A phenomenon of loudspeakers (including horns and tweeters) where the normal dispersion characteristics of the device breakdown and higher frequencies begin to be projected straight out from the device rather than dispersing into the soundfield. To a listener it will sound like the device is only producing high frequencies when standing directly in front of it. Unless specific steps are taken to reduce or prevent beaming it will generally occur when the wavelength of a sound becomes smaller than the diameter of the device (or the throat of a horn). This means that an 18″ speaker begins to get “beamy” at a lower frequency than a 10″ speaker and is one reason why speakers in general aren’t used to try to reproduce high frequency sounds. A horn, to a certain extent, solves this problem, but they still get beamy at very high frequencies. In the 1970’s Constant Directivity horns were developed that vastly improved this performance, though there are some compromises.