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Arrays with more than 3 pipes.

Posted by David Aiken (A) on June 9, 2004 at 14:20:59

In Reply to: Re: Why indeed! posted by Sampsa on June 9, 2004 at 12:37:58:

If you try something along the lines of my quadratic residue or primitive root layouts, the width of the array is simply the width of a single pipe multiplied by the number of pipes you use. There are gaps in the array, but they result because the pipes are staggered in depth rather than in width, and the width of the gap varies from gap to gap because the variations in depth aren't all uniform.

As far as space goes, the problem becomes the depth of the unit. If you don't have much space behind your Maggies, you probably wouldn't fit a unit in. The smallest quadratic root layout I have a formula for is for 6 pipes with a depth equivalent to 5 pipes, plus a bit extra for the base of the unit to provide some support. Using my spacings, an 8 pipe unit has a depth of 5 pipes and an 11 pipe unit has a depth of 10 pipes - basically depth will be 1 pipe width narrower than width. The quadratic units will have a symmetrical diffusion pattern.

The Primitive Root units will have the same depth as width, but a slightly different number of pipes and they have an asymmetric diffusion pattern. If you were going to use them, you'd want to build mirror image pairs and you could then experiment whether you got better results with scatter to the outside of each Maggie or to the centre.

You can reduce the depth of both sorts of units by reducing the depth spacings for each pipe. You could halve the depth, for example, by using depth intervals of half a pipe diameter instead of the full pipe diameter I used. This will narrow all of the gaps by a bit more than half so the lowest frequency for effective difraction will drop. You could drop the depth even further, but you're going to lose effectiveness as you do so because you're closing the gaps up. I haven't tried any depth interval other than the one I'm using, but if I was going to I wouldn't reduce it to less than half a pipe diameter for that reason. I also probably wouldn't try increasing it beyond a full pipe diameter because I think the gap widths might become too wide.

You can also use the standard pipe side by side layout and keep adding pipes if depth is an issue. There's no limit to the number of pipes you could add this way. There are 2 different gap widths in the standard 3 pipe array and I'd just keep alternating those 2 widths. There's no reason not to build an array the full width of a Maggie if you wanted to, and you could place it so that it was completely obscured by the Maggie so it simply was 'invisible' most of the time. The only problem with increasing width is going to be that you'll want to increase the base depth a bit for stability. You could do this simply by extending the support points front and back with legs that extended out from the standard depth base.

David Aiken

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