Flared Port (1 Viewer)

[Rick Thomas]

I'm going to be putting a 4" port in my sono sub.What should I use for the port and where do i get something flared for the ends thanks.

 

[jeff lam]

If you want flared ends you will need the kit. Partsexpress, madisound, adire audio all have them.

Or you can just use a straight 4" PVC pipe. But the flared ends would be required if you had a Shiva, Tempest, or similar driver.

 

[Rick Thomas]

Do i need the port flared on both ends or just the end inside the sono?thanks

 

[Dan M~]

Poor Mans flare...

Cut your PVC to length, glue/insert into a laminated scrap of MDF (1.5" thick)that has a hole cut to the right size, use router roundover bit with guide bearing to roundover ID of tube/MDF, cut OD of MDF round and use roundover bit around the outside of MDF. Experiment to find out what size of OD works best. Roundover bits can be found up to 3" radius (to much for handheld router, works with large router/shaper table though, also big bucks$$$$!!!) but a 1/2" radius looks good and gives a full 1" diameter lip to your port. Install tube in cabinet and rout mouth there...

Hope that makes some sense... experiment and see what you can do.

Good luck

 

[Jack Gilvey]

Do i need the port flared on both ends or just the end inside the sono?thanks

In order for "flared ports" to have appreciable effect, they should be at both ends and should be large flares such as those seen on the aeroports. You can achieve a flare of sorts with a roundover, but to replicate the kind of flare I'm speaking of would require a monster bit and probably an endcap 5" thick.

 

[Dan M~]

Keeping with the poor mans ideas...

If your air flow is sub sonic (

 

[Jack Gilvey]

I've read about attempts at applying such techniques, the "dimpling" of the B&W ports come to mind. Being derived from D/C fluid dynamics, I don't know how well they apply to an A/C system like ports used as Helmholtz resonators. In the end, there seems no replacement for a well-flared port to reduce turbulence across the mouth, which is the main reason behind compression and noise. Any flare is better than none, though.

 

[Dan M~]

Jack,
Good point. A/c air movement would consist of air moving in one direction, stopping and then accelerating in the other direction, repeat until the music stops. The average airspeed will be zero!
The actual peak speed is the point of concern. Do the design programs that report port speed give an acurate number? I wonder what accounting do they take for "drag" within the port? The hard answer is to have as large a port as possible (length being the usual limiting factor) and ad some flare. The simple answer is "closed box".
Have fun.

 

[Jack Gilvey]

The hard answer is to have as large a port as possible (length being the usual limiting factor) and ad some flare.

I suppose it is a bit of a "brute-force" solution, but it seems the right one. I think that particular wheel has been reinvented a few times. Even very large ports,though, exhibit signs of compression at surprizingly low levels (See Dickason, LDC 5th Ed, also this article ). And they are of limited utility with modern drivers which have very small box requirments, yet can move prodigious amopunts of air. This is one reason I've become interested in passive radiators of late, they bypass these problems.

 

[Dan M~]

This is one reason I've become interested in passive radiators of late, they bypass these problems.

You may get rid of the port noise, but you add mass to the system (diaphragms and "added mass" to tune the PR's) that need to be controlled. So you have one driver motor controlling the mass of 2 or three cones! Outside the harmonic resonance of the PR's, the motor is fighting the extra mass at the same time it is trying to control it's own enertia. I do not know all the facts, but I think that there are a few challenges even with PR's.

As you have said before "There's no free lunch", or something similar!

Keep up the good work.

 

[Brian Bunge]

You may get rid of the port noise, but you add mass to the system (diaphragms and "added mass" to tune the PR's) that need to be controlled. So you have one driver motor controlling the mass of 2 or three cones! Outside the harmonic resonance of the PR's, the motor is fighting the extra mass at the same time it is trying to control it's own enertia. I do not know all the facts, but I think that there are a few challenges even with PR's.

Could this be why PR subs are said to have poorer transient response than their ported counterparts?

Brian

 

[Rudy H]

Dont forget that the air inside the ports has weight as well..... that's how longer ports tune to lower frequencies.

An "ideal" PR would probably be one that has a very very soft suspension, SQ wise that is.

 

[Jack Gilvey]

An "ideal" PR would probably be one that has a very very soft suspension, SQ wise that is.

Yep, that's when they act closest to an "ideal" reflex system. That's why I like the Lambdas, and part of why they used to be considered the pre-eminent PR's.

