B&W Flared Port

[sianturi]

I recently came across B&W brochure explaining their special flared port which has some kind of small holes (around the flare) similar like the ones in golf ball. They say, the holes will help reducing the turbulence in flared port, and thus enhance the sound quality.

Question:
1. Do these holes have significant impact on the sound quality? And what sound quality does it enhance?
2. Is there any research/experiment measuring the turbulence in loudspeaker flared port in quantitative terms.... say, using fractal/chaos theory?

For question no 2, actually I am curious for the application of fractal/chaos theory in loudspeaker performance measurement. If someone wants to do this experiment, I have some paper regarding chaos/fractal theory & application in the real world system (in this case, the loudspeaker system). Perhaps f4ier or others whose currently studying in college/university, and needs a topic for their final year thesis, this could be a subject....

Regards,

 

[f4ier]

I think the dimples do reduce distortion. I'd imagine the dimples change the aerodynamics of the port so that the wind 'sticks' to the port surface more during high output volumes. Of course, the degree of improvement must be measured.

Thanks for offering the information, but I think I'll pass for now I'm currently working on Crossover Simulator; I find myself lacking the time for anything else since I'm (self-) learning Windows programming and speaker theory at the same time. User-interfaces have always been the source of headaches and delays

Isaac

 

[pinkmouse]

Hi Sianturi

As far as I can remember, from reading pop science books on Chaos and turbulent flow, the dimples cause small localised eddy patterns around their proximity.

Because these are small and attached to the surface of the port, (or golfball), they prevent the main air flow from seeing the sides of the port and therefore causing the main flow to be more linear and efficient.

If the dimples are not present, the resulting turbulent flow in the port is much greater in magnitude and therefore wastes energy and dampens the airflow.

I would imagine this maybe would have an effect similar in magnitude to the difference between an ordinary and flared port, but as I have no dimpled ports around I can't test it.

As I said- this is a simplistic explanation, I have no idea about the math to prove it... (sorry!).

 

[annex666]

Quite simply the dimples are to allow lower port tuning without "chuffing" and work like the dimples on a golf ball (as Pinkmouse quite rightly said).

These dimples create a layer of turbulent air that allows air to flow more quicckly through the port rather than having smooth laminar flow which would have to overcome viscous drag (yes air is a viscous fluid).

On golf balls the dimples break up the air directly in contact with the ball and cut through the air - eliminating viscous drag from laminar flow and making the ball go further.

Simple really - once again A-level physics proves usefull.


Hope this helped?

 

[mefinnis]

Now I need to be really careful here because I'm no engineer, just a soft-brained medico, but ......

If we have laminar flow, then we follow the Hagen-Poiseuille Equation:
Q = Pi.r^4.dP/8.n.l

I agree, n(eta) viscosity comes into play, but flow is directly proportional to driving pressure.

If we create turbulent flow, then the equation goes something like (from a rusty memory):
Q = k.r^2.SQRT(dP)/p.l

Here viscosity vanishes and density (p=rho) comes into play. More importantly flow is now proportional to the square root of the driving pressure, ie. it becomes non-linear.

Now this is where I fail ...... why do we want port flow non-linear with driving pressure, would this not change the frequency behaviour of the port?

Just wondering

cheers, mark

PS: I'm ever the cynic, but it sounds like sales hype to me!

 

[planet10]

I can't tell you how it works -- there have been a couple explanations that on the face of it make sense. Where you could go looking is research done into the surface texture on sharks and how this has been studied to decrease the drag on submarines.

dave

 

[annex666]

Now I need to be really careful here because I'm no engineer, just a soft-brained medico, but ......

If we have laminar flow, then we follow the Hagen-Poiseuille Equation:
Q = Pi.r^4.dP/8.n.l

I agree, n(eta) viscosity comes into play, but flow is directly proportional to driving pressure.

If we create turbulent flow, then the equation goes something like (from a rusty memory):
Q = k.r^2.SQRT(dP)/p.l

Here viscosity vanishes and density (p=rho) comes into play. More importantly flow is now proportional to the square root of the driving pressure, ie. it becomes non-linear.

Now this is where I fail ...... why do we want port flow non-linear with driving pressure, would this not change the frequency behaviour of the port?

Just wondering

cheers, mark

PS: I'm ever the cynic, but it sounds like sales hype to me!

When explaining how this works I didn't imagine getting a quite so intricate responce, but it is much appreciated!

Just to clear things up the dimples create a region over them that is turbulent - there is not a turbulent flow throughout the whole port but merely a thin layer over the dimples.

It is this layer that allows air to pass more easily through the port and does not create non-linearities.

Although if you're worried about non-lineararites what about the simple fact that the port is flared? Did that not strike you as making the flow non-linear?

 

[mefinnis]

Although if you're worried about non-lineararites what about the simple fact that the port is flared? Did that not strike you as making the flow non-linear?

Well, actually, now you mention it ..... I have wondered what the real advantage is in having a flared port

Mind you, graduated increasing diameter doesn't lead to turbulence per se ...... if it did, horns would be a disaster!

I have no problem with dimples reducing surface drag .... hell, the golf-ball manufacturers sure as hell wouldn't do it if it didn't work.

I just have this problem with some of the "science" which creeps into the HiFi world, with very little to really back-it up, just a whole lot of sales-promotion.

This may be real, I have no idea, but I would love it if one of the clever folks out there could give me a clear explanation of how this effect confers a sound advantage.

cheers, mark

PS: please don't give me directional wire, I'm an athiest

 

[planet10]

I have wondered what the real advantage is in having a flared port

A recent article in audioXpress did some imperical research on the flared port and the conclusion was -- if you can use one, why wouldn't you, since it clearly outperformed a the similar non-flared port.

dave

 

[annex666]

Mind you, graduated increasing diameter doesn't lead to turbulence per se ...... if it did, horns would be a disaster!

I think you've misread me - I said that a flared port would lead to non-linearities not turbulence.

Although the air pressure (at any point respectively along the wave) would be non-linear at different points along the flared port this would not lead to a non-linear frequency responce which is the only real matter in question although a flared port may lead to phase differences I'm not sure.

Don't quote me on that!

 

[annex666]

...oh by the way I didn't mention before, but I'm the proud owner of a pair of B&W 603-S3's - these have two of these flared ports one front and one rear. I don't know if they make the sound any better, but they are rather nice speakers - I'm pleased with the sound and they look really sexy too, why not check out the site(I've got the sorento ones).