Do speakers have non-radiating nearfield? Antenna nearfield contains energy that is not radiated away,does speaker or any other acoustic device nearfield also have this non-radiating energy element that exist in space and doesnt travel away?
 A: In the electromagnetic case, we say that a component of the field is non-radiating if the field strength of that component decreases with distance faster than $1/r$. Since the intensity of radiation is proportional to the square of the field strength, it follows that the intensity of a non-radiating component decreases faster than $1/r^2$. The total power radiated through a shell of radius $r$ is proportional to the product of intensity and area (which is $4\pi r^2$), so any intensity decreasing faster than $1/r^2$ leads to a decreasing radiated power with distance, limiting to zero power radiated at infinity.
The same argument can be applied to the acoustic case, as long as we make the right identifications between concepts. Sound intensity is analogous to electromagnetic intensity (as they're both power per unit area), and, since acoustic radiated power is proportional to the square of the sound pressure, the pressure plays the role of the electromagnetic field strength. The only thing left to demonstrate is the existence of components of the pressure field that decrease faster than $1/r$.
For an acoustic point monopole source oscillating at frequency $\omega$ with strength $F$, the pressure as a function of distance is
$$p=\frac{F}{4\pi r}e^{i\omega(t-r/c)}$$
which is exclusively proportional to $1/r$. (Just as in electromagnetism, the real part of this complex pressure is the actual sound pressure.) So an acoustic point monopole source has no non-radiating component.
For an acoustic point dipole source of dipole moment $\vec{F}$ and frequency $\omega$, however, the pressure (retaining the same notation) is
$$p=\frac{ik\cos\theta}{4\pi r}\left(1+\frac{1}{ikr}\right)\vec{F}e^{i\omega(t-r/c)}$$
which has a radiating component, proportional to $1/r$, and a non-radiating component, proportional to $1/r^2$. In the near field, the non-radiating component dominates. Similarly, a point acoustic quadrupole source has, in general, a radiative term proportional to $1/r$, and two non-radiative terms, proportional to $1/r^2$ and $1/r^3$, respectively.
As such, acoustic sources with non-radiating components exist, and they're actually quite common. Any acoustic dipole has a non-radiating component.
A: For a distance of order < 1 speaker diameter, the acoustic field strength does not fall off exactly like 1/(distance^2) and it is this zone which is defined as the near field. But as the speaker radiates sound, field energy is continually leaving the speaker, traversing this zone, and then radiating into free space beyond as 1/(distance^2), so it cannot be said that this zone is non-radiative.
