\(\def \u#1{\,\mathrm{#1}}\) \(\def \abs#1{\left|#1\right|}\) \(\def \ast{*}\) \(\def \deg{^{\circ}}\) \(\def \redcancel#1{{\color{red}\cancel{#1}}}\) \(\def \BLUE#1{{\color{blue} #1}}\) \(\def \RED#1{{\color{red} #1}}\) \(\def \PURPLE#1{{\color{purple} #1}}\) \(\def \th#1,#2{#1,\!#2}\) \(\def \lshift#1#2{\underset{\Leftarrow\atop{#2}}#1}}\) \(\def \rshift#1#2{\underset{\Rightarrow\atop{#2}}#1}}\) \(\def \dotspot{{\color{lightgray}{\circ}}}\)

Interference

If there are two speakers producing a single wavelength in phase with each other, we can determine whether there is constructive or destructive interference at a certain point in this way:

• Measure the distances from each speaker to the point in question, which are $L_1$ and $L_2$.
• Find the difference between the two, and divide by the wavelength $\lambda$.
• If the decimal part of the result is close to .0, then there will be constructive interference at the spot. (e.g. 3.0, 1.9, 4.1, etc)
• If the decimal part of the result is close to .5, then there will be destructive interference at the spot. (e.g. 3.5, 1.4, 4.6, etc)