 

[Dan M~]

Jack,

Thanks for the link. I printed it out and will sit down and study it.

With respect to PR's and moving mass... The PR's move a mass of air too. How much compared to a ported system, I do not know. When the driver moves, it displaces air. On a sealed system, the air compresses and acts like a spring to help the cone recover. In a ported system the air is compressed and pushed out the port, the driver must "suck" the air back through the port to return to it's starting position (There is some residual "spring" pressure within the box to help). In a PR system the air compresses and moves the PR's out (displacing air outside the box). The PR's provide some help in recovery, as they want to return to the starting position too.

I need to study this somemore.

P.S. Rick Thomas, sorry for hi-jacking your thread.

Happy Easter/Passover.

 

[Jack Gilvey]

In a ported system the air is compressed and pushed out the port, the driver must "suck" the air back through the port to return to it's starting position (There is some residual "spring" pressure within the box to help). In a PR system the air compresses and moves the PR's out (displacing air outside the box). The PR's provide some help in recovery, as they want to return to the starting position too.

This is not what happens, but I think the misconceptions are common. The driver does not "push air out the port", nor does it directly displace the PR's, or push them out and suck them back in. In a reflex system, the port/PR resonate so much at Fb that the pressure they create damps the motion of the driver. That article illustrates it nicely.

In addition, the heavier the Mms of the PR the better it sounds, in general, since the free air resonance is pushed further down in frequency, thereby pushing the PR notch/group delay further out of the passband.

 

[Dan M~]

Hi Jack,
Yes my discription was VERY simplified, but you do have moving air. Push in on your driver and the air moves out of the port or your PR's move out, pushing air.

In a reflex system, the port/PR resonate so much at Fb that the pressure they create damps the motion of the driver.

Yes.. only at the resonance frequency and you only have that (by itself) if you are playing a sine wave of that freq. Generaly the driver is always moving, creating waves of air pressure/sound pressure.
I admitt that I'm in over my head when discussing this stuff, I've got some reading to do. Thanks for the link and I'm sure I'll be back to pick your brain some more!

 

[Jack Gilvey]

Yes.. only at the resonance frequency and you only have that (by itself) if you are playing a sine wave of that freq. Generaly the driver is always moving, creating waves of air pressure/sound pressure.

I'm familar with reflex theory, my point was that the actual process was the opposite of what you describe. The driver isn't pushing in as the PR's move out..that would be out-of-phase. At the PR's greatest resonance, thay actually move more or less in tandem, and that very pressure almost stops the woofer.

Please read that article.

 

[Bryan Michael]

if you use a bigger port do you need it flaried to be used with a tempest? like a 6 or 8 in port

 

[Bryan Michael]

if you use a bigger port do you need it flaried to be used with a tempest? like a 6 or 8 in port

 

[Dan M~]

Jack said-

Also, a large volume of air pushed through a relatively small opening may generate turbulence, or a chuffing sound. Ports can be shaped (flared at the openings) to limit turbulence, however, so the compromise doesn’t have to arise, but must be dealt with. Passive radiators don’t suffer from that problem at all but, unlike ports, they do have excursion limitations.

Maybe we are misunderstanding each other. From your linked paper and using the animated GIF's(?) as a basis, this is how I understand how the system works:
Case 1- Above the port/PR's resonance, little or no air moves thru the port/moves the PR. The active driver moves as needed.
Case 2- At the port/PR resonance, LOTS of air moves thru the port/moves the PR. And the active driver moves very little as the internal pressure waves work against the drivers movement. (The driver is exciting the system without moving... cool stuff!)
Case 3- Below the port/PR resonance, lots of air moves thru the port/moves the PR, but it is out of phase and cancels the active drivers output (acting like an open box). The driver is unsupported and can bottom out.
Since ALL energy is being introduced into the system only by the active driver, at port/PR resonance the driver is moving the air through the port or moving the PR (and associated air). In or out of phase does not matter to make my point. On a ported system the active driver must push, and pull, the air through the port. In a PR system, the suspension helps to restore the PR diaphragm to the zero point. That may be why you find the PR system sounds better. I still feel that the enertia of the PR/mass and the air the PR moves degrades the sound quality, makes the system "sloppy". Thats an unfair word to use as I have only listened to one PR system and I can say that it did not sound sloppy! The answer is to use closed systems and live with the resulting box size to achieve the output... not a popular idea around my house. I need to study PR's some more and listen to a few more to really see what they can do.
Like I've said, I've got a lot to learn, thanks for the help.