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A different layout for the pipes

Posted by David Aiken (A) on April 8, 2004 at 20:15:07

In Reply to: Jon Risch or others, question on Large room lens diy....... posted by Norman Bates on April 8, 2004 at 03:14:40:

Some months ago I posted on a different layout I had started using for a room lens made of 8 pipes. What I did was to place them according to a quadratic residue formula in the same way that well depths are staggered in a quadratic residue diffuser. I found that this worked better than 3 sets of normal 3 pipe units placed side by side in the same spot in my room.

From the front I have no gaps between the pipes. Side on, they are spaced at different depths according to a quadratic residue formula though the overall depth of the array is 4 pipe depths so you really don't see any gaps looking at the array from the side either, since all of the gaps are at angles to the front and side. Since the depth placement of the pipes does not proceed uniformly from front to back as one progresses from the side to the centre of the array, the width of the gaps varies from gap to gap from the side of the array to the centre, and the gaps on the left half are mirror images of the gaps on the right half of the array. I have kept the pipes parrallel in this configuration, not angling them slightly in relation to their neighbours as in Jon Risch's standard instructions. I haven't heard any problems from this in practice, though gap widths may well be relevant to this. And while I am quite happy with the results, I have to admit that there may well be an element of luck in that since I decided to see whether placing the pipes like the well depths in a QRD array worked

I haven't taken any measurements to try and quantify the results, and have no idea how to best achieve that anyway. I happily admit that my assessment that the results are better than 3 standard units side by side is simply my personal impression, and no doubt many will discount it because of that. I will say that I think the standard unit works fine, and several arrays side by side works fine also, and takes up considerably less depth than an array spaced like my 8 pipe array so if space front to back is a concern I would definitely stay with a straight line array like the standard room lens.

I think that there are probably any number of ways that larger groupings of pipes could be used to greater effect than simple combinations of the standard units, though finding them is always going to be a problem so feel free to experiment as I did, but I don't know that I would like to try to quantify what frequency range the results will cover just by theory alone. As you start to play with various combinations and spacings, the complexity of what is going on will start to increase dramatically and I'm not certain that equating the width of the total array to an effective low frequency point is particularly valid when there are a lot of gaps between the pipes, though it is for some other diffuser types like QRDs where there are no gaps between cells which are simply areas of staggered depth so the sound waves can never pass completely through the unit.

I am currently contemplating another unit, a 4 pipe unit, in a different corner using an array based on a primitive root sequence. Primitive root diffusors, unlike quadratic residue ones, do not produce a symmetrical diffusion pattern and that could be an advantage in the placement I am contemplating which is why I'm wondering about this as an experiment.

I think that apart from overall width and depth, it is probably important in terms of overall effectiveness that there be some variation in the width of the gaps between pipes, regardless of the placement patterns chosen.

I will also add that the Shakti Holograph is another unit using a vertical array with gaps between them and a variation in depth (ie non straight line placement of the 3 elements) and which ensures that the elements aren't parrallel to each other by incorporating curves in the sides of each element and some angling of them in relation to each other. There are obviously more ways than one to skin this cat :-)

As a result, I suspect we may be seeing the start of another approach to diffusion and that there will be more units coming out which use staggered placement of various numbers of elements separated by gaps, but I wonder if anyone has done a theoretical study of this sort of approach yet. Having such a theoretical study available would certainly make it easier for the DIY enthusiast to tailor arrays to suit specific needs rather than approaching the problem along the lines of "I wonder what will happen if I do ..." which is how I approached my 8 pipe array.

David Aiken

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