Speakers: Wide & Flat vs. Skinny & Deep

Why are older speakers (80’s and before) wider than they are deep and new speaker designs are slender and deep?

Somewhere along the line speaker designers realized that cabinet diffraction was a major variable in speaker performance, or lack there of. Realizing that the drivers themselves required specific amounts of cabinet volume to perform optimally the reasonable solution was to turn the cabinet sideways if you will. Cabinet diffraction is simply early reflections generated by the face of the speaker itself. So by reducing the surface area of the speaker face we drastically minimize the early reflections. There are numerous other ways of dealing with this same phenomenon with the use of sound absorptive materials as well as sound diffusion materials. All of which are intended to achieve the same final outcome.