what's the difference between /ə/ and /ɜ/

AnonymousIs there any difference?!

Yes.

Listen to bed ('bed ) here: http://www.merriam-webster.com/dictionary/bed
Listen to bud ('b?d ) here: http

Hello my friend, I appreciate your answer, it looks it is written /b?d/ in Merriam Webster , but according to Cambridge advanced learners dictionary and longman advanced american dictionary it is this way: /b?d/ , (even if you check the audio of conscious and bud in Merriam you will see their deffent)
Any way I'm just

Anonymous it is written /b?d/ in Merriam Webster , but according to Cambridge advanced learners dictionary and longman advanced american dictionary it is this way: /b?d/

They are the same sound. Some use ? to indicate ? in a stressed position.

Anonymous Hi friendI can't understand the difference between e in conscious (upside down e ) and e in bed Is there any difference?! (Specially in american accent)

The upside down e (?) is the symbol for indistinct, unstressed vowel sounds collectively called the schwa. Here are two links about the schwa in American English that may help.