Obstruents frequently occur in pairs—one voiced (vocal folds vibrate) and one voiceless (no vibration)—such as /s/ vs. /z/ or /t/ vs. /d/.
They are marked by the presence of noise or silence during the constriction phase. obstruent
An obstruent is a speech sound produced by obstructing airflow in the vocal tract, resulting in a complete or partial blockage that creates noise or friction. Unlike sonorants (such as vowels, nasals, or liquids) which allow air to flow relatively freely, obstruents are defined by their "tight" or "hissy" acoustic properties. Categories of Obstruents obstruent
Obstruent vs. Sonorant Consonants in Phonetics ... - Facebook obstruent
In phonetics, obstruents are divided into three main "flavors" based on how the air is managed: