Golfball ports?

[Zealot125]

"Dimples improve the way the air flows over the surface of any object"

I disagree with this statement. It does not necessarily improve the way air flows, it simply changes

the way air flows. Whether this is an improvement or not depends

on the application. In this case, they dont really offer an

explanation why they are an improvement in porting.

[DrWho]

Dimpled ports as marketing ploy? By one of the most respected and, I might add, conservative loudspeaker manufacturers on the planet? Why has no one called their bluff, then?

This from the B&W website:

"If golf balls did not have a dimpled surface, even Tiger Woods would have difficulty reaching 200 metres with his best drive. Dimples improve the way the air flows over the surface of any object. In the case of reflex ports, they offer a significant improvement over simply flaring the port ends in reducing air flow turbulence at each end of the port; so you get less chuffing noise and less compression at high sound levels."

But then on the other hand, they don't make a lot of effort to tell us why this is so. I assume they've done the research. And that is enough for me.

but golf ball dimples INCREASE turbulence.

(Keeping the turbulence behind the ball increases the energy of the air behind the ball, effectively pushing it forward).

[jdm56]

Hey, I don't know! All I know is what I read. B&W is big company, with lots of money to spend on R&D (and on advertising). I've not seen any equally credible entity refute the claim that dimples improve the performance of loudspeaker ports.

My own feeling on the subject is that they probably do help give better measured performance, but that the improvement that the dimples alone give is probably small compared to the contribution of other factors, such as proper port size, placement and flare.

You have to realize that B&W is a company that prides itself on details!

[DrWho]

Hmmm, I don't pay attention to advertising....do they also promote fancy internal wiring? []

[jdm56]

HA -that's a good one! ...No I don't recall any B&W ads that mentioned anything about Monster or any other "audiophool" wire.

They do seem to focus on a pure wave launch, viewing the driver output as something to be purified and gotten out of the way of as much as possible. Putting a horn in front of a driver would probably be "heresy"[] to a B&W engineer!

[dragonfyr]

Refer to the diagrams below:

For laminar (smooth) flow past a sphere, the flow separates very early as shown in the left picture below (again, with a smooth ball). Compare this with a "turbulent flow", caused by a marked or dimpled surface. Flow separation is delayed, as can be seen in the picture on the right. Notice the difference in the size of the separation region behind the spheres. The larger (or early) flow separation causes a larger pressure drag on the sphere (golf ball). The rough or dimpled surface causes "turbulence" which delays or narrows the flow separation. This lowers the pressure drag. On a smooth sphere (golf ball) the faster the ball moves more drag is produced. On a rough sphere speed does not change the drag very much.
http://wings.avkids.com/Book/Sports/advanced/golf-01.html



All the vented-box models feature our unique Flowport system, where a large port flare with sculpted surface terminates each end of the pipe. The flare is precisely dimpled with tiny pits - like the surface of a golf ball - which ensure that the air flows freely down the tube and follows the curvature of the flared ends. Turbulence noise is reduced and far higher sound pressure levels can be attained without compression and loss of dynamics.

For example, the ASW300 are compact active subwoofers designed specifically to complement 300 Series models. The ASW300 subwoofers feature a 200mm (8 in) driver having an extremely rigid cone, to withstand the large forces generated by dynamic bass signals. This subwoofers output is reinforced by a down-firing Flowport, B&W's familiar dimpled port design that reduces turbulence noise to negligible levels.
http://www.bwspeakers.com/index.cfm/fuseaction/Op.speaker/file/subwoofers


The dimpling does not run the length of the port as some seem to imply (or at least as I did as a result of reading the posts and before investigating), but it is limited only to the flare. The effect would be to cause the air flow to delay separation and to follow the curvature of the flare as in a golf ball. Seems very consistent to me!

So it looks as if there is merit to the claim of the air flow delaying separation and following the flare. And this may very well assist in behaving as a smoother acoustic transformer. After all, that is exactly what an electro-mechanical speaker is.

Although I might take issue with the description that "dimpled port design that reduces turbulence noise to negligible levels." and that "far higher sound pressure levels can be attained without compression". Now, does this reduce port noise? Perhaps. At what frequencies, and at what critical points, I can't tell you.

