Help understanding "Suspension Limited"

[peace brainerd]

Elsewhere, in regard to a 9mm xmax "subwoofer" driver I'm considering, I was told that ..

X-max figures can be misleading. This woofer is suspension-limited which means it cannot reach 9mm in a linear fashion.

I tried looking up information on that but it's scant online. I understand that the concept is pretty elementary, the suspension limits the excursion before the coil can actually bottom out, but why the speaker is designed in that way vs allowing the cone to actually reach full stop against the backing plate or, more significantly, how this design actually affects performance, is not explained.

...it cannot reach 9mm in a linear fashion

By "in a linear fashion" does this suggest that a design that was not "suspension limited" would maintain linearity while approaching, and meeting, xmax, a whole lot better than the suspension-limited design? So why make the driver this way apart from providing extra protection to the voice coil? Or maybe the question could also be asked..... why would a subwoofer driver not be designed with suspension limiting unless this trade off were significant?

Basically my question is.. is the curve of power required to move the cone much steeper in a suspension limited design than one that is not? Is the driver much more distortion prone and non linear nearing xmax in such a design? It only stands to reason that in the suspension limited design, as well as the non "SL" design, all other things being equal, including xmax, the first few mm of cone travel in either direction would encounter very close to the same resistance from the suspension in both designs. But the last few mm approaching xmax would encounter considerably more resistance from the suspension in the SL design. The suspension is doing a lot more "reining in" at this point, and the quote above would seem to suggest that it's linearity is correspondingly deteriorating.

[pinkmouse]

Originally Posted by peace brainerd

...and the quote above would seem to suggest that it's linearity is correspondingly deteriorating.

Spot on. Most drivers loose linearity at high excursions, though "suspension limited" may mean different things. As well as your definition above, it may also mean that the driver will travel further than the stated Xmax, but the suspension may then be damaged, so in a way, exactly the opposite. Best just to design a system to give you a good margin of safety either way.

[5th element]

I assume this is in response perhaps to the vifa drive unit. I too had wondered why they'd chosen quite a small half roll surround as it would appear to get in the way at the rated xmax.

One thing that's perhaps worth clarifying here is that Xmax denotes the linear portion of the woofers excursion, where the gap (in an underhung motor) still has coil filling 100% of it's height. Usually the Xmax is exceeded long before you'd whack the coil into the back plate or similar and this is defined as the Xmech.

Either way you would expect a driver to come with suspension elements that would act in a linear way for all of the drivers rated Xmax and then perhaps, to offer a degree of protection, act to put the breaks on before you hit Xmech.

I find it a surprise that vifa would design a seemingly high end driver that would display significantly degraded performance due to the limitations of the suspension. It could very well be that the degradation, (if any actually exists) is only very small. I'd have thought that vifa would have experimented with a larger surround if it seemed at all necessary, but then you don't know. Then again the suspension can do more then simply acting to keep the moving parts in alignment, so perhaps a smaller surround was chosen for other reasons.

Limitations of the suspension will only come into things at high drive levels though and if these exclude 20hz explosions and pipe organs then you're unlikely to encounter them with just music, that is unless you listen at mad SPLs.

[badman]

Originally Posted by 5th element

I assume this is in response perhaps to the vifa drive unit. I too had wondered why they'd chosen quite a small half roll surround as it would appear to get in the way at the rated xmax.

One thing that's perhaps worth clarifying here is that Xmax denotes the linear portion of the woofers excursion, where the gap (in an underhung motor) still has coil filling 100% of it's height. Usually the Xmax is exceeded long before you'd whack the coil into the back plate or similar and this is defined as the Xmech..

Unfortunately, your version of clarity differs from mine

You mean an OVERHUNG motor.

[chris661]

I heard it's simply when BL=70%.

[badman]

Originally Posted by chris661

I heard it's simply when BL=70%.

Several different definitions exist. To me, it's where the motor goes out of normal operation, a more conservative definition than most. IOW if an underhung coil has any portion exit the gap, or an overhung coil motor a portion of the gap with no coil. One of the common Xmax "definitions" is the above plus a 10% fudge factor.

[peace brainerd]

In "layman's" terms, would there be any consensus here on the appropriateness of this driver used as a dedicated sub, in its own cabinet, with a plate amp? Of course that depends on listener's taste, power/spl levels, etc. But obviously there are 12 inch drivers out there that shouldn't be considered for sub duty, regardless of that. This is for 100 percent music use, with eight inch woofers & one inch domes in the mains (2 chan).

More specifically, if the Dayton RSS315HF-4 12" subwoofer, with...

Specifications: • Power handling: 400 watts RMS/700 watts max • VCdia: 2-1/2" • Le: 1.04 mH • Impedance: 4 ohms • Re: 3.3 ohms • Frequency range: 23 - 1,000 Hz • Fs: 25 Hz • Magnet weight: 150 oz. • SPL: 86 dB 1W/1m • Vas: 3.00 cu. ft. • Qms: 3.12 • Qes: 0.58 • Qts: 0.49 • Xmax: 14.3 mm • Dimensions: Overall diameter: 12-3/8", Cutout diameter: 11-1/8", Depth: 5-3/8".

... (and only 35 dollars more) can it be expected to handle even 'moderate' sub duty with much greater aplomb?
/əˈpläm/Noun: Self-confidence or assurance, esp. when in a demanding situation.
Nicely appropriate word in this case.

[badman]

The dayton ref is a very serious 12". Is this in comparison to the Parts Express Vifa blowout?

Vifa NE315W-04 12" Neodymium Woofer

The Vifa is better if you need higher frequencies, otherwise for pure sub duty the dayton is a moderate upgrade.

You should consider the creative sound trio12, for a budget, huge output, subwoofer.

Creative Sound - Product Details

[Arty]

probably a higher xmax would be useless, non-linearity of cone backward-forward movement would be unacceptible. So they used a suspension that limits Xmax before it reaches a certain level.

i em probably wrong, as this would be way too logical.

[peace brainerd]

Is this in comparison to the Parts Express Vifa blowout?

Yes it is. I think I was a little impulsive based on the huge discount, neglecting any better judgement that everything's relative. I've finally come to the conclusion, following careful advice here and elsewhere, that the Dayton would be a wiser choice for my needs.

I"ll follow the general plan for the Dayton 12in HF sealed that is on this page...
Zaph|Audio
...and be less concerned about regrets in the future with it compared to the sealed Vifa sub design. The Vifa would probably be a fantastic choice for a three way full range, where a more dedicated sub like the Dayton might struggle (although it is claimed that this Dayton is no slouch at higher freqs.... anybody considered it in a three way?).

One additional question while I have your attention and I must keep scratching that itch to overthink things? (i know i'm in good company here on that score)

The Dayton 12HF is avail in 8ohm for 20 dollars less than the 4ohm. I have two 100 watt (@4ohms) plate amps from the NHT sale that I can use on this, bridged if necessary. Better in any way to use the 8ohm? Or just stick with the 4 ohm driver with one amp? 4 ohm driver w Both amps? 8ohm driver w both amps? No real difference in performance quality either way?