# An Estimation of Speech Privacy Class Based on ISO Parameter
Standard ASTM E1130-16 [36] introduces another parameter based on the signal-to-noise ratio, describing the state of speech privacy in open-plan offices. This parameter is called the Articulation Index (\(AI\)) [37] and is determined based on measurement results and the introduced form of the speech signal spectrum. The speech intelligibility index (SII) was developed to predict the intelligibility of the speech signal by weighting the importance of different frequency regions of audibility for a given speech test [38; 39]. \(SII\) refers to the calculation of the \(SNR\) at each frequency, with subsequent adjustments for the hearing threshold and masking effects in the frequency domain. SII has a high correlation with speech intelligibility, so it can be considered as a better and more accurate indicator than \(AI\)[40]. A group of researchers led by [PERSON] has extensively addressed the privacy of indoor speech, approaching the problem from diverse angles [25; 27; 41]. Guided primarily by their research, the American standard ASTM E2638 [42] was formulated and adopted. This standard introduces a parameter known as Speech Privacy Class (_SPC_), providing a quantitative measure of speech privacy within a room from the perspective of a potential listener located in an adjacent room. The _SPC_ parameter, as defined in the standard, serves as a measure of speech security and confidentiality, particularly in meeting rooms [43]. Despite its original purpose, it can be applied to various settings, including residential buildings. The _SPC_ value represents the sum of two parameters: non-normalized sound level difference (_D_) between rooms and the ambient noise level (_Lb_) at the potential listener's location. Building upon the North American standard ASTM E2638 [42], this paper introduces a method for evaluating the state of speech privacy in buildings, accounting for parameters commonly used in regions predominantly adhering to ISO standards. Currently, in the part of the world that follows ISO standards, there is no single parameter to quantify the state of speech privacy at the listener's location. This serves as motivation for the research conducted in this paper. The quantification of partition insulation between rooms, following ISO standards, involves utilizing the sound reduction index of the partition. The sound reduction index is determined either in laboratory conditions (_R_) or in situ (_R_) [20]. Typically, the sound reduction index of the partition is expressed as a single-number quantity known as the airborne sound insulation rating _Rw_, or _Rw_ for in situ conditions [44]. This parameter plays a crucial role in various aspects, such as building design criteria, contractor practices, production of building elements, insulation measurements, etc. According to ISO standards, the environmental noise level is quantified through an equivalent level weighted by an \(A\)-filter to consider the influence of the human sense of hearing on sound perception _LAr,eg_[45]. The concept of this paper lies in the utilization of two key parameters--_R'w_ as an indicator of insulation status and _LAr,eg_ as a sound level quantifier--to determine speech privacy levels at the listener's location. In this context, the Speech Privacy Index (_SPI_), expressed in dB, is introduced in this paper as the sum of parameters _R'w_ and _LAr,eg_. The primary focus of this paper is to explore the correlation between the _SPC_ parameter, as defined by the standard, and the proposed _SPI_ parameter through 43 field measurements. The main research objective is to test the hypothesis regarding the mutual correlation of these two parameters, ultimately assessing whether the proposed parameter serves as an effective measure of speech privacy in buildings. Additionally, the correlation between the proposed _SPI_ parameter and the _AI_ parameter used by newer standards in North America will be examined. The paper is organized as follows.