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In Reply to: RE: baffle shape for horns posted by hollowboy on June 11, 2008 at 16:27:18
H
It's difficult to extend these speculations to real world horn applications. If you make Horn A an exponential horn, you probably would have an issue with mouth reflections with this horn used in the mid-range. This type of horn is generally not used nowadays in the midrange for this reason, however many of the classic radial horns used exponential horns in their seperate sections, and they can sound very good. The exponential horn has no trouble going down to its predicted bass cut-off though, as can be seen in Olson's chapter on horns in Ac. Eng.
If you make Horn A a tractrix horn, you could have an issue with the horn not going down its bass target as defined by the mouth size. The reason for this is that you start with the mouth size, and the length of the tractrix horn follows from the tractrix curve. With horns with the same mouth sizes, the exponential horn will wind up being longer than a tractrix horn. If the tractrix horn ends at 90 degrees to its axis, mouth reflections start to become a non-issue. This is the primary advantage of a tractrix horn over an exponential horn, the exponential horn never reaches much more than a certain degree angle with the axis, and the expontial horn therefore can be extended to infinity. The exponential horn (and its relative the hyperbolic horn) are more "pipe like" than a tractrix horn, and are prefered for bass horns, but the tractrix horn is generally prefered for a mid-range horn for the above reasons.
It's dificult to fit Horn B into all this, as just making the mouth rectangular would imply that this horn has a bigger mouth than Horn A. It's difficult to achieve parity in comparing different horns frequently. If you take an exponential horn and put an extension on the mouth that continues to 90 degrees from the axis, you wind up with a horn that starts to look more like a tractrix horn. So does this make it a better horn? Well, it may make it a better midrange horn, but it may not necessarily work better as a bass horn depending on the scale. Just puting a rectangular mouth on a horn will not guarantee a better horn. Symmentical round tractrix horns (and nominally symmetrical square tractrix horns, if you buy Voigt's rationale) are known for having very tight on axis frequency response. The usual motivation for adapting a more rectangular mouth would be for a different coverage pattern, at the expense typicaly of some of that tight on axis response. This is a gross simplification of course, and leaves out what the driver contributes. Terms like tractrix and exponential start to lose their meaning if you are making an arbitrary curve/expansion in 2 of the walls in the horn so as to connect the driver to the a rectangular mouth, in order to make 2 of those walls fit in with the first 2 walls which have been established as a familiar horn curve (tractrix or exponential for example). And what do you call this new horn? If you start with a tractrix curve in the top and bottom, and use a conical expansion in the side walls, is this a tractrix horn? Well, a bit less than half of the horn is conical, and so the horn will have some characteristics of both types. So we've gone from the simple to complex.
Muddy waters ahead!
Paul
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