And does it reduce compression? Is the flow at the edge sufficient to offset the total resistance of the total volume of air. I tend to feel that this is a bit over-optimistic.

The claim that air flow follows the contours more effectively appears valid. A very simple and elegant use of the technology. I wonder just how effective it is in practice...

But both claims would be relatively easy to test and validate empirically.

[007]

Not sure if this has been answered or not, but the real reason is counter intuitive Well this is off the top of my head so ill do my best. The dimples are actually designed to increase friction with the air, yes increase! You would think this slows down the flight of the ball and it does, but it also does something else which more than compensates for the air friction. The angle of the club when it strikes the ball causes a torque due to the friction between it and the ball on the ball which sets it spinning backwards very fast. The ball is also elevated and is traveling very fast away and slightly up from the golfer (depending on the club angle). As the ball flys through the air, the air on the top of the ball is moving a lot faster than the air on the bottom of the ball because the dimples are dragging it in the direction as the perceived wind relative to the golf ball or in other words, backwards. The air on the bottom is being pushed into the wind and they both tend to cancel out. So what happens is air on the top is moving faster than air on the bottom and you have Bernoullis principle in effect, or in other words, lift. The higher pressure below the ball is pushing it up and the lower pressure above does not push down as hard so the ball will stay in the air longer. Of course gravity and friction eventually win, but the dimples do account for longer air time and greater distance because flying through the air with a little more air resistance is a hell of a lot less friction than rolling on grass, and belive me, I have hit enough bad shots to know this!

EDIT: Relating to the thread about the increase/decrease of drag, well i know for a fact on golf ball or base balls they are designed to grip the air to manipulate their trajectory. This is done by increasing the air friction. Why its used on ports for speakers, Im not sure at all. But increasing the non-conservative friction force to me seems like it would only decrease the velocity of the air which could possibly lower the amplitude of the noise of the moving air.

thats a wild guess....

[Zealot125]

Some great info in here guys! It is heartening to hope that

someday I might know this much about speakers, golfballs, and laminar

air flow. BUT, in any case, it seems that its about time that I

call up B&W and request MY check (eh Dragonfyr? [])

[Jay481985]

ok guys,

Use an example of a ping pong ball and a golf ball. When you happen to

slam a ping pong ball in the air, what happens? Air actually sticks to

the surface and one side happens to stick more then the other hence the

wicked hooks or drops. Golf balls cause mini turbulances by the dimples

causeing a convection type look. This turbulance happens to have less

friction then the ball not having dimples. Hence no wicked slices or

hooks. Unless you just hit it bad. Air on Air friction is less then air

on solid put it in that way.

[Olorin]

Jay is right on. Dimples on a golf ball decrease friction by

breaking up the airflow over the ball. The ball flies farther and

is less prone to change course (har har) because of spin than if it

were smooth.

[JSharp]

Dimples are used to INCREASE friction, NOT decrease it!

This is used when a control surface NEEDS to "bite" into the air, not slip through it efficiently.

The

golf ball is stabilized by the effect of "biting" into the air,

otherwise the imparted spin forces will cause inadvertant trajectory

changes based on other considerations.

This is EXACTLY the same

as a non-spinning ball fired from a musket barrel as compared to the

same ball fired from a rifled barrel. Hopefully you realize that the

non-stabilized ball is considerably more inacurate, doesn't fly as far

and is not predicable in its path. See the rifled shotgun slug which is

fired from a smoothbore barrel, for instance. EXACTLY the same thing!

DM

Off topic but...

Actually, shotgun slugs are "rifled" to allow them to be fired from

choked barrels without the bore pressures rising above allowable

limits. The "rifling" on the slug does very little, if anything to

impart stability to it. Now a smooth projectle fired from a rifled bore

in a common firearm is another matter altogether since the rotational

speed is typically hundreds of thousands of RPM...

--

Jim

[Jay481985]

remember guys one thing most golfers do not incorporate spin on the

ball unless they put a backspin to stop the ball once it hits the

ground. Most drivers put very little if any spin on the ball. Also

drivers do not have that much of an angle usually less then 10 degrees.

Also 007 I think your refering maybe to those illegal dimpled balls

that you have to hit at a certain direction to get the dimples to work

in your favor