Port Volume Calculation

[matt_martin87 10+ year member]

When subtracting the port volume from the gross volume, do you subtract the extra volume added from end correction (in blue)? Or would you just draw a line straight across where the port physically end for figuring the volume of the port(red line)?

I've been subtracting the blue section from my designs. Please confirm whether this is correct or not.

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[SPLAudioHz 10+ year member]

Subtract from the beginning of your resistance. So draw a line. You can take a router to the edge of your 21 1/2" port entry to lower resistance. you can also run 45 degree strips in all of the corners of the box and rosin the inside as well, but all of that is IMO.

 

[matt_martin87 10+ year member]

I don't think you understood my question or perhaps I didn't word it as well as I should have. Does the port volume extend into the end correction (blue section) or does it only extend to the end of the physical port (red line)?

 

[SPLAudioHz 10+ year member]

I don't think you understood my question or perhaps I didn't word it as well as I should have. Does the port volume extend into the end correction (blue section) or does it only extend to the end of the physical port (red line)?

it only extends to the end of the physical port

 

[matt_martin87 10+ year member]

The difference in tuning is only .3 hz for my application after further calculation. Even so, I would like to know the 100 percent correct way to find it. Thanks for the input SPLAudioHz. I'd still like others to chime in on the subject though. It would be extremely nice to have a scientific explanation to why the port volume doesn't extend into the end correction.

 

[SPLAudioHz 10+ year member]

No prob. Well we need more info to get the proper differential equasion to properly calculate the air flow resistance at the area where the port begins. First year college physics //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[Sarthos 10+ year member]

Lol, if you want a completely scientific explanation about it, you're gonna need to have some rather massive understand of calculus and fluid mechanics. The simple explanation is just that the end correction is just not in the port.

 

[SPLAudioHz 10+ year member]

Lol, if you want a completely scientific explanation about it, you're gonna need to have some rather massive understand of calculus and fluid mechanics. The simple explanation is just that the end correction is just not in the port.

I was actually thinking about attaching pics of the formulas necessary along with how to plug in what numbers, but I lost motivation. Plus calculating it with out the proper measuring divices takes a lot of time. Thhheeeeeennnn recalculating with the subwoofer force of production.................

I like the CAD drawing btw.

 

[ExpoSport 10+ year member]

i was told that end correction gets taken out of gross volume as well. the sub sees that and uses that as port length, not usable airspace. but...that's just what i was told.

 

[RAM_Designs 5,000+ posts]

It's such a small amount that it doesn't even matter anyways. You're talking about less than a tenth of a cube in air space and less than a 1hz change in tuning...you won't be able to tell either way.