We wish to calculate the extent of speech privacy (using Table 2.10) between two offices that share a common partition of area $10 \mathrm{~m}^2$. Each office has a suspended ceiling and the partition separating the offices continues above the suspended ceiling to the floor above. There is an unlined air conditioning duct that extends a distance of $5 \mathrm{~m}$ above each office and penetrates the partition above the suspended ceiling. The penetration may be considered to be well sealed. The duct wall thickness is $0.6 \mathrm{~mm}$ and the cross-sectional dimensions are $2 \mathrm{~m}$ wide $\times 1 \mathrm{~m}$ high. There is one air conditioning outlet of dimensions $0.2 \mathrm{~m} \times 0.2 \mathrm{~m}$ in each office. The configuration is illustrated in Figure 8.53. Partition, ceiling and air conditioning outlet TL data are listed in Table 8.21 . In the table, the TL data for the air conditioning outlets, represent the combined reduction for sound power entering the outlet in the source room to sound power radiated from the outlet in the receiver room. Follow the calculation steps listed below the assumptions to find the speech privacy condition. What would be the best way to improve the speech privacy if it is inadequate?
figure cant copy
TABLE 8.21 TL data for Problem 2
$$
\begin{array}{cccccccc}
\begin{array}{c}
\text { Frequency } \\
(\mathrm{Hz})
\end{array} & \mathrm{TL}_{\text {wall }} & \text { TL }_{\text {ceiling }} & \text { TL }_{\text {outlet }} & \begin{array}{c}
\text { Frequency } \\
(\mathrm{Hz})
\end{array} & \text { TL }_{\text {wall }} & \text { TL }_{\text {ceiling }} & \text { TL }_{\text {outlet }} \\
\hline 100 & 24 & 2 & 15 & 630 & 45 & 3 & 18 \\
125 & 27 & 2 & 15 & 800 & 44 & 3 & 19 \\
160 & 31 & 2 & 15 & 1000 & 43 & 3 & 19 \\
200 & 35 & 2 & 15 & 1250 & 44 & 3 & 20 \\
250 & 39 & 2 & 16 & 1600 & 45 & 3 & 20 \\
315 & 42 & 2 & 16 & 2000 & 47 & 3 & 20 \\
400 & 44 & 2 & 17 & 2500 & 49 & 3 & 20 \\
500 & 46 & 3 & 17 & 3150 & 51 & 3 & 20
\end{array}
$$
You may make the following additional assumptions:
• Sound is incident on and radiates from only the bottom of the duct – not the sides or top.
• There is a substantial partition in the ceiling space to reduce sound transmission
from one office to the next sufficiently so that the sound transmission through
this part of the partition can be ignored.
• Attenuation of the sound propagating in the duct is negligible.
• The ambient noise level in each office due to non-speech noise sources is 35 dBA.
(a) For each 1/3-octave band from 100 Hz to 3150 Hz, calculate the difference in
sound power level incident on the outside of the air conditioning duct in the
source office and the sound power level propagating in one direction inside the
duct.
(b) Calculate the difference in sound power level propagating in one direction inside
the duct and the sound power level radiated into the receiving office.
(c) For each 1/3-octave band from 100 Hz to 3150 Hz, add twice the ceiling TL to
the sum of items 1 and 2 to obtain the TL for air conditioning duct transmission.
(d) Combine the TL for the wall, duct and air conditioning outlets (one in each
room), taking into account the relative areas associated with each, to find the
overall TL in each frequency band.
(e) Find the overall TL averaged over all frequency bands from 100 Hz to 3150 Hz.
Tabulate all results.
(f) Add the average overall TL to the ambient noise level and use this result to enter
Table 2.10 to find the speech privacy condition.
(g) Look at the relative values in the tabulated results to determine what would
increase the speech privacy rating.