Line arrays and inter-element angles.

[Phil Graham]

Re: Line arrays and inter-element angles.

If we had to accept a level gradient down to our low frequency we would never do better than 6dB per doubling of distance.

In the far field, arbitrarily far away from even a large array, assuming it is in free space, you end up with point source behavior for any box/array. Nearer the array, and for frequencies where the array is large, we see "less" than the point source behavior. This is due to incoherent summation, which reduces the level relative to what one might see from a point source. The net result is more evenness, but the overall levels near the front are reduced relative to the pure point source case. We aren't currently "beating" point source propagation, we are just slowing the volume increase as we get closer to the array, for an overall improvement in evenness.

In rooms, the reverberant field will slow down the decay vs. distance, but once you get out near the critical distance where the direct sound and reverberant field levels are comparable, the perceived sound becomes pretty marginalized quickly.

 

[Brandon G Romanowski]

Re: Line arrays and inter-element angles.

"In the far field, arbitrarily far away from even a large array, assuming it is in free space, you end up with point source behavior for any box/array."

Right... but since our audience is specifically a distance away we manipulate the array to create some wideband even SPL and not necessarily consistent tone. If you were 300' from an array you would expect the HF to fall off... and if you were 3' from a subwoofer you would expect to hear a great deal of low end, but in both locations there should be some broad frequency range that is fairly flat and consistent in terms of SPL. Array calculators not withstanding, nobody wants to hear erratic frequency responses but I do not think that it is a simple case of choosing even tone over even SPL.

 

[mackerr]

Re: Line arrays and inter-element angles.

I do not think that it is a simple case of choosing even tone over even SPL.

It is not an either/or, but it is a tradeoff. Optimizing for even SPL near to far will come at a cost of even frequency response near to far. It is up to the designer/tech to decide which to favor, and by how much.

The Martin MLA design software has sliders to give levels of importance to even SPL, even frequency response, and temp/humidity for HF loss.

Mac