Okay I'm still rather confused. What exactly does the baffle do? And does the material used affect the tone of the 'phones? And what is the velocity of sound? Hahaha.
The baffle is the front wall of a speaker, the part the driver attaches to. Its purpose is to separate the front of the speaker from its back. That's because, on dynamic speakers, the diaphragm and cone push forward and back. Forward motion produces front waves. Backward motion produces back waves. Without a baffle, back waves ricochet off the back wall and end up mixing with front waves. This produces wave cancellations. It's why most speakers don't sound very loud until you place them into a speaker cabinet.
In a
closed system, the back is sealed airtight; the pressure of this back wave is used to reset the cone into its starting position.
In a
bass reflex system, the back waves are vented, either through a passive radiator or a port placed away from the mouth of the speaker. The bass isn't as tight as bass from a sealed "acoustic suspension" system but it's a compromise, especially when the woofer is really just an all-purpose wide-range speaker.
In an
infinite-baffle system, there's no back wall. This is used mostly with subwoofers. Having no back wall means the cone gets no help getting reset. It's less efficient. It takes more energy to produce the same amount of volume. On the other hand, infinite baffles produce less resonance. If you can force enough power through, you can get all the volume you need while the lack of a back wall means you can do it with the least amount of distortion.
There are also
baffle-free systems, where no baffle is required because the sound is not created by compression. This is how dipole systems work, with sound emanating from both sides. Think planars. Magnepan is the Rolls Royce of this setup.
Grados don't have much room for a baffle; they're tubular. There's hardly any room beyond the speaker itself. This adds to a phenomenon known as
the baffle effect. Treble, which is directional, tends to overpower bass, which radiates in all directions. With loudspeakers, baffle compensation involves the use of L-pads (volume controls) to turn down the treble as well as placement of the speaker right up against the wall, so the bass has to reflect off of it.
Different headphones use different strategies for managing the baffle effect. Closed phones seal the driver behind a baffle, which can take up most of the front of the headphone, just like so many loudspeakers. The K1000 got its legendary transparency by utilizing an infinite baffle (there's a plastic separation between front and back but no real back). Not surprisingly, the bass was a bit lacking. The K701 is more constricted. In addition to employing some reflective materials in its rear grill, the K701 also employs a wide disc at its mouth. This allows the use of the wider pads and provides some relief from the baffle effect. It's a strategy that has its fans and critics, since the K701 gets praise for its soundstage but catches grief over its bass (which is more prominent than on the K1000 but still not enough for many) and its clarity when compared to the K1000.
Grado's strategy is obviously to house the driver with an air chamber that surrounds the sides but leaves the rear grill open. This is really a semi-open design. With the back grill open, Grado is hoping to vent as much treble as possible while allowing the bass, which is less directional, to bounce all over the sides of the chamber and get reflected back into the presentation. From a purist's point of view, this provides a less precise waveform. On the other hand, it's the bass that's getting reflected and magnified, which is that part of the spectrum that is left lacking when you play Grados unamped. As bass is slow, to begin with, our perception of bass is poorly directional to begin with, which is why you can put a subwoofer in a corner and never feel as if the bass were coming from "over there."
This is where the material of the air chamber matters. You want something that is going to reflect more bass than anything else. Some materials reflect more midrange and high-bass; others are more effective reproducing bass. I've no doubt that Grado felts the low-end plastics for precisely this reason. There's nothing to the composition of plastic that makes it particularly useful for reflecting lower-frequencies, at least not the plastic used in the Prestige line. Whenever I've vented these plastics, I've found it helpful to either follow-up with damping (to avoid boominess) or to simply remove the back altogether. Using woods like poplar and red oak, I've noticed improvement in the bass, but when switching to mahogany, I've been impressed at how efficiently the mahogany performed in providing so much help to the bass.
Brazilian rosewood has the ultimate reputation in this regard, but since it's illegal to import it into this country, I'm looking forward to hearing what cocobolo will do. After that, I'm going to focus on carbon fiber, which has an amazing velocity of sound, with figures that bury even aluminum.
Velocity of sound refers to the speed with which sound travels through a medium. The composition of the medium either facilitates such transfer or slows it down. Obviously, the faster sound travels through the medium, the more like a driver it behaves, allowing a sharper and clearer amplification of the original signal. According to sources like this one
http://www.engineeringtoolbox.com/sound-speed-solids-d_713.html and this one
http://www.islandone.org/LEOBiblio/SPBI1MA.HTM, sound travels fairly slowly through materials like rubber (40-150 m/s), cork (366-518), water (1433) and lead (1158), but it tends to zip through hardwood and glass (3962), aluminum (4877) and steel (6100). There's more to sound than velocity itself (such as overtones), but carbon fiber's VS (11,000 to 12,000) is appealing. No wonder they make violins, pianos and cellos out of the stuff.
