Kaplan Solutions by D'Addario The Kaplan Solutions Non-Whistling E String is specifically designed to eliminate the whistling sound sometimes heard when the open E string is played after crossing from a lower string. It produces a sweet, warm, rich tone that blends well with the lower strings of the violin. A free ball-end adapter is included with the Kaplan Solutions Non-Whistling E String to allow installation on instruments equipped with a single hook-type (loop-end) E-string fine tuner. This is a steel core string with an aluminum winding.