Jonathan wrote:The main things that limit the Brahma/XXX are the soft parts. It isn't the best suspension design or cone assembly. XBL^2 isn't what hinders the high frequency performance of the subwoofer, really I'd say that's the one thing that really makes the sub shine.
I don't see what you are referring to, truthfully.
Take a look at it's DUMAX measurements:
http://www.adireaudio.com/Files/DUMAX/BrahmaDumax.pdf
The nice thing about DUMAX (and Klippel) is that they measure the sub... not so much dynamically (as Klippel can), but across excursion, and in both directions.
If you look at the KMS curve (suspension stiffness), you'll see that the suspension has a very linear suspension, right out virtually as far as the sub's linear excursion capabilities - and very nearly to the sub's mechanical Xmech limits - where it then stiffens dramatically.
And the cone assembly is very rigid paper - which has basically the best stiffness to mass ratios, as well as the greatest self-damping characteristics.
Oddly enough:
Long voice coils produce a really nasty lower midrange spike. This isn't completely taken away even with a 4th order crossover, and even if it were completely cut off, it would still show up with 3rd order distortion. The subs tend to be a bit more localizable due to this. Inductance is higher. Motor topologies can aid this, but take that same motor and cut the excursion and watch inductance benefits follow. But, an inductance measure is different from an Le distortion. High excursion subs suffer from Le distortion (changing inductance with coil motion in relation to the gap) more so than smaller stroke drivers.
...what you are describing are the traditional downsides of a LGLC overhung subwoofer.
And XBL^2 (and DDD as well!) have coil lengths that are smaller - significantly smaller. Granted, not so small that we're in underhung territory, but small enough to be comparable to subs having at least a full order of magnitude lower excursion - and those subs still wouldn't have the distortion reduction of a flat BL curve - those subs would in many ways suffer MORE from intermodulation distortion, because the intermodulation of BL would come on
sooner.
There's a huge difference in listening - and one that many people are a bit hesitant about liking, because it's so different than everything else.
It doesn't sound as violent, it sounds much more effortless, than listening to a comparable sub. It doesn't necessarily sound as "big" at the same dB levels as other subs - because of that reduction in distortion.
Based on what you are describing however, all these things are what should lead you TO a design like the Brahma, and AWAY from an overhung architecture. ]From a mechanical standpoint, high excursion subs have more mechanical noise from surrounds, lead slap, air noise from rear ports, or whatever else applies based on driver design. You also have surrounds that can either dimple at high excursions and cause distortion and noise (ID Max), or you have thick, stiff surrounds to prevent this (pretty much everything else) and consequently drive up Fs in the process and hinder the driver in low frequency extension.[/QUOTE]Fs is always a balancing act.
No one wants a soggy surround... and it helps keep the cone assembly linear in motion as well if it's stiffer, and minimizes those distortions of the surround you mention. All of that is a good thing.
A higher Fs isn't a bad thing either. Everything is good in moderation.
With a design like the Brahma, a few things to note:
Traditional trade-offs with traditional architectures - optimizing a sub for sealed boxes (low Fs, low BL, high Qes, Qts) makes it bad in vented enclosures.
Optimizing a sub for vented enclosures (higher Fs, higher BL, low Qes, Qts) makes the sub a poor performer in sealed enclosures.
Optimizing a sub for neither... I mean "both"
means the sub is a compromised design that works ideally in neither, really... just OK.
Look at what XBL^2 does for that...
Since BL doesn't roll off with excursion (as all traditional design assumptions take into account with traditional subs), the sub behaves better in vented enclosures than it's middle-of-the-road Qts would indicate - it's stronger, if you look at BL in terms of an average across excursion, in operation. Other subs, BL falls off as excursion increases. This has always had to be taken into account.
Not so with XBL^2, so realistically, the motor can control that cone despite the extra pressure forces inside a vented box much better than a traditional sub - even one with a higher BL, and lower Qes and Qts.
And in the same regard, the Fs isn't high either - it's also "middle of the road", so the sub will extend well in sealed boxes - how low do you need it to extend in a sealed box? This sub IS intended for autosound use, right?
When you couple the roll-off of the sub/box with the rising boost you get from cabin gain, having the absolute lowest Fs is really no service to you at all... Lowering Fs typically comes at the expense of efficiency, as well.
In terms of other performance parameters, excursion is superior - so you can brute-force loudness, and can brute-force lowness as well, even in sealed enclosures.
All I'm saying is...
...it's ironic that you are saying you are somehow
opposed to high-excursion subs to me, based on your complaints!
Sounds to me like you just need to take a step back from the IDmax's and W7's on the market.
(you might even note JL's sneaky little trick with the pole vent cross drilling? If you played around with some Finite Element Magnetic Modelling, you'd even see it has a mild effect on the magnetic field forces in it's tall gap - creating almost a watered-down XBL^2 effect Didn't notice that before? 
)
Now that I'm done explaining why I'm confused...
