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In Reply to: RE: Nope. posted by hollowboy on June 11, 2008 at 05:03:19
H
With a direct radiator on a flat baffle, the "baffle step" can be calculated as follows:
F=4560/W. This is where W=the baffle width in inches, and F= the requency in Hz where the lower response will be down 3dB. Using a rectangular flat open baffle as an example, the usual justification for mounting the driver asymmetricly in an upper corner is to spread the baffle step effect out to several baffle steps. You have the diagonal dimension from the driver to the furthest corner, the shorter width of the baffle, and the distance of the driver to the nearest edge which will be the smallest baffle step. So theoreticaly instead of having one big baffle step as you would on a flat circular baffle, you have several smaller ones that would hopefully transition more smoothly into each other.
This is not ignored in horn design, though the procedures are a bit different. The illustrations you linked to are from Olson's Acoustical Engineering. On another page Olson investigated the effect of various horn types on the frequency response of a driver. For true horn loading (as opposed to a pipe) the sound waves move from a high pressure area at the throat (near the driver) gradually to a lower pressure area at the mouth. The size of the horn mouth will be the dominant factor in how low the horn can effectively load the driver (asuming the horn length is sufficient), and can be calculated by the size of the sound wave; 13500/F=W, where F= the frequency in Hz of the wave in question, and W=the length of the wave in inches. Using a circular horn mouth as an example, the highest efficiency will be bounded by the circumference equaling 1/2 of a wavelength (in at least 1/2 space), the lowest practical frequency the horn will be able to load the driver to will be 1/4 wavelength (in at least 1/4 space), though a horn with a mouth circumference of 1/8 of a wavelength will work in a corner (at least 1/8 space) but have a steeper bass roll-off. Going back to the horn loading the driver, the horn expansion attempts to couple the driver diaphram to the air in a gradual and controlled manner. So the asymmetry is present in the horn expansion in its axial dimension, and this is analogous somewhat to the asymmetrical baffle in the direct radiator example above. Asymmetrical configurations are seen in bass horns, but their effect on the coverage angle keeps them out of the midrange and treble. I don't know if all this all that simple (and some might find it overly so) but...
...I hope this helps.
Paul
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