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<blockquote data-quote="sundownz" data-source="post: 7273241" data-attributes="member: 549523"><p>Pole vents by themselves provide VERY little voice coil cooling... see this Klippel article on blocking a pole vent vs. leaving it open :</p><p></p><p><a href="http://www.klippel.de/measurements/power-handling-heat-dissipation/thermal-analysis-and-heat-transfer/" target="_blank">Thermal analysis and heat transfer</a></p><p></p><p>"Increase of voice coil temperature The figure above shows the heat transfer of a woofer in a loudspeaker system with and without vent in the pole piece. The air below the dust cap will be ventilated through the open vent, and the convection cooling of the coil is low giving a low bypass factor (pink curve in right diagram). After sealing the vent (shown in the left sectional view), the air is pressed through the air gap, and the high velocity of the air particles increases the bypass factor to 50 %"</p><p></p><p>As far as efficiency... plugging the pole completely with no other means of air release does reduce woofer efficiency a bit. On a Nightshade v.1 (not a super tight gap by any means) this represented a loss of 0.4 dB in my testing -- venting the coil former still maintained most of the benefits of plugging but brought that SPL right back as it released excess pressure but wasn't enough to totally prevent the air bypass over the former. The efficiency loss may be more on something like an MT with half the gap width of a nightshade -- but I didn't go in depth on the MT in testing as it's not my product.</p><p></p><p>There are a few other ways around the efficiency drop such as venting the cone body (which I don't like) or drilling channels in the pole (Fi/AA do this). These will both help reduce the efficiency drop and help keep dust caps glued on.</p><p></p><p>A pole vent can be used effectively when combined with other techniques -- you can see two different techniques between our Z v.2 and SA / NS v.2 lines. A third method was utilized on the E8 v.2 as well... all of which provide substantially more cooling than a simple large, open vent (I have done extensive thermal cycle testing to verify them all). You will note in all three the pole vent is quite small, though.</p><p></p><p>In any event... hope that helps.</p></blockquote><p></p>
[QUOTE="sundownz, post: 7273241, member: 549523"] Pole vents by themselves provide VERY little voice coil cooling... see this Klippel article on blocking a pole vent vs. leaving it open : [URL="http://www.klippel.de/measurements/power-handling-heat-dissipation/thermal-analysis-and-heat-transfer/"]Thermal analysis and heat transfer[/URL] "Increase of voice coil temperature The figure above shows the heat transfer of a woofer in a loudspeaker system with and without vent in the pole piece. The air below the dust cap will be ventilated through the open vent, and the convection cooling of the coil is low giving a low bypass factor (pink curve in right diagram). After sealing the vent (shown in the left sectional view), the air is pressed through the air gap, and the high velocity of the air particles increases the bypass factor to 50 %" As far as efficiency... plugging the pole completely with no other means of air release does reduce woofer efficiency a bit. On a Nightshade v.1 (not a super tight gap by any means) this represented a loss of 0.4 dB in my testing -- venting the coil former still maintained most of the benefits of plugging but brought that SPL right back as it released excess pressure but wasn't enough to totally prevent the air bypass over the former. The efficiency loss may be more on something like an MT with half the gap width of a nightshade -- but I didn't go in depth on the MT in testing as it's not my product. There are a few other ways around the efficiency drop such as venting the cone body (which I don't like) or drilling channels in the pole (Fi/AA do this). These will both help reduce the efficiency drop and help keep dust caps glued on. A pole vent can be used effectively when combined with other techniques -- you can see two different techniques between our Z v.2 and SA / NS v.2 lines. A third method was utilized on the E8 v.2 as well... all of which provide substantially more cooling than a simple large, open vent (I have done extensive thermal cycle testing to verify them all). You will note in all three the pole vent is quite small, though. In any event... hope that helps. [/QUOTE]
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