Grave and acute
In some schools of phonetics, sounds are distinguished as grave or acute. This is primarily a perceptual classification, based on whether the sounds are perceived as sharp, high intensity, or as dull, low intensity. However, it can also be defined acoustically (acute sounds have a concentration of energy in the higher spectrum, versus grave which has a concentration of energy in the lower spectrum) or in terms of the articulations involved. Acute sounds generally have high perceptual intensity, and in the case of consonants have been defined as those with an active articulation involving the tongue and a passive articulation involving anywhere on the roof of the mouth that a coronal articulation can reach, that is, from the to the region. Grave sounds are all other sounds, that is, those involving the lips as either passive or active articulator, or those involving any articulation in the soft palate or throat. Most acute sounds are , and most coronals are acute. In particular, palatal consonants are acute but not coronal, while linguolabial consonants are coronal but not acute. The distinction can be useful in diachronic linguistics, as conditional sound changes often act differently on acute and grave consonants, consonants are highly