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Predicting Array Performance: Hanging The PA Right The First Time
Taking the guesswork out of seeing where your sound is going
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Almost all of the reputable manufacturers have basic cabinet data available on their web sites and product CDs. This allows the system designer to pick and choose different cabinets for different applications, mix manufacturers or even, in the case of some of the big dogs, generate EASE data for their proprietary boxes.

We can use this data to predict coverage and SPL levels in a room, set delay times and volume levels of specific cabinets and even to model complex interactions between devices. EASE also does acoustical predictions including reverb time and intelligibility estimates.

For the audio consultant who has time to painstakingly draw a room and insert all of the appropriate wall and ceiling treatments, this is a great tool. But does this really apply to the touring community?

The line array craze has managed to drag some of us kicking and screaming into the world of predictive software. Line arrays only behave like line arrays are supposed to behave when the cabinets interact properly. The “hang and bang” approach leads to extremely uneven results in the real world. So, almost all of the manufacturers fielding these products have created some software to assist their users.

These are not true modeling packages because, with a few exceptions, they only help you determine vertical splay angles needed to cover angled floors, balconies and the like. The horizontal coverage of most line arrays is a fixed quantity. And level prediction with a line array is frequency dependent in the far field.

The point at which we go from the vaunted 3 dB loss per doubling of distance to typical inverse square law behavior (6 dB loss per doubling of distance) changes with frequency, making broadband SPL predictions difficult. But for most of us using traditional cabinets in traditional clusters, there are some very useful tools out there for making sure we hang what we need to hang and point it where it needs to point.

A program I have employed with success is LARA from Integral Acoustics. It uses EASE data, so most commercially made boxes can be imported. It has a convenient library of pre-constructed rooms that correspond to most of the typical venues we encounter.

They are easily modified to reflect the exact dimensions of a particular space. Defining acoustical treatments is not necessary because LARA treats all surfaces as a perfect absorber. In other words, we are only modeling direct field coverage and not trying to predict how the sound system and the room will interact, so the time required to build a room is reduced to a minimum for the well-prepared house engineer many of the venues have floor plans available on the web.

For those that don’t, getting room dimensions can become part of advancing the show. But even if none of the information is available in advance, this program is so quick that a room can be modeled on site while the truck is being unloaded.

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