Crystal is a little higher pitched and sharper sounding than glass. Harder sound boards give it a louder and higher pitch also. Slate and different wood sound boards mellow the call down some. For instance a glass over aluminum will be higher pitched and more aggressive sounding than a glass over slate. All work great on birds and gives different pitches. All have their subtle differences. This is my experience. I love glass over aluminum and glass over slate. I also love crystal over wooden sound boards. Its all in what sounds good to you. They all kill turkeys but you have to like the sound to gain confidence with the call. If you like the sound , you will use it more and give the call a fair shake.
