LOOSE STRING FOR DOUBLE BASS Helicore Orquestral '', Mi (E), H6143 / 4 medium tension. Helicore Orchestral Strings for Double Bass are made with a core composed of several braided steel threads, which produces a clear and warm tone. The heart design makes the strings very easy to play under the left hand. These strings are designed for use with the bow, making them ideal for symphonic use. Helicore orchestral strings are also ideal for use on pizzicatos where we offer a very warm sound with less sustain.