Golfball ports?

[Zealot125]

I was playing a quick game of golf today, and a friend asked me why

there were dimples in golf balls. So, I thought about it, and

decided that the purpose was to decrease the force of drag on the golf

ball. So, I then went home, and continued to think about my

subwoofer project and porting and stuff, when I thought to myself, hey,

if dimple decrease drag, then what would happen if one used a dimpled

port on a subwoofer. Technically, it should allow air to flow at

a greater rate throught the port, thereby decreasing the required

diameter of the port itself.

Thoughts?

[Zealot125]

Nevermind, forget I said anything. Bowers & Wilkins have

already done it. I guess this is why I should research BEFORE

posting and making myself look like an idiot.

http://www.bwspeakers.com/index.cfm/fuseaction/Op.speaker/file/subwoofers

[sunnysal]

there has been some disagreement expressed by members of this board about this subject. however those "dimples" (various textures are used) are found not only on ports they are now found on aircraft, swimwear, bikewear, helmets, etc. seems that causing some turbulance at the surface of an object allows it to slide more smoothly through the air...tony

[D-MAN]

Do not assume that the same aerodynamic issues that effect the movement of an object through static air to be the same as moving air inside of a static tube.

If what you are inferring is actually valid, then all ducted-fan jet engines would benefit by dimpled interior ducts, and that is simply not the case.

Let alone airplane wing surfaces. Hey, give Boeing a call about this one!

Or patent it quick! Put it on your Cessna and retire.

Dimpled ports are a baseless gimmick intended to sell speakers, kids.

DM

[michael hurd]

No biggie, Polk audio also did this a few years ago.

[sunnysal]

It´s too late to call boeing or cessna, they already use something like this...vortex generators are now commonly seen on the leading edge of wings to creat turbulance in the boundary layer on the upper wing surface...it also has been used in many aerospace applications to reduce heat build up from air friction...

Lexus has dimpled surfaces all over the bottom of thier cars...

my daughter´s racing suit has shark skin surface to do the same thing...

D-man, perhaps you are right that the effect would not be the same or as pronouced in a port but you are way off base poo-pooing dimple´s (or any other surface vortex or turbulance generator) general usage in aero and fluid dynamics...

as I said, lots of disagreement on the board but out in the world it seems dimples rule...tony

[D-MAN]

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

[Zealot125]

Im not sure I agree. If friction increased by dimpling, the golf

ball would not travel as far. An increase in friction should be

directly related to an increase in drag. Therefore, a dimpled

gold bal should have less friction with the air and should travel

further. I could very well be wrong however.

http://en.wikipedia.org/wiki/Golf_ball

Any physics gurus should chime in now, im more of a molecular biology kind of guy.

[michael hurd]

D-man, ever gone curling? If you tried sliding a curling rock on a flat hockey rink, you soon find out that it doesn't go as far, compared to the pebbled suface of a curling rink.

Your comparison to a golf ball is different, however, when a golf ball is struck, how often does the ball spin, and in what directions does it most likely spin? Sounds like something for the Mythbusters to look into, the difference in a smooth golfball and a dimpled ball, and the difference in length.

I still maintain that by dimpling the surface, this reduces the boundary layer friction, therefore, the ball files further, and the curling rock goes farther.

[DrWho]

http://wings.avkids.com/Book/Sports/instructor/golf-01.html

to sum up the website - friction is one of the smaller factors involved

with a golf ball moving through the air. The bigger factor here is the

"hole" in the air that the ball makes as it cuts through. The dimpling

of the ball makes it easier for the air to come in around the ball and

fill up that space (essentially pushing it forward).

In the grand scheme of things, I don't think dimpled ports are going to

make a huge difference on the overall result - heck flared ports don't

even really make a huge difference (and flaring involes a lot more

space). I think I'll just stick to making my port 1/4" bigger in

diamater and 1/2" longer.

[formica]

In the

grand scheme of things, I don't think dimpled ports are going to make a huge

difference on the overall result - heck flared ports don't even really make a

huge difference (and flaring involes a lot more space). I think I'll just stick

to making my port 1/4" bigger in diamater and 1/2" longer.

That's pretty much what it comes down to. If the dimples "actually" reduce

the friction of the air in the port, you should be able to reduce to port length

to achieve the same tuning. Fractions

of an inch seem about right... and not

really worth the effort for the engineering gain. Marketing is a totally different story though...

Rob

[MrMcGoo]

The Klipsch Ultra2 subwoofers are ported. They are about as potent as subs get without spending ridiculous sums. It appears that the slotted ports are not dimpled.

The B&W dimpled port is more likely marketing than physics. A dimpled port would be dead last on the list of things that might improve subwoofer performance.

Amp power, excursion, digital equalization, crossover slope, volume of the box, quality of the motor etc. are several orders of magnitude more important than dimples on the port.

Bill

[colterphoto1]

you guys make my brain hurt. Too early for this.

[Def Leper]

Brain pain indeed.

Some of the stereophile explanations of technical aspects of sound reproduction border on the mystical sometimes, but speculation about golf ball dimples and how that applies to speakers by those with absolutely no clue to the technology involved is a bit painful to read.

Perhaps the confluence of golf and hi-fi is a bad idea. []

[Speedball]

It is my understanding it makes the air flow more freely..........I dunno.

Where is Dragon when you need him? Mmmm....maybe this isn't his specialty.[:^)]

[michael hurd]

Easy way to reduce the air speed and therefore noise, use a bigger port. ( more surface area ) While this sounds all good in theory, you still have to fit the port in the box. ( unless you like the look of a chimney projecting outwards )

You can use elbows on round ports, or "bend" a large long slot port around the box. With some subwoofers, the only option is to use a passive radiator, as you simply cannot get enough port area in the box.

[DrWho]

Easy way to reduce the air speed and therefore noise, use a bigger port. ( more surface area ) While this sounds all good in theory, you still have to fit the port in the box. ( unless you like the look of a chimney projecting outwards )

You can use elbows on round ports, or "bend" a large long slot port around the box. With some subwoofers, the only option is to use a passive radiator, as you simply cannot get enough port area in the box.

I would say a passive radiator is actually a better option (not just the only option - cost considerations aside) because it doesn't take up that precious internal volume (that ports otherwise take up). A great example of this in action would be trying to build an Adire Audio Tumult: the driver allows for a small cabinet that requires a very low tuning point. But to get a low tuning point in such a small cabinet practically requires the cabinet size to double due to the volume taken up by the port! So for the same cabinet size you could run two drivers and twice the passive radiators and have 6dB more output all around and have no chuffing.

Btw, it's easy to make a small port tuned to any frequency, but the trick is to make it large enough so as to minimize the velocity of the air flowing through - the reason air velocity needs to be minimized is due to the turbulence involved as the air transfers from the port to the open air (impedance mismatch if you will). Similar to how hornloading works, flared ports reduce this turbulence by making the transfer a more gradual process (impedance matcher), which in turn reduces the chuffing sound.

The golf-ball dimples actually increase turbulence so it's probably even a dentrimental effect! Nevertheless, the magnitude of the difference would be so small that it's not even worth troubling about...and with a properly sized port it is a mute issue.

[JohnA]

"Or patent it quick! Put it on your Cessna and retire."

I did most of my flight training in a 152 that had hail damage.

We called it "Dimples". It flew 3 to 5 knots faster and stalled

cleaner than any other 152 I ever flew.

[sunnysal]

John,

hail produced vortex/turbulance generators?...ain´t nature a wonderful thing...those dimples allowed the air to better detach from the top wing surface increasing lift...oh yeah!

warm regards,

Tony

[jdm56]

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.