Can you expand on the benefit of limiting excursion by mechanical means? I understand that it forces the woofer to remain linear, but what is the disadvantage to allowing the motion to exceed linear motion during dynamic passages as opposed to hard limiting mechanically? Does it allow you to run a stiffer suspension providing greater control over the cone motion? I might just be confusing myself at this point. . . Super excited to see the end result of all your work btw!
First consider the application and how much movement is needed.
In this case if the woofer is playing in free air then it might not be required to play down real low anyway. Other woofers will be handling from 150Hz or so and down. So long exertions are not needed.
If it were playing more full range like in a ported box then X-max might be more of a consideration. It all depends on how hard it will be played and to what frequency range.
All woofers have a mechanical limit. Some hit the limit when the voice coil former hits the back plate. In this case these woofers have a bumped back plate to keep that from ever happening. If the voice coil former does not hit the back plate then the woofer will be limited by the surround and spider. This is true for all woofers.
Lets say that a woofer has a 4mm thick top plate and a 10mm voice coil length. That leaves 3mm of voice coil extending above and below the top plate. So for the first 3mm of travel each way the same amount of voice coil is within the gap. However, even as the woofer movement approaches the 3mm range the field strength on the voice coil is already dropping off because the field range extends some beyond the gap. After the first 3mm of movement then the field strength is less as there is less voice coil length within the gap and the control is less. So it is not linear over all of its range if the surround and spider support movements that long.
In this case (with this new woofer) there is a 5mm thick top plate and the voice coil is 19.4mm long. So minus the top plate is 14.4mm or 7.2mm of voice coil each way past the gap. So even as the woofer reaches it's mechanical limit it still has maintained the same field strength over the voice coil.
Here are those same numbers listed on another woofer:
http://www.seas.no/index.php?option=com_content&view=article&id=68&Itemid=9216mm voice coil length, 6mm top plate thickness, linear travel 10mm or 5mm each way... Even though the surround may not allow 5mm each way.
