One of the problems in traditional speakers concerns the off axis response of the tweeter. The off axis response of a speaker is determined, essentially, by its diameter and the wavelength of the emitted sound. At some frequency where the driver diameter is comparable to the diameter of the speaker, the sound will begin to beam forward along the speaker’s axis. This effect increases with frequency making a tweeter suffer from forward signal beaming. Yet, tweeters are designed for a flat axial response. Author Macaulay designed a special filter that reduces the forward beaming making the on-axis frequency response flatter.
The Axis Equalizer