I know some of the older members have seen this before but I thought it may be worth quoting this from an old thread for newer members.
So if you find yor speakers are on the bright side after running in intry this. It is much cheper thn changing speakers.
You could use anything that will absorb output from the tweeter handkerchief or some grille cloth.
The guy I have quoted had a Cyrus amp and MA RS8 speakers.