 John Meyer was also involved in the development of the Grateful Dead's Wall of Sound.In 1980, at the behest of Broadway sound designer Abe Jacob, Meyer Sound repackaged the technology of the UltraMonitor into the UPA-1.This loudspeaker had an immediate impact on theatrical sound, but was also notable for its introduction of the trapezoidal cabinet shape, which enabled the construction of curved arrays (flat-front arrays, in common use at the time, result in substantial destructive interference).