"A Flared Port Study" by Jim Moriyasu (1 Viewer)

[Dan M~]

Congrats to Jim on another article in print!
This Months AudioXpress magazine (link to AudioXpress website) contains another article by Jim. Titled ""A Flared Port Study", Jim does a direct comparison of a straight vs. flared port tuned to the same frequency. Impedance curves were checked to confirm the correct tuning and then impedance and SPL measurements were taken at different power levels. The article is a good read and I learned that a flared port must be longer to tune the same as a straight port (I thought it was the other way around :b, but I have never used a flared port).
Jim, if you still read this group, I have some questions to ask. Since large flared ports (4" and larger required for big powerful subs) are difficult if not impossible to find, maybe a study on how much flare is required would be helpful. If I used a straight port with a 1/2, 3/4 or even 1 inch radius routed flare, would that work? Or is an elliptical/parabolic/aerodynamic shape required? Also, what diameter of straight port (if any) would produce the same results as the 3" flared port tested?
Just some thoughts that come to mind. Good article and I recommend it's reading by the DIY community.

 

[Brian Bunge]

Yes, that's a very interesting article. I read it last week, but IIRC the author's conclusion was that he felt that flared ports should be used for any and all ported enclosures.

One thing I found interesting was that he was able to place a flared port within a few inches of a wall without any detrimental effects, whereas the straight port created trouble within several inches from the wall.

Brian

 

[Hank Frankenberg]

Dan, flared ports aren't difficult to find. Here's one source: http://www.psp-inc.com/psp/home6.htm
Parts Express stocks some sizes also.

 

[Dan M~]

Hank-

Yep, looks like they make 3" and 4" sizes (can't tell if they are in stock though). I have come across 4" before but not anything larger. What if 3.5 inch diameter is the best size for your design given box dimensions and port velocity? It would be nice to be able to create what ever size is required. Also, I have concerns with the "thin" ABS/PVC flares, they have been known to break due to screw loading and extreme vibration (as noted in this forum in the past). I would want to add dampening (undercoat?) to the outside of the flares to kill any vibration. A routed flare would not have these problems (any more then a straight flare). But will a simple (relatively small) radius provide the sonic/flow benefits? I don't know.

 

[Hank Frankenberg]

Dan, I have routed my own flares on monitor-size cabinets. I epoxied a straight piece of PVC pipe into the port hole, flush with the outside of the cabinet wall, then used a roundover bit to do the flare. They turned out great - no flange, no screws to bother with. For large cabinets with maximum airflow, you're getting into fluid dynamics and you need the extremely large flare radius that the plastic flares are molded into. I believe the shape of those flares is actually not a circle radius, but asymptotic. If you use dual flared ports, they flow so well that you actually consider the port diameter to be the flare diameter. I'm relying on memory here, but I think that's what Dan Wiggins said in a post a year ago.
Regarding your concern about cracking flare flanges, I haven't seen or heard of that problem. I use good quality black silicon caulk/sealer under the flare flange and down the side of the tube a bit so that there is a good seal. The screws don't need to be tightened very much in order to seal the flare.

 

[Dan M~]

There are some other router bit shapes that may prove more effective then a simple radius (though you can get radii over 1" fairly easy).
Look here for example. The profile looks similar to some flares.
Just providing fuel for those creative fires!

 

[Hank Frankenberg]

Yes, I was considering that -it's called a table edge bit I believe and it does have an increasing radius geometry. Try it.

 

[Brian Bunge]

Another thing mentioned in the article is the little phenomenon where you feel very little airflow from the flared ports as opposed to being able to feel quite a stream of air coming from a non-flared port at a couple of feet away.

I experienced this a few weeks ago when I built a 175L DVC 15" sub with a 4" dual flared port. I was really taken aback when I placed my hand under the port and felt almost no air coming from it! You could blow dry your hair with the air from a non-flared port.

Brian

 

[Anthony_Gomez]

This reminds me of when the 2503 just came out. Scott (from Destiji Engineering) was demoing the 1503 at the bass list meeting. He had the 1503 put into a "garbage barrel enclosre" that had 3 tunning ports (3x 4"...so that you could tune the enclosure using some plumbers plugs...pretty nifty plugs).

well....2000watts, a single non flared port and 14hz later, and we had a "turbine" engine! it was wonderful=)

 

[Brian Bunge]

BTW, the above phenominon is also why you can place the flared port near a wall without getting any chuffing.

Brian