I am looking for some Altec alternative drivers for my 511b horns. I have been trying to find a pair of Emilar drivers but they are almost as expensive as the Altec's. Also diaphragms are expensive. I have been looking at some Renkus Heinz drivers on ebay and there are some SSD-1800-16 drivers and SSD-1801-16 drivers. Looking at the specs it seems the only difference is that the 1800 goes to 17khz and the 1801 goes to 22khz. They both go down to 500hz. Does anyone have experience with either or both driver? I think it would be a no brainer to go for the 1801's but Im not sure what they sacrificed to get the extra 5khz.