Precision Ports Lenght ?

Hello
I am building the Adrire Alignment Design Ported Subwoofer .
It calls for cutting the 3" flared port center tube 11" long .
When reading the installation Process for The Precision Port Kits
I get lost .
Does anybody have any experience with these ports and how to calculate the length ?

Link to ports 3" Precision Ports

Thanks for any Help

General rule of thumb: the calculated length using 1/3 the radius of the flair (bell) of the vent.

Best Regards,
TerryO
 
Just a recap as perhaps it isn't entirely clear. If you have a port length of 11 inches and it's flaired on the outside then the calculations have to account for the added length provided by the flair itself. If the total length is 11 inches and the radius of the flair is 3/4 inch, then the flair provides a nominal length of 1/4 inch, in which case the tube would be 10 3/4 inches.

If, OTOH, you are using a flaired bell at both ends of the port, and assuming that they both have a 3/4 inch radiuses flair then, the flairs account for 1/2 inch of the total length and the tube would be cut accordingly.

The best proceedure is to assemble the port "dry" outside the enclosure, measure the "assembled" port with a ruler or tape and then, based on the radius of the port's flair, you subtract the necessary amount from the total and cut off the excess. In the case of the hypothetical 3/4 inch flair at one end you would add 1/2 inch to the designed total, in this case it would be cut off at 11 1/2 inches.

I hope this makes sense.

Best Regards,
TerryO
 
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Yeah, what he said. Kinda.

Measure the straight part. Then, add 1/3 (some say 1/2) of the radiused length.

If the straight part were 10" and the end-to-end length were 16" then the radiused parts are (16-10=) 6" long.
So you would add 2"-3" (1/3 to 1/2 of the 6") and get an effective total length of
12"-13"

Then assemble the whole box, test, and find that after all your careful design work, the port frequency is different from the predicted anyway.

--> Always make the port longer and trimmable!

P.S. But what you state about the instructions is also not clear to me. Could you quote the instructions exactly? Seems like maybe they're already allowing for the port flare...
 
I'll second the idea of seeing the instructions.
Evidently I wasn't too clear on this, but the total length is measured with the flaired part in place. Just place it with the flaired bell down on a tabletop, then run a ruler down until it touches. This is your overall length. Now, if the radius of the flair is 3/4 inch, only 1/4 inch of the radius is actually contributing to the calculated length. Therefore, you would (for an 11 inch port) mark the end of the upended tube at 11 1/2 inches and cut there. It's a lot harder to explain than the actual operation.
:D

Best Regards,
TerryO
 

Fleabor

Member
2010-09-28 11:07 pm
Thanks for all the help . I will write out the instructions


8466.4R2
LV= _____________ -1.463R

(Vb)Fb 2

Lv=port length in inches
Vb= volume of box in cubic feet
Fb=tuning frequency
R= radius of port (1/2 of port diameter )

2) Trim center tube to 5" shorter than LV from step one.
3) The Precision Port should be 1" longer than LV when assembled


I hope that might help .
The Adire Alignment Designs is a 214L Cabinet tuned to 15.4 Hz
with 64 ounces of polyfill .
In the instructions says to cut the Flared port kits with 11" long center tube . So I am thinking that they already did all the math and making it simple and just telling you to cut center tubes to 11" long for best results .
Well any more help would be great
Thanks
 
This is an Adire alignment, as stated above the tube in the kit is 12" long, cut 1" off the length. Disregard the other posts as they didn't understand the specific instructions which were:

It calls for cutting the 3" flared port center tube 11" long .

Cut the center tube to 11", glue on the flares to each end and install the port.
 
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This is an Adire alignment, as stated above the tube in the kit is 12" long, cut 1" off the length. Disregard the other posts as they didn't understand the specific instructions which were:

It calls for cutting the 3" flared port center tube 11" long .

Cut the center tube to 11", glue on the flares to each end and install the port.

You're correct in that the instructions call for actually cutting the center tube to 11 inches and I somehow mistakenly believed that it called for "a vent tube 11 inches long". I apologize for overlooking what I should have easily noticed.
:eek:

So, the OP should cut it at 11 inches.

However, my earlier posts are the way that, unless otherwise specified, the length of a flaired port is calculated.

Best Regards,
TerryO