Coincidence

Professional Definition
> Coincidence – resonance when the length of the incident wave trace equals the length of the flexible wave in the plate.

It causes a sharp drop in the insulation of the partition above the cutoff frequency.

## Acoustics in Simple Words
The surfer adjusts the speed to the ocean wave, allowing them to "ride" it effortlessly. The sound "jumps" in rhythm with the wall.

## Summary
The primary reason for the reduction in insulation of homogeneous partitions in the mid-frequency range.