Xmax and possible cone travel (with likely significant THD increase) are very different things.
Xmax is basically LINEAR cone travel. Non linear cone travel past that point can vary significantly by driver. Some can barely exceed xmax before damage or horrendous sound, others can run a fair way past it(like in this case)
Xmax is basically LINEAR cone travel. Non linear cone travel past that point can vary significantly by driver. Some can barely exceed xmax before damage or horrendous sound, others can run a fair way past it(like in this case)
We don`t really know if the quoted xmax is actually true.
It could be less or more or even a typo.
No absolutely not. Xmax is usually a mathematically derived value calculated from the length of the voice coil and height of the gap. Almost all manufacturers use this convention.
The better way of doing this is to describe at what amount of xmax the driver hits 10% THD at low frequencies. Some drivers reach 10% THD before they reach their actual xmax value because of limitations in their soft parts. Others, like the tymphany sub here, might actually hit 10% THD way beyond their quoted xmax, if the BL curve manages to remain consistent outside of the mechanical xmax.
Agreed.
But if you use real measures you won`t have any "edge" over the competition anymore.
For example...
here is a thread, albeit in german, where someone klippel`d 3 drivers:
IMD, HD, Xmax und Klippel - Vergleich und Bewertung von 3 Chassis - DIY-HIFI-Forum
- Monacor SP-8/150PRO
- Visaton GF 200 (coils in series)
- Faital Pro 8PR200
Calculated xmax:
- Monacor: +-6mm
- Visaton: +-6mm
- Faital: +-5.15mm
(voice coil height/2 – top plate thickness)
(Faital adds another 1/3 top plate thickness)
Measured xmax(10%THD):
Monacor: Xmax10 = 2.1 mm
Visaton: Xmax10 = 3.4 mm
Faital: Xmax10 = 4.5 mm
Yeah it's quite possible. Many SVS drivers are obviously Tymphany, why not the latest one.
It's on the front page of their official website
An externally hosted image should be here but it was not working when we last tested it.
ok, to clear up the confusion,
Xmax, there are many ways that manufacturers use to calculate this,
traditionally it's simply the mathematical calc of the VC winding width minus the top-plate thickness and divided by 2,
that is - voice coil overhang.
this is part of the story on excursion and distortion, but will not tell you much on it's own, as a few people on here have illustrated.
if you look through 'voice coil' magazine you can see drivers with high published Xmax but they have very little if any 'linear' region.
a lot of manufacturers take the Xmax calcs above and add 1/3 or 1/2 the gap height, there isn't really a good reason to do this other than it makes a bigger number,
this seems to be the norm for 'Pro PA' manufacturers,
to take a couple of examples:
STW
gap=36mm VC=57mm Xmax=10.5mm
from (57-36)/2.
driver B. (fictitious but many drivers exist with more-or-less these specs)
gap=5mm, VC=26mm, Xmax=10.5mm
at 11mm excursion both drivers coils are starting to have a percentage of the gap not filled by windings,
at 16mm excursion :
driverB has no windings in the gap meaning there will be next to no force, an zero chance of any more excursion, 100% drop in BL
STW still has 29.5mm of gap with windings present a drop of just 18%
for another example, imagine a 200mm gap height and 200mm coil winding,
the Xmax is zero, but at 25mm excursion the winding in gap only drops 12.5%
92cm vent length!
Also the 6db gain on the sealed graph will quadruple the power needed in the filter range.
the problem with this approach is that it can be system dependent, box tuning etc.. if measured in a system,
if measuring in free air, it won't account for the very small box drivers that may have a compliance non-linearity designed to offset the inherent non-linear behavior of a small box driven by a large Sd.
another thing that puts me off this way of specifying it, is there is no way to prove or disprove the measurement,
geometric methods are at least consistent,
THD from drivers can vary due to pre or post run-in, how much running in exactly, driver to driver variation etc.. i think we'd see a lot of inflation of these figures, as they would be hard to prove.
to me the geometric method is fine, but people need to take into account both the coil overhang and the gap height.
this is like power handling and sensitivity, many people believe more watts equals louder, because they ignore sensitivity!
in reality, you may not need the filter gain, room gain will make up a lot,
I'd really encourage you to try it, the simulations don't show everything,
as for the port length,
if the box is a cube, then it's a vent with 1 bend,
of the box is rectangular, you may or may not need a bend,
you can always reduce the vent by a cm diameter to shorten the port,
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.