At this level of signal, distortion produced by nonlinear air compression may not be a serious problem, reaching modest (for sound reinforcement equipment) 0.85 % at 1.5 kHz. However, this level of compression distortion is indicative of the high SPL in the chamber that will cause propagation distortion in sound waves traveling through the phasing plug, horn, and further in free air. At higher levels of input signal the air distortion in compression chamber increases further, that presents a problem in its own right even if driver were used without a phasing plug and the horn. But this high level of pressure at the entrance of the phasing plug produces truly devastating effect on sound quality reincarnating in the form of harmful air propagation distortion at the mouth of the horn, and further at the listener's ears.