I am a latecomer to the party here. After lurking for a while I decided to redirect my budget from of buying a set of HD600 or HD650, or Shure SRH1840's off-the-shelf and instead build a set of Magnum V6's. Based on the research I had time to do, the heritage of the Magnum drivers, and Rhydon's reputation here, my gut told me to commit to the V6 route, even though they had just been introduced and there was little information available on them at the time.
As I have been ordering and accumulating the associated component parts, I have had more time to research my choice and the design of the driver itself. I love good designs. Especially elegantly simple designs, as these are often the hardest to achieve. At first pass the V6 seemed to be just a very straightforward design with no frills. As I have looked further, I have found out just how deceptively simple and sophisticated this design is.
At first glance it appeared that the driver just had a clear plastic grille over the diaphragm to protect it, similar to the stamped metal and fabric protective covers on most designs. I searched "acoustic lens technology" and discovered some of the relative advantages of a round perforated waveguide lens. In actuality, this V6 grille also serves as an acoustic lens, or waveguide. The physical characteristics of the lens are carefully managed to shape the wavefront, and control dispersion which tends to beam on-axis as frequencies climb upward. Further, the cavity between the lens and the diaphragm has a resonance that can be managed to smooth the response curve, and mitigate peaks and nulls. The distance between the diaphragm and the lens, the spacing and size of the holes, their shape, the thickness of the lens are all variable that come into play. So beyond just functioning as a protective grille, I have discovered that the V6 incorporates a carefully engineered acoustic lens.
In my experience with car audio, I observed how some installers would use aperiodic loading where possible. Sealed, ported, and infinite baffle or free-air enclosures are common, but aperiodic loading is less commonly used. Aperiodic loading generally models between ported and sealed enclosures and is thought of to some degree as a frequency-specific leaky sealed enclosure. Aperiodic loading can offer the advantages of smoothing the impedance and response curves of a driver, affects primarily bass frequencies, and the physically resistive aperiodic loading of a driver naturally damps signal overshoot and ringing. The resistive material further tends to damp mid and high frequency reflections within the enclosure. Use of this type of enclosure loading presumes that the front wave and back wave of the diaphragm are isolated from each other (which is somewhat inherent with headphones.) In car audio an enclosure was fashioned just large enough to encompass the driver, then a double grille was attached between which acoustically resistive material (cloth, fiberglass, etc) could be layered. The outermost grille was attached to allow easy removal so that the number of layers could be adjusted for optimum response.
It occurred to me that a similar a loading could be used to tune bass frequencies in an open headphone cup and would be fairly easy to implement utilizing a slight modification of the grille structure commonly used in Grado variant designs. By placing a double grille at the end of the cup, and adjusting the resistive material between the grilles to achieve the desired effect, the bass response could be optimized for a given driver/cup combination, while simultaneously mitigating internal mid and high frequency reflections within the cup
In actuality, correspondence with Rhydon revealed that aperiodic loading is already used in the design of the V6 driver (and Grado drivers as well). It is elegantly incorporated within the driver itself. Essentially the back wave of the driver is controlled by a combination of the fabric membrane and holes spaced around the perimeter of the diaphragm. Careful design in this area can significantly affect bass response, and overall frequency response.
Grado mods that add holes in the fabric ring are altering the aperiodic loading of the driver. Generally, the more resistive the aperiodic membrane and structure is, the higher the bass roll-off point (similar to making a sealed enclosure smaller). Similarly, the less resistive the aperiodic loading, the lower the frequency response can extend, albeit at an increasing loss of damping and control of the cone movement (similar to a ported enclosure where the enclosure or port is too large and the design approaches free-air loading). This is why those who open too many holes in the Grado drivers report loose bass or loss of control. The aperiodic variables can be juggled to tailor the response of a driver while other driver elements remain essentially the same. This accounts for at least some of the variation between Grado models, especially in their bass response.
Symphone's emphasis seems to be on offering an optimized driver that is yet as flexible as possible in its application. Since the primary emphasis is on the driver itself, it is likely that they have not left much on the table in terms of driver design, except the drivers interaction with the cup enclosure itself. In the same way that they have carefully managed the various design elements in the driver, it will interesting to see how they optimize the 3d design (for both the driver and cup assembly combined) which is soon to be released. This approach simultaneously allows the opportunity to design a cup housing that is as inert as possible in its structural design, while at the same time exploring synergies between the driver and enclosure as a total assembly.
Placement of the V6 in a wood (or aluminum) cup enclosure offers opportunity to tune the sonic signature of the total design by bringing to bear the sonic characteristics of the wood itself in combination with those of the driver. The 3D approach offers opportunity to minimize coloration of the enclosure allowing the sonic signature of the driver itself to take precedence and approach the design as a total synergistic assembly.
Exploring the differences between these two approaches is what attracted me to the idea of building two different and polar opposite V6 designs within what I had previously budgeted for one premium headphone. Based on the reviews thus far of the V6 I think it is likely that I may well wind up with two different designs that may equal or exceed what I could have bought off-the-shelf for one headphone.
The learning and interaction with positive and creative culture here at Head-Fi alone has already proven to be worth it, and I haven't even built the V6's yet.
