Dan Brandesky wrote on Wed, 23 December 2009 21:21 |
Thanks for the info, guys! Art, you mentioned the horn should be oriented vertically to get the greatest horizontal dispersion; how exactly does this work?
-Dan
|
The CDP stands for Compound Diffraction Projector, the large and small horn use the diffraction principle fto get wide horizontal dispersion.
From Wikipedia:
“Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Similar effects are observed when light waves travel through a medium with a varying refractive index or a sound wave through one with varying acoustic impedance. Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, x-rays and radio waves. As physical objects have wave-like properties (at the atomic level), diffraction also occurs with matter and can be studied according to the principles of quantum mechanics.”
While diffraction occurs whenever propagating waves encounter such changes, its effects are generally most pronounced for waves where the wavelength is on the order of the size of the diffracting objects.”
In the case of many horns that EV made the vertical dispersion is determined by the horn wall angle, while the narrow dimension makes a wider dispersion due to the small opening relative to the wave length.
The JBL Smith horn ( DSH distributed source horn) uses this effect to get wide vertical dispersion out of a very narrow horn, only 1” or 2” interior vertical height.
Horns with narrow vertical dispersion that are not tall enough exhibit “pattern flip” below the wavelength of the vertical opening. The HF dispersion is determined by the horn wall angle, but at lower frequencies the waves diffract, resulting in a pattern that may go from 30 degrees to 110 degrees over the course of an octave or so.
Art Welter