Both Etymotic ER2 models, the ER2SE and ER2XR, use the same low-impedance dynamic drivers. That means they are easy to drive, and no amplifier is required. The only difference between the 2 models is the tuning of the lower (bass) frequencies. The “Studio Edition” ER2SE is tuned to have a flat frequency response. The “eXtended Response” ER2XR is tuned to have an emphasised bass, adding 1-2dB to the mid-bass and 3-4dB to the sub-bass. The rest of the frequencies are practically identical to the ER2SE. ER2SE is a great choice for audio creators and musicians on a budget, who require a precise and neutral sound reproduction. ER2SE is also the IEM of choice for consumers who prefer to listen to their music exactly the way it was recorded. ER2XR is favoured by those who enjoy the extra bass presence and body when listening to their music. The extra bass is done tastefully without turning the ER2XR into a bass heavy IEM.