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30 Driver CBT Line array 30 Fountek FE87 driversper array
30 Driver CBT Line array 30 Fountek FE87 driversper array
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Old 12th November 2015, 05:42 PM   #1
T85matt is offline T85matt  United States
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Default 30 Driver CBT Line array 30 Fountek FE87 driversper array

I am just getting started on building a CBT. this will be my first big build. I am going to be doing shading using series and parallel connections and I will share my wiring diagram on here shortly. feel free to use it. My only question is more a matter of design of the array of speakers themselves. I am wanting to run two rows of 15 speakers for the array should i run them simply side by side or would there be any benefit to running them staggered?



Last edited by T85matt; 12th November 2015 at 06:13 PM.
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Old 23rd November 2015, 07:54 AM   #2
aoc is offline aoc  Malaysia
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I'm planning to build a 8 a side array, looking forward to your progress
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Old 12th April 2016, 03:06 AM   #3
dynomike is offline dynomike  Canada
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Did you ever get around to building this? The idea of using series parallel for shading is interesting, if it could be made to work as intended (by mr. keele)

I would strongly recommend *not* doubling up the rows and especially not staggering them. That will mess up the horizontal dispersion.

I'm also interested in these drivers for line arrays, so please update us on your progress!
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Old 26th December 2016, 06:51 PM   #4
Patrick Bateman is offline Patrick Bateman  United States
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Dave Smith has done a lot of work on arrays. He posts here as "speakerdave." Mr Smith has worked on arrays from Snell and McIntosh, and worked on projects at JBL. I believe he worked alongside with the CBT inventor (Keele) at JBL.

Mr Smith has posted good results when using 'log shaded arrays.'

Log shaded arrays and CBT arrays are not the same thing, but it's occurred to me that it should be possible to combine them.

Here's how this works. This is a 'laymans interpretation', so Mr Smith or Mr Keele might correct me here.

Having said that, here goes:

In a CBT array, we are improving the off-axis response by manipulating the amplitude and the phase of the array. You can manipulate the amplitude by lowering the voltage passively, using resistors. Or you can manipulate the amplitude by using dedicated amplifier channels. We are manipulating the phase of the array by curving the array. You could accomplish the same thing via DSP delay, or even passive delay. The patentholder of the CBT technology does both, depending on the model. (IE, they have some CBT arrays that are physically flat but electronically curved.

OK, I hope that made sense. I've posted about CBTs over the years, and the concepts described above are related in greater depth in some of my older posts.

Now let's talk log shading.

As I understand it, log shading reduces the amplitude of the array at the edges. The exact same thing that a CBT array does, and many other shaded arrays. The 'neat' thing about the log shaded array is that the shading is accomplished by simply eliminating elements in the array. For instance, if you had a sixteen element straight array, you could 'shade' the array using resistors. Log shading 'shades' the same array by simply omitting elements. IE, if you want half as much power going to the edges of your array, instead of reducing the voltage to the edges by half, you can simply omit half of the drivers at the edge of a log shaded array.

That paragraph above is a simplification of how log-shading works. For all the detail, you can get the math in the patents. But IMHO, the idea is the same. If you want to shade an array, you can simply eliminate elements of the array. This has quite a few advantages, particularly in consumer audio:

1) It requires fewer drivers
2) For a given number of drivers, you can get directivity control lower. For instance, if you have eight drivers and a center-to-center spacing of 5cm, your line array will have directivity control down to 850Hz. If you use log shading, and you stretch the length of the array by 50%, you'll be able to control directivity down to 567Hz with the same number of drivers. (40cm array vs 60cm array)
3) Assuming that you're using the same voltage to every element in the array, you don't have a 'single point of failure.' In a CBT array, the drivers at the edge of the array are receiving a tiny fraction of the voltage going to the center. Due to this, the elements in the center of the array are 'the weakest link' in the chain.
4) resistor arrays are expensive and bulky. Log shaded arrays don't need them.
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