I have an OS .46 AX with either a 12 x 4, or an 11 x 6, and from my personal experience, I preceive it to be a quiet engine, compared to other .46's I've seen at the field and my .46LA. If I'm the only one flying, its hard to hear it sometimes. If there are other engines running on the ground or in the air, you can pretty much forget about hearing it at all.