# Comfort Distance--A Single-Number Quantity Describing Spatial Attenuation in Open-Plan Offices
## 4 Discussion  
As expected, comfort distance increased strongly when the comfort criterion level \(L_{\rm P,A,C}\) was reduced. Noise annoyance of broadband steady-state noise is usually low when the level is below 35 dB \(L_{\rm Aeq}\)[22]. Using this level as a comfort criterion level is not justified since the comfort distance would exceed 50 m in most offices of our sample. On the other hand, setting the comfort criterion level to 48 dB, as [PERSON] et al. [13] did, is not justified since such a high level is probably no longer perceived as comfortable. For example, [PERSON] et al. [23] and [PERSON] et al. [24,25] suggested that the level of sound masking should not exceed 45 dB \(L_{\rm Aeq}\) to avoid the triggering of noise annoyance due to masking sound itself. It is also notable that [PERSON] et al. [26] showed that people start to raise voice effort due to the Lombard effect when the background noise level exceeds 43.3 dB \(L_{\rm Aeq}\). This supports the use of a comfort criterion level lower than 48 dB. The mean levels during the workday are usually 48-59 dB \(L_{\rm Aeq,8h}\) according to a major survey of offices [27]. This supports also that 48 dB might not be comfortable since it exceeds the average activity noise level. The probability of comfort distance being larger than room length reached zero when the comfort criterion level was 46 dB or larger. Thus, setting the comfort criterion level higher than 45 dB is not supported from this practical viewpoint. In conclusion, it is feasible to set the comfort criterion level at most to \(L_{\rm P,A,C}\) = 45 dB. Among the 26 open-plan offices of Ref. [17], the mean value of \(r_{\rm C}\) was 7.8 m and the values ranged from 3.5 to 30.0 m, when \(L_{\rm P,A,C}\) = 45 dB.  
Figure 6 involves a broad perspective over the eight studies of Table 2. If laboratory study VIII is ignored due to the small room size, the rest of the studies indicate a somewhat similar distribution of comfort distances as Study I [17], where the classification scheme was based upon. All eight studies suffer from selection bias: offices have not been randomly  
Figure 7: Rank ordered comfort distance, \(r_{\rm C}\), as a function of office ID (red triangles) for the 26 offices of Table 1. The proposed limits for classes A–D are indicated by horizontal lines. The figure expects that \(L_{\rm P,A,C}\) = 45 dB.  
selected from the building population. Because of that, none of the studies declare that their data represents the general distribution of acoustic quality in their country. In this light, Figure 6 also suggests that the distribution of room acoustic properties of open-plan offices do not drastically differ from each other in different countries. Figure 6 also represents the best available knowledge on the room acoustics of open-plan offices at the global level. It would be important to systematically analyze the target values and measurement results also from other countries to see the progress in room acoustic design at a global level. This would help in the development of research, business, design guidelines, and target values in the future.  
The classification scheme was created using three criteria explained in Section 3. The scheme may look demanding with respect to the distribution shown in Figure 6 since only a minority of offices can reach class A. For example, an office representing the mean of the 26 offices of Ref. [17], i.e., \(r_{\text{C}}\) = 7.8 m, reaches only class C. Informative (non-mandatory) annex of international standard draft ISO DIS 3382-3 [16] describes that \"Typical values of \(r_{\text{C}}\) with poor and good room acoustic conditions are \(r_{\text{C}}\) > 11 m and \(r_{\text{C}}\) < 5 m, respectively\". This description is supported by our proposal.