Most audio engineers will at times monitor using speakers and other times will use headphones. The primary advantage of using headphones is that, if the listener is used to the sound of a particular set of headphones, then when working in different studios or different locations, the listener will have a good reference when using those headphones. Typically the size of the room effects signals below 300 Hz, but this isn’t a factor with advantages are that headphones dynamically compress the sound, so that subtle details can be heard, that might have gone unnoticed on speakers. Also, many listeners use headphones or earbuds on their iPods or other mp3 players, so mixing using phones will better replicate what the sound will be like for disadvantages of headphones include the perception that the stereo field is much wider than it actually is when played on speakers. Also, the subtle details that can be heard on headphones are often lost on speakers. Because of this, some sounds may not be loud enough in the mix. However, the biggest disadvantage is that prolonged use of headphones, especially at high volume can permanently damage hearing.