Exterior noise transmitted to the interior of a structure undergoes absorption due to the existence of materials such as drapes, carpeting, and upholstered furniture. Since internal absorption may significantly affect the actual Noise Reduction of a building, it is necessary to evaluate the absorption adjustment term 10 log S/A, where S is the area of the exterior wall through which noise is transmitted to the room being evaluated, and A is the total absorption in the room. The difficulty arises due to the fact that internal absorption is frequency-dependent - usually increasing with frequency.
In c recent study of the noise attenuation properties of residential buildings, the absorption of typical rooms in 20 separate houses was measured.22 These data it-were used along with dimensions taken from plans for the houses to calculate the term 10 log S/A in each case. The results are given in Figure 26 for Living Rooms, Kitchens, and Bedrooms. As can be seen in this figure, average values for each type of room are reasonably independent of frequency and differ from each other by a small but significant amount.
Additional analysis for typical room dimensions indicated that with two walls exposed (as in the case of a corner room) to the noise source, the 10 log S/A term will increase by 3 dB. The 10 log S/A corrections resulting from this analysis are tabulated in Table 24.
| Interior Space | One Wall Exposed | Two Walls Exposed |
|---|---|---|
| Living Rooms | -4 | -1 |
| Bedrooms | -3 | 0 |
| Kitchens | -2 | +1 |
