Wayne Parham Messages: 18787 Registered: January 2001
Illuminati (33rd Degree)
The four π speaker uses a horn to provide uniform directivity. It is what I call a directivity-matched two-way loudspeaker. Both the three π and four π speakers are this type. What they are designed to do is to crossover from a direct radiating midwoofer to a horn tweeter where directivity matches. This provides better spectral balance off-axis.
I like to use a 90°x40° radial horn with constant directivity in the horizontal plane. This provides good room coverage across a wide horizontal arc. It also limits output at large vertical angles, which do nothing but increase unwanted ceiling slap.
Another type of loudspeaker I make takes this one step further, but requires corner placement: The π cornerhorn. The six π and seven π speakers are cornerhorns. Corner placement limits the pattern to 90° even at low frequencies, where radiation would normally be omnidirectional or at least very wide. This arrangement forces radiation to be limited to 90° all the way down to the Schroeder frequency, making the most constant directivity possible. A midrange horn is also used which has 90°x40° coverage and is implemented with a crossover strategy similar to the DI-matched two-ways, providing uniform 90° horizontal coverage and keeping a pure wide forward lobe of 40° with vertical nulls set outside that.
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