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Message: <blockquote data-quote="John_E_Janowitz" data-source="post: 5071167" data-attributes="member: 550657">There are many things to look at within the motor for a woofer that determines its strength.  The type of magnet (ceramic, alnico, neodymium, etc), grade of magnet (ceramic has 3 main grades), size of magnet, the type of steel used and the carbon content, the width of the airgap, type and material of the VC wire, etc etc.  In reality you need to define the goal for your woofer and that will determine all of these aspects.As far as thermal power handling goes, the magnet itself has little to do with this, but the motor strength will.  A more efficient driver will require less power to reach the same output levels.  It is always beneficial to minimize the amount of power needed for a given output.  How tight the gap is also has an affect on power handling. The closer the coil is to the pole, the better it can sink heat to it.  As mentioned, air does not transfer heat very well, so you want the airgap as tight as practical.In the case of our new AV woofers we have tight gaps but also add a highly conductive thick copper shorting ring to the whole pole.  Among other benefits, this greatly increases the ability of the coil to sink heat into the pole.  The steel pole can hold lots of heat but it doesn't absorb it very quickly.  The copper absorbs heat much more quickly where it can then slowly transfer  it via direct contact to the steel pole.  This is the same reason many pots and pans have a copper layer on the bottom, it heats the whole pan quicker.  By doing this, our 2.5" VC drivers will withstand higher continuous power levels than most 3" and 4" VC's.Lower carbon grades of steel have higher magnetic saturation points, meaning they can have more flux going through and into the gap where it is needed.  The more flux that can go through the steel, the less steel you need and the lighter your motor can be for the same motor strength.  The Y35 or Ceramic 5 magnet is about 10% stronger than the Y30 magnet used in most all chinese made drivers.  Many companies simply go bigger on the Y30 magnet vs going with the better grade Y35.  This then adds more weight to the driver and requires larger top and back plates as well.  In the end, the cost comes out about equal but with a lighter driver in the case of the higher grade magnet.  Also as stated above, the biggest issue that affects the strength of a ceramic magnet is it's surface area in contact with the top and back plate.   Going with thicker magnets does not have as much affect as going larger in diameter.  In our TD drivers, the second magnet adds only about 10% BL to the driver, but it is a needed 10% and as stated above gives the physical clearance to not bottom the driver.One of the other big factors in terms of power handling is the VC itself.  Nearly all chinese made VC's have wire that is wound into an adhesive layer that then dries naturally.  These adhesives melt at about 375 degrees F.  A high temperature US made coil like the ones we use are wound, dipped, and baked at 550 degrees F.  When fully cured they will handle temperatures up to 600 degrees F.  In a case like this where you have a high temperature coil and good ability to transfer heat from the coil to the pole, thermal failures are very uncommon.John</blockquote>

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