Collo,
you wrote:
Quote:
Originally Posted by collo  I don't know that the document you linked to suggested that you could have a 16 inch deepest well AND a 1.1 inch wide well at the same time. They seemed to be independent limits. |
I thought so too. Yet Alton Everest includes a photo of 2x vertical RPG QRD-4311 + horizontal QRD-1911 array in editions (incl. the latest) of his "Master Handbook of Acoustics." See page 266. Here is
the googlebook result. -- he writes "This particular quadratic-residue cluster provides excellent diffusion in the horizontal hemidisc... (p. 265)"
Of course I am struck by the ratio of well width to depth, which is wildly beyond what the calculators recommend. I'm not sure there's more detail to be had for the QRD 4311, but we have the well width and depth and N43 period.
Here is a picture. And
another of it installed. Appears to be made of wood.
Quote:
Originally Posted by collo The only recommendation I've seen for width / depth ratio is the original one proposed by Shroeder, as implemented in the other 2 calculators on the net. With QRDude, this is modified slightly, allowing the width to track the deepest well rather than being based on the design frequency, only when the inverse panel is not going to be used. With the N43, the deepest well is almost the full design depth, so the saving is quite small. |
Yes, and RPG did not follow that. They have extensive measurement facilities.
Quote:
Originally Posted by collo Modelling an N43 to use 1.1 inch wide wells, (fins 1/8 inch), gives a design frequency of 1600hz. This may be what was built. Modelling an N43 to use a 16 inch deepest well gives a recommended well width of 4 3/4 inches. If you built this with 1.1 inch wide wells, you would be a very long way from Shroeder's recommendation. |
Yup. And this strong divergence is what makes the topic intriguing. It's not just any example -- it's considered representative of "best in class" so I hope someone somewhere could shed more light on its theory and function. Or at least, this example may give pause.