I had bought these strings to try on my upright bass and in the first day of trying them I did not like them and whats the biggest bummer is that it turns out I cannot return them. I felt like they do not fit my playing style since they are medium tension and I’m more of a light tension guy when it comes to playing. They sound amazing acoustically especially slapped.
Innovation UB (Ultra-Black) Double Bass Strings are named for their distinctive "Ultra Black" colored outer winding, and work well for a player seeking a fuller, darker-sounding string for traditional jazz and other styles. They are constructed using a flexible braided core with a black tape winding. Unlike most other "black" strings, they can be bowed successfully. UltraBlack strings have a darker tone, like most gut strings, but have the advantage of being a bit more distinct than gut. They offer a less "twangy" alternative to other popular jazz strings. The flexibility of the core (a nylon wound in a "rope" pattern) allows you to really "dig in" without having the string excessively modulate out of tune. Yet the outer wrapping has a hard enough surface to get a nice "growl" or "mwah" from fingerboard interaction. Despite it being marketed as a "Jazz" string for pizz players, the surface of the string reportedly is also equally bow-friendly.