Suppose a rectangular enclosure of the same interior dimension $(5$m $4$m $3$m$)$ as in $($a$)$

is simulated numerically by a physical model enclosed by elastic and absorptive partitions

in a x$,$ y$,$ z coordinate system. The thickness of walls, roof and floor is $0\mathrm{.}24$m and the

enclosure is filled with air. Four symmetrical harmonic forces $($F$1,$ F$2,$ F$3$ and F$4)$ of same

magnitude and some phase differences are imposed on the roof of the room enclosure

shown in Figure Q$4\mathrm{.}1.$

The harmonic excitation forces are imposed on the roof of the room enclosure at

frequency of $80$ Hz$,$ the phases of F$1$ and F$2$ are $1$ $,$ and the phases of F$3$ and F$4$ are $2$ $.$

The phase difference between the two pair of forces is $12$ $=.$

Figure Q$4\mathrm{.}2$ shows the computed results of the sound pressure level of the node points at

$($y$=2$m$,$ z$=1\mathrm{.}75$m$)$ where the amplitude of the four applied harmonic forces varies from

$100$N to $800$N at constant phase difference $(12$ $=)$ of $0$

$90.$

Figure Q$4\mathrm{.}3$ shows the computed results of the sound pressure level of the node points at

$($y$=2$m$,$ z$=1\mathrm{.}75$m$)$ where the amplitude of the four applied harmonic forces

$($ NF $500$

$4321=)$ are $500$N at phase difference $$ of $10,30,60$ and $0$

$90.$

Based on the computed results shown in Figures Q$4\mathrm{.}2$ and Q$4\mathrm{.}3,$ can you estimate the

sound pressure level of the same node points at $($y$=2$m$,$ z$=1\mathrm{.}75$m$)$

$($i$)$ where the amplitude of the four applied harmonic forces is $1000$N at constant phase

difference of $60$; and

$($ii$)$ where the amplitude of the four applied harmonic forces is $500$N at constant phase

difference of $45?$

If yes, give your reasons and sketch the predicted figure of the sound pressure level of the

node points at $($y$=2$m$,$ z$=1\mathrm{.}75$m$).$

If no$,$ give your reasons.