Originally Posted by shadyJ
I think that the ULS is using a better driver. Of course, I can't say for sure without knowing the specs of either driver, neither of which are public, but just visually compare at the magnet, spider, and surrounds of each driver:
I'm pretty sure these drivers are not on the same level.
I'm considering purchase of a couple subs and happened on this older thread. One very significant difference between these two drivers is that the HSU unit has shorting rings and the PS unit does not. Shorting rings are copper or aluminum rings inserted around the voice coil or at the ends or both. If you look at the specifications of almost any quality subwoofer you'll notice that the driver has shorting rings as do quality drivers of any size in general. I have no idea why PS didn't include them. It is hard to see why shorting rings would be a major cost driver, but who knows. The lack of shorting rings, especially in a driver in a sealed subwoofer is pretty much a disqualifying factor for me.
Any driver has inductance. If the driver has shorting rings then this inductance doesn't change very much as the voice coil moves in the gap. Without shorting rings the inductance changes a lot which causes distortion. If you look at the distortion measurements for the PS VX15 (a ported design evidently using the same driver as shown above) at Data-Bass, you'll note that the distortion is relatively high and that it goes up with lower and higher frequencies. Rising distortion with higher frequencies is unusual in subwoofers from testing results I've seen online. This rise may be because the inductance seen by the driving signal varies with voice coil position which causes distortion. The distortion level at lower frequencies is likely affected by the same factor although port disturbances and lots of other factors are likely involved, especially as frequency drops and more air has to be moved. .
The "Loudspeaker Design Cookbook," by Vance Dickerson has information on this subject. I believe the author had drivers constructed with and without shorting rings and found much lower distortion with the rings.
Klippel, which makes loudspeaker testing systems that are used in product development and production, has good information on this. For example a poster at http://www.klippel.de/know-how/literature.htm
talks about this, see figure #10 (the label says: "Figure 10: Placing the shorting ring below the gap reduces the voice coil inductance Le(x, i = 0) at negative displacement and gives an almost constant inductance." There are numerous excellent technical papers available on the Klippel site, mostly written at least in part by Wolfgang Klippel, that discuss sources of nonlinearities in loudspeakers. Shorting rings are often mentioned as a key way to fix sources of nonlinearities related to changes in inductance versus displacement. Mr. Klippel also has many published papers available on the AES website
The XBL2 technology that the HSU driver uses is also intended to reduce distortion. A Google search will find information on the technology from the company that owns the patent. It appears to be a very useful technology.
Without a port to minimize voice coil excursions at low frequencies, sealed subwoofers usually have higher distortion from say 15 Hz to 30 Hz than ported designs. HSU's attention to minimizing distortion would appear to be the correct direction for a high performance subwoofer. Distortion performance, already improved at really low frequencies, should be excellent above 30 Hz in the HSU unit. With lower group delay, a slower roll off at really low frequencies, and good performance from small boxes, sealed units have some real advantages.
The ULS is on my short list but I'm not sure what I'll actually get. I do know that for more even response I'll likely get two or four units.Edited by bigguyca - 2/17/14 at 3:02pm