Holy Cr@p is right Cal. Actually, I just realized that I did not compare apples to apples between the driver with enable and the golf ball.
If the Re number for the golf ball is based on ball dia, then the Re number for the driver should be based on driver diameter. Thus the Re number for the driver is 50,000 at 2 kHz for 1 mm stroke. This puts the Re number for the transition between laminar and turbulent flow very close to circa 100,000 value. What this means is that for a 4 inch or 100 mm driver pushing air at 4 kHz and 1 mm stroke, the Re number is 100,000.
However, that 1 mm stroke is quite a lot for some drivers like a Fostex where the EnABLE process is used extensively. Which just means that if stroke is only 0.5 mm then frequency where this is important is 8 kHz or above (the high end only).
OK, so I am now more of a believer that EnABLE may have something to do with tripping the flow of air from laminar to turbulent flow regime. What does it mean for a driver to be pushing air if it switches to the turbulent flow regime? The boundary layer thins out and there is less resistance of the air flow on the cone movement and it will move more freely - almost like the suspension compliance loosens up in a frequency dependent way.
Well this is about as much and as far as I can go with simple scaling arguments. The micro flows around EnABLE dots can be modeled and simulated using computer fluid dynamics (CFD) and some CPU hours on a parallel computer cluster. A grad student should do this for a master's thesis... if it hasn't already been done.
Flow? Sound waves do not flow through a medium, they propagate. Air does not flow to transmit sound, as a body it stays where it is, the air molecules transmit sound by vibrating against each other. Think of an aeroplane wing, it will not generate lift no matter how much sound you bombard it with. You don't get laminar or turbulent flows with propagating sound waves, you get constructive and destructive interference.
Sound does induce fluid or gas flow. Oscillatory flows are well known - check it out. On a timescale of one cycle the air does indeed flow over a distance. Pressure induces flow, Bernoulli equation for example. Sound waves propagate but there is flow associated with them. Look at the simulations on MJK worksheets, an important thing to check in any design is to make sure the Mach number in the port or terminus is sufficiently low, otherwise assumptions of incompressible flow for governing equations (Navier-Stokes) are no longer valid.
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Thanks xrk971, (may I call you x?)
The indisputable fact is that air flow does occur in ports.
Therefore, if we add a raised EnABL pattern inside the port, logically it follows that there must be some impact on that air flow as it hits and flows over the raised pattern. The question that follows is whether the impact on the airflow brings about changes that are audible.
My experience along with others tells me that the changes are audible.
Cheers,
Alex
The indisputable fact is that air flow does occur in ports.
Therefore, if we add a raised EnABL pattern inside the port, logically it follows that there must be some impact on that air flow as it hits and flows over the raised pattern. The question that follows is whether the impact on the airflow brings about changes that are audible.
My experience along with others tells me that the changes are audible.
Cheers,
Alex
Alex,
If the surface treatment changes the flow, which changes how pressure waves develop and propagate, there should be a change in sound. Whether or not one hears them is as you say, the main question. I am just saying that based on scaling arguments and analogy with golf ball dimples, there should be a hydrodynamic effect. I think that the exact shape of the surface treatment may not be so critical as the average interaction or characteristic length. EnABLE patterns look neat and cool and to a certain extent, their exact shape and repeating patterns and cycles add to the mystery. But my guess is that any shape, randomly distributed as long as it has the correct characteristic length will work. Perhaps a distribution of characteristic lengths will let it work over a broader range of flow velocities? In that case, a spackling roller brush and ceiling plaster may be the way to go for a large surface like interior of enclosure and baffle. The effect falls off rapidly with distance from driver so beyond baffle on exterior is not going to be a noticeable impact.
Regards,
X
Btw, if one had a driver the size of the span of an airplane wing, and put that in a giant wind tunnel, and drove it with enough power to induce peak velocities of order 30 m/s, the plane would indeed lift off. The wing needs to have an airfoil profile that is curved on top and flat on the bottom, not plane flat wing using angle of attack.
If the surface treatment changes the flow, which changes how pressure waves develop and propagate, there should be a change in sound. Whether or not one hears them is as you say, the main question. I am just saying that based on scaling arguments and analogy with golf ball dimples, there should be a hydrodynamic effect. I think that the exact shape of the surface treatment may not be so critical as the average interaction or characteristic length. EnABLE patterns look neat and cool and to a certain extent, their exact shape and repeating patterns and cycles add to the mystery. But my guess is that any shape, randomly distributed as long as it has the correct characteristic length will work. Perhaps a distribution of characteristic lengths will let it work over a broader range of flow velocities? In that case, a spackling roller brush and ceiling plaster may be the way to go for a large surface like interior of enclosure and baffle. The effect falls off rapidly with distance from driver so beyond baffle on exterior is not going to be a noticeable impact.
Regards,
X
Btw, if one had a driver the size of the span of an airplane wing, and put that in a giant wind tunnel, and drove it with enough power to induce peak velocities of order 30 m/s, the plane would indeed lift off. The wing needs to have an airfoil profile that is curved on top and flat on the bottom, not plane flat wing using angle of attack.
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G'day x,
I agree with you that almost any raised pattern would impact air flow, yet in practice there is something special about the dimensions of the blocks in the EnABL pattern.
Some years ago I input the EnABL pattern into a ripple tank applet to try and see what might be happening when a wave hits the pattern.
Here is the post - http://www.diyaudio.com/forums/multi-way/119677-enabl-technical-discussion-15.html#post1842872
In relation to treating cabinet edges other than the baffle, I found that in a normal room, the changes are also audible. EnABL seems to mask the audibility of the diffraction of the cabinet enough that the ears struggle to perceive the cabinets as a localised sound source. A ridiculous claim to maken for sure, and yet I stand by it completely. I wouldn't have believed it was possible, until I tested it for myself.
