Air velocity in flared ports (1 Viewer)

[PeterOS]

Just doing a bit of research here on flared ports and have my hands on some decent software in college (a few of ye have mentioned it before I think, ALGOR). I have done a few analyses on 3” ports with no flare, 30mm, 40mm, 50mm and 60mm radius flares.

I used a frequency of 16Hz since this would be where the airflow would be relatively large, approx 25m/s for my 17” dual 3” ports.
Here are the basic results. The velocities are the max reached which are at full excursion of the driver (Tempest in a 170L approx enclosure).
The 0.0156sec is the time taken for the tempest to start from rest and go to positive Xmax. It then goes to full negative Xmax after 0.0468sec. (just to let ye know where the numbers came from)

Time----------0.0156sec-----------0.0468

No flare--------(63m/s)----------(-61m/s)

30mm flare------(118m/s)---------(-125m/s)

40mm flare------(98m/s)----------(-104m/s)

50mm flare------(115m/s)---------(-113m/s)

60mm flare------(98.8m/s)--------(-104.3m/s)

Looking straight off from the chart a 30mm flared radius looks the best. I will look into radii more closely from 25mm to 35mm.
If ye want to have a look at the avi files I made, here is the link. They are all about 3Meg each though.
http://uk.briefcase.yahoo.com/pos143
Then click on ALGOR album

Could anyone tell me what the flare radius on the Parts Express percision port is? (It just for analyses, I aint going to try to rip them off..... then again


Since I am posting, I just done a few measurements i took @1m distance from a sealed 160L enclosed tempest. Running the PE 250watt plate amp at full whack, I got these results using the Radio Shack SPL and the correction values...

FREQ----RAW SPL---SPL(corrected)
16--------97----------108.5
18--------101---------109.0
20--------104---------111.5
22--------104---------110.5
25--------107---------112.0
28--------107---------111.0
31.5------109---------112.0
36--------113---------115.5
40--------115---------117.5
45--------117---------119.0
50--------117---------118.5
56--------118---------119.5
63--------118---------119.5
71--------118---------119.5
80--------118---------119.5
89--------118---------119.5
100-------118---------120.0
111-------119---------120.0
125-------119---------119.5
142.5-----118---------118.5
160-------119---------118.5

Don't they look a bit over the top for not even being inside a room!!!

 

[Chris Tsutsui]

2 words, passive radiator.

jk, nice work. I have some 3" precision ports but they are in my sub right now. :frowning:

I cna't believe you measured your tempest at 120db, were you wearing ear plugs?

What if you played with the surface of the ports like B&W and made dimples like a golf ball. Or what if you shaped the ports like turbines so it creates a vortex? What if there was a single 90deg bend in a port... Do the sims allow stuff like that? The people want to know.

 

[Hank Frankenberg]

Why analyze theoretical port radii? There are only a couple of sources of good flared ports and they have fixed radii. If one of the theoretical radii look better than what's commercially available, are you going to make your own?

 

[PeterOS]

Hi Chris,
As you asked there, I wasn't even wearing ear plugs ( a bit stupid) but since is was out side it didn't seem to be that loud. Inside a room I can get everything to vibrate so at least I know there is a fair bit of power there. I still think that the SPL readings I got sound a bit OTT.

You mentioned dimpling the surface of the port, something I was thinking of doing but would of been very difficult to draw up in SolidWorks.
Bends in ports, as you can expect, cause alot of turbulance and a big no no. I don't have any analyses done on bends in ports though. I might when I am finished this project.
I think the link I gave to my Yahoo Briefcase won't let any of the public view it. Thats good in a way since the stuff I posted there were very low in detail i.e. analysis detail not video resolution. I will post the new ones when I get them done.

Hank,
I know this has been done before but for purpose of my project in college I have to do it. When I find out the radius giving the best predicted results, I will make that one. I will make the shape on a CNC that allows me to form the port tube around it to give it a flare (heat needed of course to soften the plastic).

 

[Isaac C]

Peter, did you get a chance to look at that AES Preprint about flared ports? If not, you might be interested to know that the same text was re-released last year, so you no longer have to pay for the preprint just to study the article (that is if your local library has a JAES subscription). Here it is again:

Maximizing Performance from Loudspeaker Ports

Vol. 50, Number 1 pp. 19 (2002)
Author: Alex Salvatti
Author: Allan Devantier
Author: Doug J. Button

Abstract: There is a current trend in the marketplace for loudspeaker ports to have a more aerodynamic appearance. While this may be as much for appearance as for performance reasons, the sharp discontinuity at the end of a traditional port does create turbulence which negatively affects most performance parameters. Ports altered to provide a more aerodynamic shape to minimize turbulence for both the inlet and the exit air streams show performance improvements in efficiency, acoustic compression, maximum output, and distortion reduction. The ideal port shapes for high-velocity inlet and exit air streams are different, and the best solution is one that balances both. In addition turbulence is actually preferred in matters of cooling the box through heat exchange via the air in the port.

-- from http://www.aes.org/journal/search.html


Good luck with your project

Isaac

(Thanks again Janne for the heads up on the article.)