Wave equation for traveling waves and their sum
Clear[k1,λ1,ω1, ν,v,L,n]

n=6;
L=1.1;
v= 300;
λ1=2L/n;
T=λ1/v;
k1=2Pi/λ1;
ω1=2 Pi/T;
Animate[Plot[{Sin[k1  x-ω1  t], Sin[k1 x+ω1  t], Sin[k1  x-ω1  t] +Sin[k1  x+ω1  t]}, {x, 0, L}, PlotRange->{{0, L}, {-2, 2}}], {t, 0,T},AnimationRunning->False]

Clear[k,λ,ω, ν,ϕ]

General: phase shift between two waves

Determine : (say for air or N2)

340./(3 10^3)

k=2 π/λ;λ=0.11333;ω=2 π ν;ν=3 10^3;

When running , stop phase at the key values:

ϕ=0
t=1/(3 10^3)
Plot[{Sin[k x+ϕ]Cos[ω t]},{x,0.,0.5}]

Animate[Plot[{Sin[k x+ϕ]Cos[ω t],Sin[k x]Cos[ω t],Sin[k x+ϕ]Cos[ω t]+Sin[k x]Cos[ω t]},{x,0,1.},PlotRange->{{0,1},{-3,3}},PlotLabel->"ϕ  "   ϕ],{t,0,(1/3 10^3)},{ϕ,0,2π}, AnimationRunning->False]