As you may know. Banshee helmet are named after sound Fx, echo isn't used as term in sound production/engineering e.t.c. The echo effect is actually called delay as it means distinct repetition of same sound with lower amplitude.

But it goes against that banshee bat theme you are trying to achieve, which is actually kinda weird because banshee is entity that "produce" sound and bat echo location is technique which "consume" sound.