There are all kinds of stethoscopes out there now with amplifiers and electronics to make things more clearly audible.
The choice of the “right” stethoscope is VERY personal. I’ve had the same one for 20 years and CRIED, literally cried, when it got lost. Turns out my son had stuffed it into the seat pocket of my car and it was found a couple of weeks later. HE cried when he saw how mad I was! :lol: In the meantime I had “replaced” it with a $350 state-of-the-art one that I barely can stand. There’s nothing like your very favorite stethoscope! 
My advice is to get one that has a variety of earpieces, since that is the MOST important aspect of making sure it works for you, next to quality. A twenty dollar stethoscope is a piece of crap and worth about nineteen dollars too many. But if you’re going to buy an inexpensive one, get one that FITS, and that is all about the ear pieces. The softer, the better.
Generally speaking, shorter tubes give better quality sound, but how close do you really want to be to the horse’s flanks when you’re listening to gut sounds?
I use 14" tubes which are REALLY short, and sometimes I sort of wish they were longer when folks haven’t showered . . . 