I need to show an equalizer in my application, but Equalizer need Android 2.3 minimum.
Can I use class Equalizer in Android api <9 with the use of the support library?
No, sorry.
That being said, the source code to it is available, so you could try refactoring it into your own project and using it. However, since the entire AudioEffect framework was not added until API Level 9, I doubt that you will have success.