Planning and Simulation of Public Address Systems

A sound system and the surrounding room are two inseparable components, which define the acoustic properties of a venue. This is why planning large PA systems is only possible in consideration of the room acoustics. Simulation software like EASE is a powerful tool, which allows a good prediction of acoustic properties of the system before it is installed.

Before planning the system itself, one should establish the technical criteria it has to meet. Depending on the application this can be the sound pressure level, which needs to be attained in a defined frequency interval, an especially linear transfer characteristic for high class music reproduction, a prescribed speech intelligibility for emergency warning or the immission control in the outside areas. Furthermore aspects like the protection of historic monuments, vandalism resistance or a specific optical design can become relevant.

Prerequisite for the simulation are high resolution balloon data of the loudspeakers including phase distribution in at least a 5° raster.

The simulation procedure starts by constructing the room, which the equipment is to be installed in. Here all the acoustically relevant elements have to be included, at the same time irrelevant details remain out of consideration, in order to keep the computing time within a limit. As precisely as possible, all the elements are now given parameters for absorption and scattering, which depend on the material used and its structure.

With this model already, the reverberation time according to Eyring or Sabine can be calculated. Comparing the result to reverberation measurements of the room allows readjusting in the model.

Now the loudspeakers are inserted into the model. In case line arrays are going to be used, tools for determining the basic configuration are useful. The objective is a constant coverage of all the audience areas, while avoiding highly reflective surfaces.

Next, the distribution of direct SPL is simulated. Even for a high resolution the computing time for this is rather short. The results in the audience areas as well as outside can be used to adjust the arrangement of the loudspeakers.

Afterwards the impulse responses at selected positions are simulated according to the mirror image source method, using the Aura module in EASE. From here, more parameters can be calculated, like the precise reverberation time with the model sources, total SPL and speech intelligibility.

Ultimately the auralization is generated by convolving arbitrary signals with the impulse responses, to allow an impression of the system's sound in the room.



Alfred Schmitz

Anselm Goertz