their own signal from a separate mix bus on the mixing console; often one of the auxiliary sends ("aux" or "auxes") is used. This configuration is called "aux-fed subwoofers", and has been observed to significantly reduce low-frequency "muddiness" that can build up in a concert sound system which has on stage a number of microphones each picking up low frequencies and each having different phase relationships of those low frequencies. The aux-fed subwoofers method greatly reduces the number of sources feeding the subwoofers to include only those instruments that have desired low-frequency information; sources such as kick drum, bass guitar, samplers and keyboard instruments. This simplifies the signal sent to the subwoofers and makes for greater clarity and low punch. Aux-fed subwoofers can even be stereo, if desired, using two auxiliary mix buses. Directional bass To keep low-frequency sound focused on the audience area and not on the stage, and to keep low frequencies from bothering people outside of the event space, a variety of techniques have been developed in concert sound to turn the naturally omnidirectional radiation of subwoofers into a more directional pattern. Several examples of sound reinforcement system applications where sound engineers seek to provide more directional bass sound are: music festivals, which often have several bands performing at the same time on different stages; large raves or EDM events, where there are multiple DJs performing at the same time in different rooms or stages; and multiplex movie theatres, in which there are many films being shown simultaneously in auditoriums that share common walls. These techniques include: setting up subwoofers in a vertical array; using combinations of delay and polarity inversion; and setting up a delay-shaded system. With a cardioid dispersion pattern, two end-fire subwoofers can be placed one in front of the other. The enclosure nearest the listener is delayed by a few milliseconds. The second subwoofer is delayed a precise amount corresponding to the time it takes sound to traverse the distance between speaker grilles. Vertical array Stacking or rigging the subwoofers in a vertical array focuses the low frequencies forward to a greater or lesser extent depending on the physical length of the array. Longer arrays have a more directional effect at lower frequencies. The directionality is more pronounced in the vertical dimension, yielding a radiation pattern that is wide but not tall. This helps reduce the amount of low-frequency sound bouncing off the