the front speakers is not working
 

Hi everybody!
My car 's model is Honda accord 2002. It has 6 speakers: 2 rear speakers, 2 front speaker in the door and 2 speakers on dashboard. But just 2 rear speakers work. I try to remove the cover and check the front speakers with another soure but it is still fine. Then i check the wire and it 's also ok. Can anyone help me this problem. Thanks a lot.