Sound Pressure Comparison of the Plane Wave and Spherical Wave
"Sound pressure by point sources and spherical waves (traditional dynamic cone speakers) are inversely proportional to the square of the distance from the sound source. If the sound pressure is 90 dB for 1m, then for 2m it will be 84 dB, a decrease of 6 dB. On the other hand, the line source (plane wave) is inversely proportional to the distance. If the sound pressure in 1m is 84 dB, in 2m it will be 81 dB decreasing only 3 dB. As seen above, we can say the plane wave is more efficient and does not lose its strength due to distance compared to the spherical wave.
The sound pressure is already reversed at the 4m point which is said to be a relatively short distance in the general practical use.
At a glance catalog specifications of the flat speakers are lower SPL than cone speakers, but at distances more than 5 m, they demonstrate their abilities.
*Note: This graph is not based on an actual survey. It is made from an image comparison that uses the average sound pressure level of the existing product and the theory value about the decrement of a point source and a line source. 1m/1w is the criteria for the comparison of the two speakers (point sources and spherical wave).