Hervejeanne, I have tried a few different Genssler strings. For the sound you describe, Gerolds J-Roque strings could be perfect. Punchy and Thumpy with clarity. They are quite thick and you arco takes a bit of adjustment. Previously I used Oliv DG with various EAs, Pro, Evah, etc. This is my favorite for this Czech bass.
On another bass I have Genssler Rain Worms. Better Arco, more sustain, still an old school and loud Pizz sound. I would start with the JRs.
Hey Decomposer, how would you describe the difference in tone between the rainworm and J-Roque? I've been emailing a bit with Gerold and waiting for him to update with website with audio samples of the rainworm before pulling the trigger on a set. Thanks!
