I had been using a Vandoren B45 as I was under the impression that that was the standard clarinet mouthpiece. I was encountering a lot of resistance and wasn't able to achieve the focused, dark sound that I wanted. I tried several mouthpieces at Sam Ash and the M15 was perfect for me. I was amazed at how effortlessly I could achieve the sound I was looking for. Mouthpieces really do make a huge difference.