Flared Port (1 Viewer)

[Michael R Price]

I think what Jack is trying to say is that the 'mass' of the PR and its air movement have nothing to do with sound quality. In that respect the PR works exactly the same as a port - a mass of air which will resonate at a certain frequency. When it resonates, the pressure it creates damps the movement of the active driver.

I think the only degradation in sound from a PR is because of the notch in response at Fp (is that the abbreviation for its free air resonant frequency?) causing a steeper rolloff and hence more group delay.

The active driver does not push or pull the air through the port/PR. Think of them as two nearly independent systems. Above the resonance point not much happens with the port/PR (think of it as a closed box, right?). Near and at the resonance point, the port/PR gets excited and resonates (on its own). However this air pressure in phase with the active driver causes heavy resistance to its movement.

So why does the port/PR become out of phase with the driver below the tuning frequency? I'm still trying to figure that one out.

Jack, you really know your stuff. I'm learning from it. BTW, that essay by Colin Miller is really something.

 

[Jack Gilvey]

So why does the port/PR become out of phase with the driver below the tuning frequency? I'm still trying to figure that one out.

Basically, below Fb the air starts moving slow enough that the air in the box is capable of rigidly coupling the driver motion to that of the port/PR, so it just acts as a hole in the box, allowing the backwave of the driver to cancel the front.

 

[Brian Bunge]

Jack,

Did you get my email from earlier today? BTW, 'IT' has arrived!!!

Brian

 

[Jack Gilvey]

Haven't been to my hotmail in a while, Brian, I'll try to clear my inbox tomorrow.

 

[Dan M~]

Jack,

I think we are back on the same page!

Reading is good...designing and building is better.

Agreed, but as Colin Miller said, you just can't punch a hole in a box and call it ported! There's some work to do up front.

Thanks again for the help.

 

[Jack Gilvey]

Agreed, but as Colin Miller said, you just can't punch a hole in a box and call it ported!

Didn't say anything like that. My statement would be just the opposite of that. Research is key to successful subs and fulfilling discussions. There's no substitute for designing and building.
Try to do the research and get rid of the notions you've got on how reflex works, many people never do that. Maybe someone can add to this to help, but I can't keep repeating this stuff...have fun.
http://www.lambdacoustics.com/librar...pers/prfaq.htm

 

[Rudy H]

Summing up what Jack said, and PR's as a general whole: Consider them unique ports. They have their own limitations, and benefits, that must be properly addressed in order to be effective.

 

[Bryan Michael]

lets try this agin if you use a bigger port do you need it flaried to be used with a tempest? like a 6 or 8 in port can any one nster my queston?

 

[Rick Thomas]

How does it effect my sub if I add flared ports?I know it increases air speed.But will it lower the bass also?Thanks

 

[Dan M~]

Jack-
My reference to air "spring" came straight from this page:

...above resonance, the greatest force is being applied coincidentally with the almost inconsequential restoring force, countering the momentum it had generated while it was pushing in the other direction. In both cases, though they are phase shifted 180 degrees in relation to each other, there is no significant delay to the response of the swing.

The force is being supplied by the active driver, the "inconsequential" restoring force is the delta in air pressure plus the stiffenes of the surround of the PR and the inertia of it's mass.
Bryan Michael-
I have no experience with the Tempest, so I can not help you. Try contacting Adire directly. They have White papers making suggestions on their site.
Rick Thomas-
The flare manufacturer should give you an "effective length" for the flares. This is needed to adjust the port length for proper tuning. If you create your own flares as discribed earlier, experimentation is in order... I would start by reducing the port length by (1) radius of the flare (assuming it's flared on both ends).
Have a good day...

 

[Jack Gilvey]

Quote:

I can't really do any more in this thread, I've stated what I can. Try "The Loudspeaker Design Cookbook". Once you've designed and built a PR sub, we can get more in-depth.

 

[Rick Thomas]

This is my first sono sub i'v built.I'm very new to all this.

It's a 12"Dayton

I have the tube cut at 16" X 40.5 = 128L. I'm putting a 4" X 16" port in which will give me around 19hz, I think.Now my ? is I picked up some flared pvc ends for a 4" pipe at a flea market.If I put

these on each end what effect will it have on my sub?Should

I cut or lengthen the port or just leave it?Thanks alot

 

[Dan M~]

Jack,

Sorry,

I wrote:

I guess this is the point we disagree on. The active driver DOES control the motion of the PR, not directly coupled to it, but through the "spring" of air in the box. This is how they can be out of phase (at resonance) and in phase (below resonance) per the animated GIF's on the page you refered me to earlier.

My mistake... :b that should read "This is how they can be in phase (at resonance) and out of phase (below resonance) per the animated GIF's on the page you refered me to earlier."

I did not proof properly, I am sorry. I agree that they are in phase at resonance, and only at resonance. On either side of resonance, they are shifting phase as frequency changes (to the point where the PR/port do not move at higher freq's).

I have read TLDC, started with the 3rd printing , skipped the fourth, bought the fifth, skipping the sixth.

Sorry you feel you have nothing more to add... but it's silly to build something unless I understand the tradeoffs needed to make it operate properly. To blindly build someone elses design, I will learn nothing.

I'll let this drop.

Rick Thomas,

If you can locate the manufacturer of your flares, contact them. Are the parts stamped with a name? Generally, a flared port will behave like a longer straight port, tuning wise. A number I have heard tossed around is to reduce the length by 1/2 the flare length. But that would depend on the type of flare. You may have to experiment some. I think Patrick Sun did some experimenting with a variable port length on one of his designs. That might give you some guidance. I may be wrong (not the first time...), hopefully someone else will chime in and help.

Good luck.

 

[Jack Gilvey]

...it's silly to build something unless I understand the tradeoffs needed to make it operate properly. To blindly build someone elses design, I will learn nothing.

Absolutely. Learn the concepts correctly, design , then build. Best of luck with the project.