When a loudspeaker projects sound, the sound waves propagate in all directions rather than just in a straight line due to a phenomenon called diffraction. Diffraction is the bending or spreading out of waves as they encounter an obstacle or aperture that is comparable in size to their wavelength.
In the case of a loudspeaker, the sound is generated by the back-and-forth motion of the speaker diaphragm (cone), which creates compressions and rarefactions in the air. Initially, the sound waves do propagate in a more focused manner in the direction of the cone movement. However, as the waves encounter the surrounding air molecules, they undergo diffraction.
Diffraction causes the sound waves to spread out in all directions because the size of the opening or obstacle (in this case, the loudspeaker) is much larger than the wavelength of the sound waves. The waves encounter the edges of the loudspeaker and diffract around it, leading to the formation of secondary waves that propagate in different directions.
The spreading of sound in all directions is also influenced by the frequency (wavelength) of the sound waves. Higher frequency sounds have shorter wavelengths and are more directional, while lower frequency sounds have longer wavelengths and tend to spread out more.
Therefore, in the absence of boundaries or obstacles that can reflect or absorb sound, the sound waves from a loudspeaker will propagate in all directions due to the phenomenon of diffraction, resulting in a spherical wavefront expanding outward from the source.