Spherical Waves

Ideal spherical waves are appealing to the loudspeaker designer since their strength varies only as a function of distance from the source, not with direction. They have ‘constant directivity’ properties and an absence of diffraction.

Spherical waves are easily created when the wavelength is much larger than the source size. A larger source will produce perfect spherical waves only if it moves with the same velocity as a wavefront from a spherical source. Such a sources known as a ‘pulsating sphere’ and may be much larger than a wavelength. Any boundary that is perpendicular to the wavefronts will not cause reflections. This condition is satisfied by conical waveguides with a source centered at the apex. A section of a spherical source at the throat of a conical waveguide will produce perfect spherical waves provided the centers are coincident.

However, pulsating spheres and infinite waveguides are not practical. We will now explore some alternative sources, some of which may be fabricated using known techniques.

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