Building the arrays

Designing DIY line arrays

My ideal shopping list for speakers contained the following list:

  • Dynamic speakers with above average sensitivity
  • Smallest footprint possible
  • No crossovers in the vocal range
  • Placing near (back)wall

Line arrays, consisting of full range drivers, were the only speakers I could find that ticked all those boxes. They even added some of their own features to that list. Due to being a line source they only drop 3 dB for each doubling of distances compared to 6 dB for more traditional point source speakers. If you choose a line array that covers most of the distance from floor to ceiling you also have the advantage of less problems with reflections from the floor and ceiling. The reflections from the floor and ceiling virtually add to the length of the array, making it seem even taller than it is.

Ideal?

Are DIY line arrays the ideal speakers?  If you read the above you’d certainly think so. A lot of debate is about the need for EQ with these kind of arrays. An array consisting of full range drivers will loose the line effect at higher frequencies. The speakers cannot be mounted close enough for them to add to each other. Basically they start to interfere with each other. The loss of energy is due to comb filtering in the higher frequency range. But by equalizing the higher frequencies of a full range array one can compensate somewhat for that loss of energy in the higher frequencies. That’s what makes this design worthwhile.

The lower frequencies also need help from equalizing. Due to the small size of the used drivers, 3.5″ tall, they will roll off a lot earlier than you want them to. But because there are 25 of them you have enough potential to equalize that low end. The total surface area of the 25 drivers exceeds the surface area of a 15″ woofer.

3D Design

So, time to fire up my favorite 3D design program to get a feel for what I could create (lucky enough to have a license at work). There were some basic ideas in my head that I wanted to incorporate. I had seen translam constructions that appealed to me. A stacked construction that would enable me to create a round outer shape for the DIY line arrays to counter diffraction and a irregular shape on the inside to combat the back wave from the speakers. No parallel walls anywhere, all small details to help get better sound potential.

Inner design of the DIY line arrays

Here’s the design shape I ended up with after some earlier tries that didn’t seem quite right to me. You can see the rounded outside, almost an ellipse shape and the inner irregular shaped chamber.

Another benefit from the wavy shaped interior is the varying wall thickness of the enclosure. It is no longer a straight flat surface. The wall thickness varies from 18 mm minimum to about 30 mm.

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