How it works – Multiple speakers are carefully spaced apart and stacked on top of each other and fed the same signal. Since the sound source is increased, an increase in acoustic output is obtained on axis of the array, while at some points off axis of the array it creates a cancellation at varying wavelengths (frequencies) which makes the SPL lower. At some points the cancellation may be nearly complete. This phenomenon is known as combing (see Comb Filter), which leads to another phenomenon of loudspeaker arrays called lobing. Combing is a destructive interference that is usually considered a very bad thing in most traditional sound systems. Line arrays, however, use carefully designed and placed speakers to control the combing and lobing thereby creating a concentrated sound on axis, and moving the combing to the side of the cabinet or speaker array. The result is an ability to control where the sound goes and where it does not, which can be very beneficial in auditoriums and many other applications. For example, a PA can be set up so that sound is focused more on the audience and away from hard surfaces such as concrete walls that will produce excess reverberation. An added benefit is that more acoustic energy gets directed toward the desired spots, which means it takes less overall power to achieve a given SPL. In some of the more advanced systems these directional characteristics can even be controlled by remotely adjusting the relative levels of individual speakers within the array.