Setter's at mike using speech for evil purposes (9)
I believe the answer is:
immorally
'for evil purposes' is the definition.
I can't tell whether this defines the answer.
'setter's at mike using speech' is the wordplay.
'setter' becomes 'I' (the person who set this crossword).
'at' means one lot of letters go next to another.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'using speech' becomes 'morally' (I am not sure about this - if you are sure you should believe this answer much more).
'i'+'m'+'morally'='IMMORALLY'
Can you help me to learn more?
(Another definition for immorally that I've seen is " In a bad way".)