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Technologies > The RSLA System
Allan So RSLA Systems in Mid-Sized Churches

Article by Allan Sohl

Allan Sohl has been with PAS for almost 25 years and is credited with developing Time Offset Correction™ as well as designing PAS speaker systems.


Arrays which take advantage of the smooth off-axis character of RSLA cabinets can be very effective.

Fig. 1. A simple rendering of a fan shaped 1200 seat church
In large RS-2.2 systems, putting 10° or less between cabinets requires rotating the coaxial horn 90° in order to reduce interference between cabinets (see article: “The RSLA System”). When these systems are rotated into vertical arrays, the horizontal coverage across the rated 60° included angle becomes very consistent with frequency. This lead PAS to develop a system of brackets, plates and ball-lock pins that make possible large vertical arrays that perform very well as line arrays.

This does not necessitate the use of large numbers of cabinets when only a few are needed.

For example, in a 1200 seat church where 25% of the seats are in a balcony, one of the requirements was that the space between the pews and the stage have intelligible sound. Like many churches today, it is a 90° fan shape. The front of the stage is an arc with it’s center at the point where the walls would converge if they were extended past the rear wall of the stage. The ends of this arc meet the walls at the sides of the stage about halfway between the outside of the proscenium and the sides of the hall. There is a lighting gallery above the second row of seating where the ceiling makes a step down about three feet before continuing to the back wall above the balcony. Figure 2 shows the plan view from the EASE model used in this simulation.

Fig. 2. The plan view of this church
For the purpose of this simulation, three sets of two RSLA cabinets are suspended above the height of the proscenium at the front of the stage (about 20 feet above the main floor). Though this means that they may obscure lighting, there is the consideration that a person seated the last row of seats on the floor has line of sight to the speaker cabinets.There will be some diffraction from the edge of the balcony. If this is a problem, it can reduced or eliminated by raising the main cabinets and adding small delayed cabinets under the balcony.
Fig. 3. Rendering using the center two cabinets at 4 kHz.
How well do these cabinets control the Mids and Highs?

Figure 3 is a rendering of this room from EASE showing the direct sound at 4 kHz from the center two RSLA cabinets. Figures 4, 5, 6 and 7 compare the response of the center set of cabinets with the response of all three sets of cabinets. Comparing figures 4 and 6 we can see that the coverage at these two frequencies is remarkably similar. Although this is due to the rising on-axis response of the 15 inch low frequency section of the coaxial driver, theincreased directivity that this causes results in more constant coverage with frequency than would be expected from this type of system.
Fig. 4, Center two cabinets, 4 kHz Fig. 5, All cabinets, 4 kHz
Fig. 6, Center two cabinets, 500 Hz Fig. 7, All cabinets, 500 Hz.
Figures 5 and 7 show that this advantage continues when the remaining two sets of cabinets are added.

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