Welcome to the Grado Headphone Response Adjustement(s) wiki
As the need for a higher fidelity audio experience continues the headphone truly becomes a compact, somewhat inexpensive, and very portable solution. One such type of headphone is made by Grado Labs http://gradolabs.com/ . Over the years a need was seen for a single source of knowledge for various issues be it positive or negative regarding such headphones. This is where the knowledge can come together with an ebb and flow through your ears to your neighbors. Perhaps creating a synergy of communication between Grado fans as well as other headphone enthusiasts.
The mission of this wiki is to aid in the communication found around Head-Fi regarding Grado headphones and hopefully educate us all on the nuance that is the Grado listening experience. As the author I will keep this wiki up to date as time permits. I will also ensure the upmost professionalism. This said there will be edits, wishfully few, but edits nonetheless. This will keep the wiki fresh and accurate as information streams in.
The first post from Bilavideo sheds light on the brightness of the Grado headphone line. It will give us insite into how to deal with the brightness and why certain headphones such as the SR-80(i) sound much less bright than others.
For a more complete physical look into the Grado mod system see the following link:
The second post is from Maverickmonk.  Provided is another set of modification with a few links to measurements shown for various mods.
Tyll Hertsens provides us with some measurements regarding 3 modified Grado headphones.
Tyll also discusses the mods here:
Solutions to the Grado Brightness
Originally Posted by Bilavideo
Grados sound bright for two reasons. First, they don't filter the driver. Except for the thin grill cloth, which can be treated, what you hear is coming straight off the driver, not what's left after layers of filtration. This makes the Grados more dynamic and unveiled but it also exposes the listener to the dynamics of edgy treble. Sibilance is avoided by the use of pads that limit HF dispersion. The flatter the pad, the more restrained the treble. The larger the pad, the more unrestrained such treble can be.
The second reason for Grado brightness is the open back. Some cans are open to a fault. Some are only semi-open. The more enclosed the can, the easier it is to run an acoustic-suspension system or at least a bass-reflex system, both of which provide a more visceral slam. Grados are not pure open-air cans (If they were, there would be no chamber at all) but the relatively open baffle leaves a low-resonance presentation but one that leaks a lot of bass. Ironically, you can't improve the bass by enclosing the cans because the drivers need volume. Enclosing them actually thins out the sound.
A common mistake is to crank up the volume, in the hope that more volume will equal more bass. But since there's a tonal imbalance, cranking up the volume simply cranks up the imbalance. This leads to the conclusion that Grados are shrill or even grating in their presentation. You need the right amp. Without an amp, a lot of open- and semi-open headphones sound tinny - including the HD800, the T1 and the K701. For those cans, it's de rigeur to match them with the appropriate amp. People overlook this with the Grados because of their low impedence (32 ohms). What those people don't realize is that amping is not just about increasing the volume. I can listen to my HD800 right off my iPod but that doesn't mean I'd want to. The same holds true of the HD650, the T1 and the K701. Just because I can get them to work unamped is no reason I should judge them on how they sound unamped.
I can take any Grado and plug it into a better amp and get a much fuller sound. Right now, I have an M^3 with STEPS and a variable bass boost. With that amp, I can swap out the little pads and pop on the jumbos, which gives me more soundstage, though it thins out the bass. I can then dial up the bass. Once I have the right balance, I get the best of both worlds. With my M^3, you'd think you had purchased a different set of headphones altogether.
Of course, there are some cheap tweaks you can make if you still want to run your Grados unamped:
1. You can switch to smaller pads if you simply want to restrain the HF while bringing up the bass. Flats provide the most radical change. You'll lose soundstage but the bass will be thumping. If it's too muted, a little snip with the scissors will enlarge the center ring, opening up more HF.
2. If you want more bass but without losing soundstage, you can tape the outside of bowls. A little bit of electrical tape around the sides of the bowls will give you more thump. I've tried taping the bowls all around and found it muddied up the presentation, which is another reason I hate leatherette pads, the basshead's friend. A lot of headphones with slamming bass use the leatherette pads, but at a serious cost in clarity.
3. If you want to radically free your Grado's bass, open up the chambers and pop out the holes on the back of the driver. After doing so, you'll have to blow and shake any debris that fell into the driver. This will radically improve the airflow. Afterwards, you may want to damp the insides of the driver with $8 worth of adhesive felt. To do this, you'll need to buy two kinds of felt stoppers sold at Lowe's, Home Depot, Builders Square and True Value. The first kind is the little round stopper (which look like nickel-sized coasters with a rubbery-adhesive back and a felt front). The second is a felt "roll" which can be used to line each chamber. The felt helps indirectly with peakiness. It also cuts some of the mid-bass resonance you get from popping the driver holes. The result of these two tweaks is to kick up the bass while refining the presentation.
4. If you find, after making the above tweaks, that you actually crave MORE HF, you're in luck. You can now switch to jumbos and get all the benefits that come with that. Jumbos provide a larger soundstage, more HF extension and greater comfort. They also temper the midrange, allowing you to kick up the volume and increase the bass (since the holes equalize the tonal balance).