Yeehaw! Wednesday and I'm bored....
I think Mark's point was that within the bandwidth of a typical subwoofer, inductance is typically a small problem from an audibility standpoint. The roll-off from inductance is theoretically 6dB/octave with a corner frequency that falls well outside of the subwoofer's bandwidth. Of course, the further out of bandwidth the inductive corner is, the less impact things like inductance variation have. From here, we can talk about the limits mass can place on transient response: I know that Dan has said repeatedly that it doesn't but one must wonder aloud how mass can affect frequency response without affecting transient response. Mind you, XBL^2 usually has a leg up in both of these respects due to the small coil. The impacts of inductance and mass on frequency response are readily measurable but, depending on the driver in question, not within concern for many. We also have the related problem of too much bottom end in a vehicle.....
You mentioned above that there is no loss of B as long as the steel that lines the gap isn't saturated as the flux is focused or steered around the rebate. However, the flux density in the gap that is located beside the rebate is less than the theoretical maxiumum: if this were not the case, all XBL^2 drivers would be plain old underhung drivers and the BL curve would not be nearly as flat through it's stroke.
XBL^2 doesn't require a wider gap, either; in fact, the smaller coil usually means less rocking during high excursion (and tighter tolerances become permissible). It does, however, require a taller gap (top plate) which has its own problems.
Still, it is very important that we look at the final result of a product and not the individual pieces! For example, I have said in the past that I think the LMS approach is preferable for subwoofers while XBL^2 is preferable for midrange and fullrange applications; however, suppose a project like Kevin Haskin's Sicko-X: a driver with as much stroke that used an LMS coil rather than an XBL^2 sized coil would have such high inductance and length that its implementation would prove a bit challenging.
All theoretical applications aside, it is the final result only that should be compared.
And this is all an argument about accurate reproduction; as Nick alluded to earlier, most people prefer the exact opposite. Mind you, we're all using stereo recordings, too, so what the hell do we know? //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
I think Mark's point was that within the bandwidth of a typical subwoofer, inductance is typically a small problem from an audibility standpoint. The roll-off from inductance is theoretically 6dB/octave with a corner frequency that falls well outside of the subwoofer's bandwidth. Of course, the further out of bandwidth the inductive corner is, the less impact things like inductance variation have. From here, we can talk about the limits mass can place on transient response: I know that Dan has said repeatedly that it doesn't but one must wonder aloud how mass can affect frequency response without affecting transient response. Mind you, XBL^2 usually has a leg up in both of these respects due to the small coil. The impacts of inductance and mass on frequency response are readily measurable but, depending on the driver in question, not within concern for many. We also have the related problem of too much bottom end in a vehicle.....
You mentioned above that there is no loss of B as long as the steel that lines the gap isn't saturated as the flux is focused or steered around the rebate. However, the flux density in the gap that is located beside the rebate is less than the theoretical maxiumum: if this were not the case, all XBL^2 drivers would be plain old underhung drivers and the BL curve would not be nearly as flat through it's stroke.
XBL^2 doesn't require a wider gap, either; in fact, the smaller coil usually means less rocking during high excursion (and tighter tolerances become permissible). It does, however, require a taller gap (top plate) which has its own problems.
Still, it is very important that we look at the final result of a product and not the individual pieces! For example, I have said in the past that I think the LMS approach is preferable for subwoofers while XBL^2 is preferable for midrange and fullrange applications; however, suppose a project like Kevin Haskin's Sicko-X: a driver with as much stroke that used an LMS coil rather than an XBL^2 sized coil would have such high inductance and length that its implementation would prove a bit challenging.
All theoretical applications aside, it is the final result only that should be compared.
And this is all an argument about accurate reproduction; as Nick alluded to earlier, most people prefer the exact opposite. Mind you, we're all using stereo recordings, too, so what the hell do we know? //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
