It really doesn't matter truthfully - BL intermodulation (fluctuating BL levels as the cone moves) is what causes intermodulation distortion.Jonathan wrote:I've never ever seen a dead flat XBL^2 motored anything. ...Depends on your definition of flat, though, whether at the absolute limits or right past center.
And typically, we're talking about some significant fluctuations here... on the order of 10%, maybe more.
The ripples you are looking at there - they are somewhere on the order of a 1% fluctuation.That's not going to be audible.
ALL subs will have some fluctuations like this - with XBL^2 it's predictable, with other subs it's not - take another look at that W7 DUMAX.
If you aren't calling the Brahma flat, you aren't calling the W7 flat. ]Not arguing that, but there are other topologies that give a flat BL to a certain point. Namely underhung.[/quote]
No more so than XBL^2 - in fact less. Just like with overhung, there's an inherent curve to the BL curve.
With underhung, as those short windings move closer to the edges of the top plate, the magnetic flux density is progressively less and less - and as a result, BL drops off.
This is similar to overhung, but the rolloff is slower.
Only dual-gap technologies really directly address this, by setting up a scenario where inherently, as the sub moves, as windings move out of one gap, an equal number are taken up in the other gap - it's not until you start to move out of that gap's field that BL begins to fall - creating a true FLAT BL between those two points.
...and technically, theres' no limitation to two gaps, one coil... Adire had a demo unit at CES two years ago, using three gaps and two coils - and it had something like a 4" one-way throw to it. They had to custom-build an experimental suspension for it.. the Arachnid. It was cool to see in action though.
Show me a picture of a "perfectly flat" underhung... same thing.Show me a perfectly flat XBL^2 or DDD driver and I'll take a picture of myself in a tutu and post it as my avatar. It doesn't exist.
Even if you accept ironing out 1% measurement ripples as nominal, XBL^2 subs will still yield a flatter BL curve, even if you limit the excursion.
It's just like the contour of the earth...
To our perpsective, the ground looks flat, but really it's a progressive curve.
The same is true for an underhung sub... where you might say the overhung is more like the smaller diameter of the moon - a steeper curve.
Yes, underhung has a gentler curve than overhung - but XBL^2 is the concept of the truly "flat earth" that Christopher Columbus was going to sail off the edge of.
(which we didn't think could exist, until a couple years ago... a true "flat" BL curve that is, not a flat earth
)Officially, it's a LGLC sub. Unofficially, you could consider it an LGLC / XBL^2 hybrid, due to that pole-piece cross drilling that they really don't talk much about...W7 is a completely different beast from a typical LGLC design. Can't generalize them, as you can't generalize XBL^2. W7 stays flat to its limits then experiences the dramatic BL rolloff that XBL^2 does past its limits.
[/quote]"The 10W7 isn't flatter - you can even see with the 10W7 that the BL curve has a different shape on the in-stroke, compared to the out-stroke."
As does a Brahma.[/quote]
Well, not really. You can tell by the DUMAX report that the Brahma that was measured had a slight bit of an "off-center" problem... which could have fully been the fault of the DUMAX measurement, since we're manipulating the cone fully by air pressure in the chamber, and the cone position is measured by positioning lasers - the operator tells the machine when the cone is at the "at rest" centered position.
Conversely, the anomolies you see with the W7 aren't issues that could be attributed to a centering issue.
Well, just like damping materials - it's not simply an issue of "intensity" or "frequency" - it's both."A heavier cone would tend to experience resonances later than a lighter competitor, because it will inherently have greater damping properties - pushing those resonances down to a lower frequency, as well."
That's the problem.
So the resonances not only will be a lower frequency, but much less in intensity. The lower frequency also helps them become inaudible - our ears are much less capable of picking up distortions at lower frequencies.
There is no perfect damping solution - but if you compared the sound of a cone with poor damping characteristics to one with good damping characteristics, you'd pick the cone with good damping characteristics every single time, believe me.
It's not so much a problem, as "it's as good as it gets".
The same holds true for any reference product out there - the boundaries can only be pushed so far, at any given point in time - until new innovations are discovered.
What cone material did JL Audio use?
A poly cone.
Now ask yourself "why"? Acoustics?
No - the complicated W-cone they designed mostly required it, due to the complexity and molding required. And even Poly is good enough, when you are talking about subs... even "reference" subs.
What cone material does JBL use on their flagship subs - the GTi's, with the DDD motors?
A VERY coarse, very heavy paper, that makes the Brahma look smooth as a baby's bottom, by comparison. Why? Pure acoustics.
Even look at high-end speakers if you will. Midrange drivers, where cone resonances are a much more serious (much more audible) issue:
DLS is a well known high-end manufacturer.
Look at their "Ultimate" series offerings. In there you'll find poly cones, and even an exotic carbon/kevlar honeycomb structure...
...and what does their Iridium set use? Their "Best of the best" flagship?
A heavy, course, unpressed paper cone.
It may seem intuitively "low tech" - but that doesn't make it sonically inferior.
