Yes, they call it a 'flowport'.
While aerodynamic benefits are real from a dimpled port, they really only come into effect at higher velocities. So basically if your speaker has a port that is a bit small, it may help but really just use a bigger port(of course pipe organ resonance etc needs to be taken into account)
A large enough port with smooth flared ends will have no audible port noise.
Doubtful. We aren't talking much velocity here, and also like most manufacturers, B&W were looking for a way to differentiate their products and make them special.
How many different port shapes are out there with each manufacturer claiming their own version is superior (dimpled, oval, slot, multiple ports, port curves etc etc).
Surely if you combined a flared, oval, dimpled, variable geometry port you'd have some sort of SUPER SPEAKER with magic bass that changes the world and distorts time-space? No?
Can't say I've ever hear anyone mention how amazing their port sounds...
hey
As well as the lengthy discussion on here before, there is also a white paper you can download on port design. While it primarily deals with elliptical ports and end correction, and how these factors affect airflow in the ports and at the transition into free air, they also have measurements about textured ports. IIRC it showed that it both decreased SPL and increased THD, and was not beneficial.
http://jahonen.kapsi.fi/Audio/Papers/AES_PortPaper.pdf
As well as the lengthy discussion on here before, there is also a white paper you can download on port design. While it primarily deals with elliptical ports and end correction, and how these factors affect airflow in the ports and at the transition into free air, they also have measurements about textured ports. IIRC it showed that it both decreased SPL and increased THD, and was not beneficial.
http://jahonen.kapsi.fi/Audio/Papers/AES_PortPaper.pdf
As mentioned (and linked) in post #11 by kevinmcdonough, it was tried and found to not be effective, as described in pages 38-39 of this 2002 A.E.S. White paper. Emphasis in bold is mine.
"Maximizing Performance from Loudspeaker Ports
By
ALEX SALVATTI,(JBL Professional) AES Member, ALLAN DEVANTIER,(Infinity Systems), AND DOUG J. BUTTON(JBL Professional), AES Member
3.7 Roughness Experiment
One might think that smoother surface textures in ports would directly result in higher performance. However, since Coulomb’s experiments in the 1800s it has been known that the surface roughness has an effect on friction resistance. Interestingly, the effect is negligible in laminar flow, but not if the flow is turbulent, that is, surface roughness effects would be evident only at the higher port velocities. If reduced drag is desired, a rough surface will actually perform better due to boundary-layer effects. This is the reason why golf balls have dimples—the surface roughness is intended to “trip” the boundary layer so that it will go turbulent at a lower Reynolds number (in flight the Re of gold balls is about 100 000). The turbulence causes the separation point to move from the front to the back of the golf ball, thereby reducing drag and allowing a farther flight. There are now even commercially available subwoofer loudspeakers that use a flared port with dimples, similar to a golf ball....To test the hypothesis, we constructed five copies of the best performing port (NFR = 0.5) and then affixed precision glass beads of various sizes, ranging from 1 to 2.5 mm, to the inside port walls using a spray adhesive. This corresponds to a roughness ratio range of approximately 0.02 – 0.04. These ports were manufactured such that the volume occupied by the beads was accounted for. The ports were then subjected to the same distortion and compression tests described ear- lier. Contrary to expectation, over the range of roughness examined, rough ports were generally inferior to the smooth-walled port. Rough ports had more harmonic distortion above 95 dB at 1 m. Only in a very narrow range, between 90 and 95 dB, did the wall roughness produce a marginal improvement in odd harmonic distortion. At all other levels the smooth-walled port performed better (Fig. 46).
Based on the fluid mechanics literature [18], we expected to see a benefit in rough walls in the acoustic compression measurement. Unfortunately, roughened port walls failed to show any advantages here as well. In fact, Fig. 47 shows that all rough ports were consistently compressing about 1–1.5 dB more than the smooth port. These negative results may be explained by noting that even at the highest Reynolds numbers near 100 000, the Moody chart predicts that we are only just entering the transition region and have not reached the fully turbulent region where roughness would be expected to make a large impact. Based on these results, it does not appear that dimpling the walls guarantees any extra performance."
Their 18 year old study covered a lot of ground!
Art
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I use WD-40 on mine.
Seriously, I can't think it would be measurable with the air movement we are talking here.
But raised bumps are not the same as dimples. Has their effect been shown to be similar? Golf ball history suggests the change from raised bumps to dimples was a major improvement cited by Bobby Jones.
Numerical study of the aerodynamics of sound sources in a bass-reflex port (2017)
Try vortex generators. They're easy to mock up with painter's tape.
Try vortex generators. They're easy to mock up with painter's tape.
That’s exactly what I thought.
The JBL paper has a lot of information in it but I wondered how they missed that.
Barry.
JBL published a paper that was fairly obsessive about the ideal port shape:
http://jahonen.kapsi.fi/Audio/Papers/AES_PortPaper.pdf
Up until I read this, I did not know that port shape affected distortion.
http://jahonen.kapsi.fi/Audio/Papers/AES_PortPaper.pdf
Up until I read this, I did not know that port shape affected distortion.
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