Room Mode

Lower frequency below 200 Hz have very long length

wind speed ($v_w$): $343m/s$ Length of 200 Hz $200Hz=\frac{343}{200}=1.715m$

$$\begin{array}{rcl}20Hz& \to & 17.15m\\ 100Hz& \to & 3.43m\\ 200Hz& \to & 1.715m\\ 5000Hz& \to & 6.86cm\\ 20000Hz& \to & 1.715cm\end{array}$$

Another thing about wavelength, a wave will pass through an object smaller than its length without losing power. For example, a sound of 200 Hz can pass through a stone with diameter of 100 cm, or sound of bass can pass through wall.

Fundamental frequency every dimension of the room will have it own fundamental frequency

$F_r=\frac{343}{L}$

mode 1 $=F_r\times 0.5$ mode 2 $=F_r\times 1$ mode 3 $=F_r\times 1.5$ mode 4 $=F_r\times 2$

difference mode will occur in difference positions in along the length of the room

mode 1 will occur in corners of the room. mode 2 will occur in the center

SBIR - Sound Boundary Interference Response

This very close to room mode. The difference is when your room get SBIR and you moving around the room the SPL will stay the same while room mode SPL will change depended on when you are.

So SPL of SBIR will stay the same in every position in the room. It will only change when you move the source of the sound.