Helicore Orchestral Series Double Bass String Set 3/4 Size Heavy. D'Addario Helicore Orchestral double bass strings are multi-stranded steel core strings that produce a warm tone quality with excellent bow response. The core design makes for strings that are very easy to play under the left hand. Damping is optimized for arco use, but they also work well for pizzicato applications where a very warm, less-sustaining sound is desired. All D'Addario strings are designed, engineered and manufactured in the USA to the most stringent quality controls in the industry.