European countries have mandated 10:1 safety margins, while those in the U.S. are still largely self-enforced. Many production companies in the U.S. have adopted a 7:1 safety factor, with margins for life safety (fall arrest, performer aerial acts, etc.) using a 10:1 ratio.
In short, an item’s safe working load is derived by dividing the breaking strength (the point of failure) by the safety factor. An example would be a shackle with a breaking strength of 7 tons would have a safe working load of 1 ton here in the U.S. (SWL= Breaking Strength (7 tons)/safety factor (7:1).
System design plays a large part in the rating of individual components. Like a chain, a rigging system is only as strong as its weakest link. Pull angles and side loadings de-rate the SWL of many items including eye bolts and shackles.
The splay angle of bridles (two or more legs of wire attached to a ring that spreads the load across a larger area) affects their weight loading. Spansets and wire rope slings will have different capacities based on their positioning (i.e., straight vertical pull versus a basket configuration).
All of these factors need to be taken into account by a qualified person who will design the rigging system.
In addition, a competent person should inspect all rigging equipment and hardware before use and periodically do a major inspection for signs of wear, abuse and general adequacy, as well as perform any manufacturer recommended preventive maintenance.
Follow the rules and don’t cut corners when it comes to rigging. Use only loudspeaker cabinets designed by the manufacturer to fly, and use only hardware approved for that specific model. Follow all manufacturer recommendations concerning their individual products. Never modify any rigging hardware as it may affect the weight loading capacity of the item. Purchase only known quality rigging equipment.
Further, factor in enough time to do rigging correctly and make sure the crew isn’t tired—rushing and fatigue cause accidents. Double check everything before it goes up in the air. Once items leave the ground, they better be rigged properly or gravity will demonstrate why it’s the most powerful force in the universe!
Only finger tighten shackle bolts, never use a tool. If you’re worried that a pin might vibrate out, mouse (secure) the pin in place with twine or wire. Always load a shackle pin to end, never from side to side. When attaching to a beam or other structural component, always pad the beam edges so a sharp edge doesn’t injure the wire rope or sling. Never leave any slack in guy wires.
Plenty Of Methods
Now let’s move on to looking at ways loudspeakers can be deployed and positioned.
Keep in mind, however, that strapped stacks can be top heavy and can topple over, either from vibrations or from a crowd pushing to get closer to the stage. Using a larger subwoofer that provides a bigger footprint as the base of a stack can add stability to a strapped stack of loudspeakers.
Many line arrays are designed to be ground stacked by inverting the fly bar and using it as a base. The cabinets are connected to each other and the base with their fly hardware, making a stable ground stack with the angles being able to be adjusted for coverage same as when flown. Loudspeakers placed on uneven terrain will be unstable and if used on a grass or dirt surface could shift during rain. A common remedy is to place a stage or plywood platform on the ground and level it. Then the loudspeaker stack will have a solid level surface to rest upon and not sink into mud after a rain storm.
Scaffolding. Before flying PA was common practice, stacking loudspeaker boxes on scaffolding towers was a common approach at larger shows. It’s still a common way of elevating horizontal arrays and delay stacks at festivals and fairs. On uneven ground, screw jack leveling legs should be used to ensure the scaffolding is level and all cross and diagonal bracing needs to be in place before loading the tower. Make sure all decking is securely in place before any speakers placed on the tower and they should be strapped down so they can’t vibrate off.
If used outdoors, the tower needs to be guyed down in case of winds. Signage and banners placed on the scaffolding act like sails and will transmit high wind loading to the system. Using an open weave fabric for the signage will allow some wind the blow through, reducing the wind loading on the tower.
Stands. Tripod stands are commonly employed for loudspeakers at smaller shows. While very safe, the tripod legs should be extended to their largest footprint when possible so they provide maximum stability for the stand. Make sure the top of the stand is correctly sized for the loudspeaker socket or the cabinet could tilt and its center of gravity will not be directly over the pole.
Also, position the stand where the tripod legs will not be a trip hazard as a fall could cause a person injury, as well as possibly knock over the stand (and loudspeaker).
Use fixed leg tripod stands only on level ground. Saddle style sandbags can be used with tripod stands to add a bit of weight to the bottom for increased stability. The sandbag should straddle the leg, not hang from any bracing. To avoid crew injury, larger loudspeakers should be hoisted onto stands by two people.
Truss Totem. Particularly popular on corporate gigs, truss sections are bolted to bases and used in an upright position for lighting trees, projector and delay speaker stands. Totems can be very top heavy so additional weight, usually sandbags, are placed on the base to help with stability.
When used with a single loudspeaker on the top, make sure that the cabinet’s center of gravity is located directly over the center of the truss. When used with a column-type loudspeaker attached to the side of the truss, make sure that additional weight is placed on the base on the opposite side to offset any leaning tendency caused by the side loading of the loudspeaker. Totems should only be used on level ground. If used outdoors, these systems need to be guyed down.
