I own Howard Low D whistle more than half years, and I realize that the sound isn’t too broad at all, is that cause by the plastic mouthpiece ? or the metal mouth piece will make a broad sound ? Thanks.
Excuse latent stupidity, but what do you mean by “broad”? 
Trisha
Do you latently allude to those which just don’t sing in Tenor? :roll:
If by broad is meant strong or loud tone, I would say that it is characteristic of low whistles to be somewhat soft pitched. This varies. I’ve played Susato low Eb, and it has a nice strong sound, though I doubt even it would hold much ground in an orchestra of fifty instruments.