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questions about cone shape and port shape


shadyJ

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A quick couple questions about cones and ports...

 

Does the cone shape actually effect anything, provided that the diameter is the same? There are some nearly flat cones and there are some more heavily concave cones. The concave cones will have more sd, but how much of a difference does that truly make? When I try to visualize it, a cone with more surface area via a more concave shape would require more force and is causing greater pressure but in a more concentrated volumetric area. It seems like simply expanding the diameter would be a lot more efficient than sinking the center of the cone back further for more sd. Anyone have any thought on this?

 

As for ports, turbulence and compression is caused by friction of the air on the interior surface of the port. If that is the case, cylindrical ports would seem to be the ideal shape since they have the least amount of surface area vs volume of air. It would stand to reason, as far as I can see, that any other shaped port would be more susceptible to turbulence and chuffing. So why would anyone use any other shape for a port? Tell me what I am missing here. 

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A quick couple questions about cones and ports...

 

Does the cone shape actually effect anything, provided that the diameter is the same? There are some nearly flat cones and there are some more heavily concave cones. The concave cones will have more sd, but how much of a difference does that truly make? When I try to visualize it, a cone with more surface area via a more concave shape would require more force and is causing greater pressure but in a more concentrated volumetric area. It seems like simply expanding the diameter would be a lot more efficient than sinking the center of the cone back further for more sd. Anyone have any thought on this?

 

As for ports, turbulence and compression is caused by friction of the air on the interior surface of the port. If that is the case, cylindrical ports would seem to be the ideal shape since they have the least amount of surface area vs volume of air. It would stand to reason, as far as I can see, that any other shaped port would be more susceptible to turbulence and chuffing. So why would anyone use any other shape for a port? Tell me what I am missing here. 

 

It may matter for higher freq. drivers -- but less the shape and more the overall size of the cone/diaphragm. As you increase the size of the cone you start to create more beamed / directional sound for the upper freq content. This is why tweeters are small . For low bass the wavelengths are so long that the cone matters not. The shape of the cone should have no reasonable effects on the sound. Kicker uses square cones but its more just a way to differentiate from competitors. With square you can get a little more area in the sub box. (assuming you are using a box)

 

Cones are shaped to be strong which is why they are cones rather than flat discs. That is purely a structural choice. You also see some pro cones with rings or ridges-- those are designed to add rigidity and strength to prevent breakup or flexing. If the cone flexes it can cause distortion and peaks in the response as it resonates.

 

You really can only count the area tangent to the direction of motion, so a convex or concave cone won't have more area than a flat cone. Only the diameter counts for general measurement purposes. -- Good question.

 

You are right about ports, you want laminar flow as much as possible Flaring and less surface area on the sides are important. However, larger port area can trump smaller flared ports which is why you do see slot ports which can maximize the port's surface area in a give box.

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As far as ports go...Technically a round shape has maximal vent area to boundary area, but there are a lot of cases where a round port isn't the best answer. For example fitting an 8" circular port with large flares takes up a lot of space in the middle of the enclosure and a large amount of baffle space. Many times it is easier to fit slot ports with the same area into a more compact shape. They are much easier to bend if needed as well and can be built more easily into the bracing scheme of the enclosure. Things like the Polk power port style of vents perform very well but once you start looking at the total size of the vent and flow-guide plate systems and the greatly increased complexity it often ends up not making sense.  

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As far as ports go...Technically a round shape has maximal vent area to boundary area, but there are a lot of cases where a round port isn't the best answer. For example fitting an 8" circular port with large flares takes up a lot of space in the middle of the enclosure and a large amount of baffle space. Many times it is easier to fit slot ports with the same area into a more compact shape. They are much easier to bend if needed as well and can be built more easily into the bracing scheme of the enclosure. Things like the Polk power port style of vents perform very well but once you start looking at the total size of the vent and flow-guide plate systems and the greatly increased complexity it often ends up not making sense.  

This is one of the reasons cylinder subs are such an economical shape for ported subs. The port can just hang down without getting in the way of anything. You just have to make sure nothing falls in the port. It's a shame that so many people are put off by the cylinder shape, because maybe then other companies other than just SVS would be making them. Hauling a sonotube sub around is so much easier than hauling a big, heavy MDF box around. 

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