Articulation Class or AC is a means of rating the relative acoustical performance of products, such as ceilings, used in open plan office environments. In the open office, the primary source of distracting noise is human speech and a major concern, therefore, is how to prevent intruding speech from distracting coworkers.
Speech sounds only become intrusive if the words can be understood.
The noise reduction data is then used to calculate the AC value of the product being tested. AC allows us to evaluate how well a product will absorb the noise generated by people talking. Vowel sounds only carry loudness. It is the consonant sounds that are most important in speech comprehension. For example, the consonant sounds are the only difference in the words ball, fall, fawn and malt.