Speech Transmission Index and Articulation index in the Context of Open Plan Offices
Euronoise 2009 date:26-28 October 2009
The evaluation of the acoustical comfort in an open plan office typically involves a rather complex acoustical analysis. Many parameters, such as the number of square meters per employee, the shape of the room, the absorptive properties of interior surfaces and background noise levels, but also the nature of the activities of the users, are determining factors.
Due to the quite complex character of this kind of multisource environment, the way to assess the acoustical comfort differs from country to country. Often, the reverberation time is taken into consideration. However, since furniture and screens are partitioning open plan offices, the global reverberation time is not an adequate quantity to fully describe their acoustical comfort.
An alternative way to describe the acoustical comfort requirements for an open plan office is by stating the wanted minimal speech privacy together with the desired maximum value of background noise. To define speech privacy (as the opposite of speech intelligibility), two generally accepted approaches are known: the Articulation Index, and the Speech Transmission Index, or similarly the U50 value.
In this article, the feasibility to describe the speech privacy in open plan offices is compared between the Speech Transmission Index and the Articulation Index. The comparison is performed for 16 architectural setups that differ in the value and positioning of acoustically absorbing surfaces, and the placement of furniture elements that act as acoustical screens.