A term usually applied to vowels. The opposite is lax. The phonetic correlates of tenseness vary somewhat from language to language, or even accent to accent. Generally, tense vowels are closer than the corresponding lax vowels. Acoustically, they have a lower frequency for F1. In some instances, for example General British English, the tense vowels are longer than their lax counterparts: iː > ɪ, uː > ʊ etc., but this is certainly not the case for all accents of English. Many Scottish English accents show no such length differences. The original hypothesis that tense sounds are produced with greater muscular tension has not been confirmed by experimental evidence.