Props to fra107 for the idea here: http://www.head-fi.org/t/445027/modify-my-headache-of-grado-325i#post_6505738
I have copied his mod by putting Beyerdynamic DT880 velour pads on my Grado SR80i's. I already modded the Grados by venting 4 holes, felt-dampening the air chamber and driver, replacing the grilles and padding the headband with the foam which the headphones shipped packed inside. I glued a cut-out section of that foam to the headband. It's very comfortable now.
I used Elmer's 3/16" foam board (which is VERY rigid) cut into rings with a circle cutter, quarter-modded (well, slightly bigger than quarter-modded, enough to not cover ANY of the holes leading to the driver) Sennheiser 414 pads and the circular sheets of foam which came with the DT880 pads to construct the adapters to fit the DT880 pads onto the Grados. The 414 pads are glued to the foam board rings. The foam circles are glued to the other side of the foam board rings. You then slip the foam boards into the stretchy inner circle of the DT880s and slip the 414 pads onto the Grados and boom: you have the most comfortable Grados ever.
I had an idea of what to expect from the sound of these before I made them from looking at a graph at Inner Fidelity displaying how all the different Grado pads, including the G-pads, affect the sound signature of SR225is. I figured my mod would affect the sound similarly to the G-pads because they're both circumaural and both add soundstage by distancing the ear from the driver. I confirmed this is exactly what happens by listening to my mod. The mids from around 1,800 Hz to around 3,300 Hz are significantly scooped by about 4 dB, and the treble is quite peaky and sibilant. The good news: 1. This mod makes the super lightweight Grados amazingly comfortable, 2. This mod gives the Grados soundstage, and 3. The scooped mids and sibilant highs can be corrected with EQ.
I loaded up SineGen, a free sine wave generator, and identified three peaks at around 7,500, 9,100, and 12,300 Hz. I then came up with an Electri-Q EQ setting that gives them a nice bass boost (compensating the best I can for the Grados' significant sub-bass rolloff), boosts the mids where the mod scoops them and scoops the treble at the peaks. The result is a warm, fairly flat (aside from the bass boost which is to my personal taste) sound signature which sounds powerful, natural, and speaker-like with its soundstage. I can listen to these for hours and hours now; neither the comfort nor the sound signature are fatiguing.
I believe fra107 has come up with an affordable, viable alternative to the extremely expensive wooden C-pads which have been previously used to mod the DT880 velour pads onto Grados. These Grados are comfortable enough to wear for many hours in a row now. With a little EQ tweaking they sound incredible; they sound far more natural and speaker-like than stock Grados.
Edited by ComfyGrados - 6/7/12 at 12:05am