Grados have no back. They are open-air cans. They also have no filters between the driver and the ear. What you hear is essentially coming off the driver. Grados don't have much in the way of low bass but by the time you get to 100 Hz, they're all fairly prominent, with a nice, easy glide to the flattest mids you'll find between 500 Hz and 1.5 kHz. Where other headphones roll off early, Grados are prominent through 9 or 10 kHz before rolling off to -7 dB at 15 kHz. All headphone manufacturers say their headphones go from 20-20 kHz but it's all bluster. Most of the sonic range - in most headphones - is between the midbass and high-mids - which is where most of us live.
The open-air design of the Grados help them resolve detail well and manage issues of resonance and distortion. Grados don't have as much bass as a number of closed cans, but they don't sound canny and they certainly don't sound muddy. They sparkle with edge and detail. Having explored other designs, I keep coming back to Grados because they engage the listener very, very well.
On the flip side, because Grados are open, and bass has a tendency to leak out the back, they aren't for everyone. Some find them fatiguing. If you try to crank up the bass by cranking up the volume, you will just succeed in making your ears bleed. There are ways to get more bass out of Grados, but the volume control is not one of them. The cheapest Grados produce more bass by using smaller pads to mute the treble. The SR60s have surprisingly good bass for their place at the bottom of the Grado food chain ($79) but most people go on to other Grados, to get a more open sound. The best all-arounder is the SR225 ($200) which has punchy bass and more sparkle but not so much sparkle that your ears bleed. The SR225 is a fairly mellow Grado, even though it is more open than the SR60.
The top Grados are the RS1, GS1000 and the PS1000, which employ expensive air chambers made of mahogany or mahogany and aluminum. They have the best damping and the best wiring, as well as the cushions/pads that fit well within their emphasis on bringing together the best elements Grado can. Having owned the HD800, the T1 and the PS1000 simultaneously at one point, I can honestly say that the HD800 had the best soundstage, the T1 was the most fun with metal and the PS1000 was the most like being there. When people speak of Grados as having "no soundstage," what they're saying is that the mids are prominent enough that the vocals and instrumentations feel very, very close - as if you were onstage or in the first row. The emphasis is on the mids - not "presence" frequencies high and low. For that reason, most Grados leave you feeling very close to the action. For symphonic music, this can leave some folks feeling claustrophobic; on the other hand, nobody goes to a rock concert to sit in nosebleed. If you want a "polite" distance from the music, check out the Sennheiser HD600/650/800. I loved the HD800's dimensionality (It actually felt 3D). Grado doesn't do space. What you hear will sound like it's coming right off the track, or right off the driver, because it is. On the other hand, I can hear details on my Grado that I don't get with a room full of loudspeakers. Because your ears are superglued to the drivers, and because the emphasis is on the mids, you hear amazing details with the Grados.
You can get amazing details with a lot of headphones, if you spend enough on amps, dacs, interconnects and lossless files, but Grado makes it easy. Grados are also great knock-around headphones - at least in their plastic models. These are headphones you can take anywhere. I wouldn't use them in a noisy environment (where the outside roar invades the mix) or in an ultra-quiet environment (like next to my sleeping wife) but most other environments - including doctors' offices, shopping malls, parks, beaches and even rooms with the TV blaring - have been fine.