Cheers,
Alex
I agree with you that almost any raised pattern would impact air flow, yet in practice there is something special about the dimensions of the blocks in the EnABL pattern.
Some years ago I input the EnABL pattern into a ripple tank applet to try and see what might be happening when a wave hits the pattern.
Here is the post - http://www.diyaudio.com/forums/multi-way/119677-enabl-technical-discussion-15.html#post1842872
In relation to treating cabinet edges other than the baffle, I found that in a normal room, the changes are also audible. EnABL seems to mask the audibility of the diffraction of the cabinet enough that the ears struggle to perceive the cabinets as a localised sound source. A ridiculous claim to maken for sure, and yet I stand by it completely. I wouldn't have believed it was possible, until I tested it for myself.
Cheers,
Alex
I know your name is Doubtingthomas,
but before you call the Navier-Stokes equations, which describe all liquid and gas flows, and even the propagation of pressure waves (or sound), pseudo science, do your research. If you disagree with something I have laid out, point it out and we can discuss, but you are incorrect to call the Navier-Stokes equations or the Reynolds number (a ratio of momentum forces to viscous forces) pseudo science.
Navier?Stokes equations - Wikipedia, the free encyclopedia
Navier-Stokes equations and sound:
http://www3.kis.uni-freiburg.de/~peter/teach/hydro/hydro06.pdf
Golf ball fluids:
http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml
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Yes, but have you tried a random pattern of similar length scales to see if it also makes a difference? Otherwise, how can you say that the EnABLE patterns are special?
G'day x,
I did try changing the spacing of the blocks, which resulted in a more condensed pattern.
The pattern was different to the prescribed one for EnABL, but was a repeating pattern nonetheless and by no means randomised. I then applied it to the ports of the Voigt pipes I had. The result I could hear was a peak somewhere in the bass frequencies. The prescribed EnABL pattern just sounded more open and natural by contrast.
I realised that developing alternative patterns would likely need more than just ears. In the end I decided to focus on exploring effective placement of the pattern - something which I could do by ear. Which took me from baffles to ports, to external edges, internal panels and even room corners.
Cheers,
Alex
I did try changing the spacing of the blocks, which resulted in a more condensed pattern.
The pattern was different to the prescribed one for EnABL, but was a repeating pattern nonetheless and by no means randomised. I then applied it to the ports of the Voigt pipes I had. The result I could hear was a peak somewhere in the bass frequencies. The prescribed EnABL pattern just sounded more open and natural by contrast.
I realised that developing alternative patterns would likely need more than just ears. In the end I decided to focus on exploring effective placement of the pattern - something which I could do by ear. Which took me from baffles to ports, to external edges, internal panels and even room corners.
Cheers,
Alex
G'day Alex (or should I say G'night because it is like 11 pm where you are),
That is interesting that condensing the spacing shifted the effect to lower frequencies. It may be that you had a reduction of the effect in the HF which let you notice the low frequencies more. Or did you actually measure a peak with a mic and freq response software? Applying it to the listening room! Why not?
Regards,
X
That is interesting that condensing the spacing shifted the effect to lower frequencies. It may be that you had a reduction of the effect in the HF which let you notice the low frequencies more. Or did you actually measure a peak with a mic and freq response software? Applying it to the listening room! Why not?
Regards,
X
I'm thinking out loud here but could one hypothesize that the greater displacement of air in a given volume, the greater the effect of the pattern? Especially if it were constrained to go through a narrower volume port (as it would accelerate in order to do so)
Of course it wouldn't be doing that in a horn as it is ever increasing in volume....
Well here are the pics of recent progress.
The template worked well at first.
Then started to delaminate...
Not completely happy with the results as the edges aren't as crisp as I wanted them to be.
This is caused by my plaster being a bit runny and as I worked the plaster would dry in the template causing less than square openings.
Close up.
I think the idea is good.
The implementation could be improved.
I'll try and see if I can find a sheet of thin plastic at an art store this weekend and cut the pattern out on that.
Et la folie continue...
-andré-
Of course it wouldn't be doing that in a horn as it is ever increasing in volume....
Well here are the pics of recent progress.
An externally hosted image should be here but it was not working when we last tested it.
The template worked well at first.
Then started to delaminate...
Not completely happy with the results as the edges aren't as crisp as I wanted them to be.
This is caused by my plaster being a bit runny and as I worked the plaster would dry in the template causing less than square openings.
Close up.
An externally hosted image should be here but it was not working when we last tested it.
I think the idea is good.
The implementation could be improved.
I'll try and see if I can find a sheet of thin plastic at an art store this weekend and cut the pattern out on that.
Et la folie continue...
-andré-
I wonder if there may be a fortuitous match between good old fashioned non-slip aluminum flooring and EnABLE?
An externally hosted image should be here but it was not working when we last tested it.
G'day Alex (or should I say G'night because it is like 11 pm where you are),
That is interesting that condensing the spacing shifted the effect to lower frequencies. It may be that you had a reduction of the effect in the HF which let you notice the low frequencies more. Or did you actually measure a peak with a mic and freq response software? Applying it to the listening room! Why not?
Regards,
X
G'day X,
It's good morning now for me
Given that the modified pattern was applied to the port of the Voigt pipe I assumed that the bass was being emphasised. I listened in stereo with one side modified and one unchanged. I don't have measuring gear, so it is possible that there was a reduction in HF somehow. I did grab my son's friend and say him down for a listen and asked him what he could hear. He had no idea what I'd done but he said that the side with the modified pattern sounded louder.
Cheers,
Alex
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