From manufacturer: What does the i stand for in the new SR225i from Grado? Improved, that's what! Features are the same as the SR125i, new driver, cable and housing designs, but this headphone has an increased rear air flow, utilizes Grado's larger ear cushion and has closer matched drivers. Air flow is increased by 50% which is achieved through an improved rear metal screen. The use of closer matched drivers and the larger cushions results in an enlarged soundstage, while the improved rear screen frees the headphone from coloration's.