GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: Macondo’s Midbass Project – the grown up time.

Post Subject: Resolution of a pixelated flarePosted by jessie.dazzle on: 6/27/2010

Romy wrote:
"...the common rule is to beef up the joints but I propose more elegant approach – to jam the horn by spreading the possible “micro mouths” vibrations. To do is very simple – slice the sections not perpendicular to the horn axis but at angle..."

From this and from the mention of 3/4" plywood, I deduce that the "curved" walls of these horns will likely be described by a series of facets (flat planes). It is said to be okay at these frequencies; this must assume a provision that the "resolution" at which the flare will be "pixelated" is not too coarse. What is too coarse? 1 or 2 planes per meter (ppm)? As the flare is more straight twoards the throat, this figure would logically vary along the flare's length.

It might also be desirable to further randomize the resolution by varying the axial dimension of each plane beyond what is naturally suggested by an economy-based interpretation of the flare.

In some smaller French cities the "autoponts" (overpasses) are made from prefabricated flat planes of equal length; even with a long-wheelbase softly-suspended (i.e. low frequency) luxury car, these equal-length facets initiate an oscilating, bucking motion, transforming even the most luxurious cars into mechanical bulls. This would not be the case if the construction incorporated two different alternating lenghts of prefabbed road. The same logic is applied in the design of tire tread, where the size of the blocks of rubber that contact the road is varied to avoid setting up a harmonic.

Getting back to the horn; staggering the joints relative to (as seen by) the opposing wall would also seem desirable.

To answer Albert's question; how I might make the transition piece:
Assuming a faceted flare, I would make the three walls of this transition piece as a continuation of the horn, from the same 3/4" plywood, so that all sides of the triangle described by throat are tangent to a 7" circle (the triangle would be larger than the circle, tangent to the circle in 3 places); then I would cut a 7" half-circle template and use it to manually "drag in" a radius or fillet made from cheap automotive body filler (polyester resin and solids). I would run this fillet all along the intersecting corner, on out to the mouth.

jd*

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