Abstract
Background noise level in buildings is an important issue which can affect task or perception of people. Tangency rating methods like NC, PNC and NR give little indication of the sound quality but criterions such as NCB, RC and RC Mark II are able to assess sound quality. Therefore, the goal of this article was to evaluate background sound quality through determination of NCB in different parts of the Islamic Azad University, Science and Research Campus, Tehran, Iran. Background noise level in 40 spaces was measured through octave band frequency analysis in summer and winter. The results indicated that none of the spaces had balanced noise level. In addition NCB rating in the majority of spaces exceeded ANSI S12.2-1995 standard. Strong correlation between PNC and NCB rating indicated that PNC as a tangency system can represent speech interference level (SIL) acceptably. Previous work by others suggests that NC does not correlate well with NCB. Nevertheless, PNC curves have never become widely used.