I used head-phones or ear-phones for preparing IELTS listening. I did exercises form Road to Ielts as well as from Cambridge IELTS books 4-9. After practicing I started scoring 9 in all the tests.
I was sure that examiners would provide us ear-phones or head-phones for the test. When the test started the examiner asked all the candidates to listen the speakers! Yes my dear, it makes a big difference as the general sound could distract our listening concentration.
So, my advice is that for IELTS Listening, do not only use ear-phones or head-phones for your preparation but also familiar yourself with the speakers.