Pole Mounted On Sub. Pole mounting a loudspeaker on a subwoofer provides a clean and easy setup for many gigs. It allows the top cabinet to be raised to a good operating height while eliminating the tripod base that may become a trip hazard. Some systems allow for the use of two poles for larger top cabinets or line array-style boxes. To avoid problems, use only the manufacturer’s recommended poles with these systems, as different poles may not be compatible or as stable as the factory units.
Crank Towers. These come in many forms from larger versions of tripods to heavy-duty units that can hold 600-plus pounds. Crank towers are becoming a popular option to fly a smaller array without having to use motors. Make sure that all outriggers and legs are extended and the tower is leveled correctly before raising the load. Factor in the rigging hardware weight and speaker cable weight when figuring out the total weight you will be lifting. Check with the manufacturer before using the lift outdoors and follow their recommendations on using the system outside.
Pair Of Towers & Truss. This is a common setup at medium-sized shows and corporates that utilizes a pair of crank towers and a span of truss that goes across the front of the stage. The truss usually does double duty and supports some front stage wash lights as well as the loudspeakers. It can give the ability to provide a small left, center and right array without requiring any ceiling points.
Care should be taken to not overload the systems, because total working load on horizontal truss is based on an evenly distributed load. Also take into consideration the weight of the loudspeaker and lighting cables when figuring out the total weight of the system. This type of setup is considered a system and needs to be designed by a qualified rigger.
Line Array Tower Truss. A relatively new option for positioning loudspeakers is the line array tower. Made from truss sections and specialty hardware fittings, these systems can be disassembled for transport or storage and easily bolted together on the job site to support a wide variety of speaker arrays.
Smaller towers may use a manual hoist to lift the array, while larger units utilize a powered hoist. Make sure the tower is leveled correctly before use. When deployed outdoors, the tower must be guyed down per the manufacturer’s recommendation. Some tower systems allow placing subwoofers on top of the forward outrigger legs so they can act as additional ballast.
Dead Hang Flown. Dead hang means that an item is connected to a support structure without a motor or lift system. The attachment point can be an exposed ceiling beam, tent pole, section of truss, etc. An engineer should be called in to certify the weight loading ability of any ceiling point before use if it is not known.
Only competent or qualified riggers should dead hang cabinets as each hanging point needs to be individually assessed by a person with knowledge and experience to determine what hardware is required to safely support and position the loudspeakers.
Access to dead hang points may involve a personnel lift. Make sure fall protection systems are used by anybody in the lift and that the systems are inspected before use. A spotter may be required to assist the lift operator as many types of equipment have blind spots.
Air Wall Tracks. Air walls are the moveable walls in large meeting spaces and ballrooms. These tracks are often utilized as ceiling points for video screens, lighting and audio delay speakers when they are not being used by the wall sections. While technically considered a dead hang, air walls pose a few specific challenges to production crews. All air walls are not the same, and each requires specific fittings dedicated for that track style.
There are also a few universal type air wall hangers that will fit a wide variety of common track styles—but they don’t fit all. Be sure to use the correct fitting or hanger for the track because some models may seem to fit into the wrong tracks, but they’re not providing the correct support. Air walls have limited weight bearing capacity per point, so it’s critical not to overload any point on the track. Because of their limited single point capacities, air walls are commonly limited to flying lightweight objects, or used as cable supports.
A building’s engineering department should be able to tell you how much weight and at what intervals you can fly from the track. One important thing to consider is whether the room needs to be reconfigured and the walls moved during or immediately after the event. If the walls need the tracks, nothing else can be installed on them.
Motors. They can be used singly to hoist individual loudspeakers and small arrays, and in multiples to hoist larger arrays. A motor attached to the rear of an array can be used to help tilt and aim the array. Only competent or qualified persons should perform any rigging with motors.
Before use, check the motor hooks and inspect the chain for any signs of damage. Make sure the chain bag is attached correctly and is in good shape. Before any motor is operated, the rigger needs to make sure that everybody on the deck is aware that something will be moving. Before an array or truss is lifted, one competent person should double check all rigging hardware and fittings.
Construction Lifts. They’re sometimes used to elevate or fly loudspeakers at festivals. Scissor lifts are popular when small horizontal arrays need to be raised, moved or relocated at events like airshows. Larger festivals might utilize construction cranes or large extendable boom forklifts to fly the main PA system.
Make sure the equipment operators are certified on that model unit, and that an operator is monitoring the equipment continuously during use. Weight loading changes depending on the angle of the boom so it’s vital to no overload the equipment during use. Tag lines should be used to keep an array from swinging in the wind. An engineer should determine the maximum wind speeds the systems can operate in, and if the wind reaches that limit, the PA should be lowered immediately to the ground.
Remember, safety is the most important thing. Rigging is dangerous, but using the proper equipment and procedures, skilled people can overcome gravity, one loudspeaker at a time.
In addition to being the owner of Las Vegas-based production company Tech Works, Craig Leerman is also a U.S. Navy trained and certified rigger.