Wednesday, 23 April 2014

Line Array


Yup, behold and wonder finally, after the whole pro-audio world is all ready (ab-)using them for years in all kind of matters I finally also start yabbering about them:

Line Array's


Or actually  curve linear arrays or whatever you like to call these boxes on a string..
There has been enough talks about the 'working' of these and actually, there is not much to say since mr Harry Olson did his thingie all ready in 1957 or so.
The one model that is definitely not going to work for me is the pie shaped dispersion nonsense.
So clearly we need a string of small loudspeakers in a very close spacing relatively to the frequencies they have to reproduce.
And furthermore a total array length of say at least 2.5 mtr to do anything at the, for us metal heads , so beloved low-mid frequencies.
That will give us the combination of one 12' and two 6' speakers in a cabinet of 35cm high. Which gives us a array length of more then 2 mtr with 6 units.
Not a big problem, and our FIR filter skills will prevent the comb-filtering in the horizontal plane.

But then it is 2014 so we apparently also need some high end..
Well lets start of with making a 'waveguide' (duhh) for these:


Tada..the first experiment.
A bit difficult to do large scale measurements in a shed from 4 x 5 meters so we will have to resort to some brain action:

 Let 's assume we have a straight array of 2.5 high, suspended from the ceiling with the lowest cabinet at ear height. (totally wrong I know, I know)
At long distance the waves from every unit in our will arrive at more or less the same  times.
If we approach the array to a  distance X, the path length between the highest and lowest unit in the array will start to introduce cancellation.
Take 3440 hz as a crucial frequency, so with 0.05mtr path length difference this will yield to a full cancellation.
Calculate..calculate.. any closer then 62mtr this will give grieve!!
Now pull back and tilt the whole array for b cm.
With b = 10 cm you can move up to 20mtr, and with b = 20 cm up to 12mtr
Conclusion: All ways tilt your array!

(there is a caveat though!, soon more to follow)