Fala dźwiękowa and other 80,800 icons from Icons8 icon pack follow the visual guidelines of the operating systems: Windows, iOS, Android KitKat, and Material. PNG format is free up to 100x100 px. Icons are availble for download in PNG and vector (SVG, PDF, EPS, and more).
It is a sequence of perfectly vertical lines. The lines are uniform in weight/width, but vary in height. They are all vertically aligned along an invisible horizontal center line. The lines vary from shortest to medium to longest, then back down to shortest. This pattern repeats one more time.