I submitted a PR for configurable volume ~2015 [0]. For as often as I see this complaint in threads about the project, it's a shame that the author isn't interested in implementing it.

[0] https://github.com/tholman/elevator.js/pull/64

[1] https://github.com/tholman/elevator.js/issues/113

[2] https://github.com/tholman/elevator.js/issues/123

[2] https://github.com/tholman/elevator.js/issues/124