This paper cites a manufacturer who did use dimples as on a golf ball but then it goes on to show that glass beads attached to the walls has no benefit. It looks like there's no empirical data specifically focused on the effect of actual dimples.
Dimples or bumps both make for more turbulent air flow, which is not a good thing in bass reflex port design.
The aerodynamic features that make dimpled golf balls fly further are not useful in bass reflex ports.
That said, nothing to stop you if you'd like to focus on empirical data specifically around the effect of actual dimples in ports. DIY!
Art
My understanding with golf balls is that the dimples cause low level turbulence close to the balls surface making airflow over that turbulence much smoother. Similar to model yachts being sanded sideways rather than long ways. It makes sense in my head. Will try and follow up with a picture after work.
It's curious why they wouldn't replicate the example they refer to. Do you have evidence to verify your statement?
In "Maximizing Performance from Loudspeaker Ports" their Study #7 roughness experiments used roughness ratios ranging from approximately 0.01 to 0.042 on the Moody chart, using precision glass beads of various sizes ranging from 1mm to 2.5mm to the inside port walls using a spray adhesive.
Creating dimples on the inside of a port to replicate the same roughness ratio range would have been far more difficult to achieve.
Evidence that "a turbulent air flow is not a good thing in bass reflex port design" can be gathered from their Study#2
ort Compression vs. Reynold’s number, Study #4: Acoustic Compression, and leads to their first conclusion:1) Vast historical data and results herein suggest that the largest port area allowable by your design should be employed to keep air velocity down if low port compression and low distortion are desired. This is, however, in conflict with the solution for best heat exchange in the box.Like everything in life, one has to weigh the compromises- port compression due to excessive air velocities, or power compression due to less heat exchange...
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Large vents placed near the top and bottom of the box (like a large shelf vent, for example), seems like the best solution - cooling will be done by simple convection and port compression should be low. Interesting enough I have a 4th/6th order BP config with exactly that type of arrangement. It's never left the design stage though.
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