The subject matter comes up occasionally just like the post by fatswarcat yesterday and that thread covers frequencies when using a non-standard transducer. It would help to be in a sticky topic so those that know about can reference it without doing an extensive topic search if it is not continually being "to the top" (aka ttt) to make it easier to find.
I am used to searching for it with the "something" title by rnvinc, but maybe a post title of Frequency Settings To Match a Transducer.