Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Or, for better dynamic range, you could use the Griffin iMic

How can i connect my external mic to my iMac?

The iMic allows you to use any microphone you want, but plugs into the Mac via USB. Therefore you have the benefits of a USB Mic, but with the ability to pair it with a Mic of your choice, from a bargain basement £10 mic to a Shure at £300
 
i try using the audio in socket and didn't work :S is there any setting i should change?

sure you weren't using the headphone input? it's an easy mistake to make
signature_cheekytonguesmile.jpg
, one which i've done several times
 
Please keep in mind that all Macs have a "Line-In" port and NOT a "Mic" port, the two work mechanically different other than having the same socket as a headphone jack. Line-In is not powered, meaning you'll be able to connect an externally powered Mic to that port via a male-male audio jack. Generally, computers that ship with Windows have "Mic" ports, which offer additional power to a mic that does not have it's own power source. Hope this helps!
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.