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Discussion Starter #1
Hey Guys, been a while since I've roamed the forums. Hope everyone is doing well with all that is happening in the world today.

I need some help please from more experienced guys than myself with a ported enclosure design. The sub in question is an AudioFrog GB12 D2. I am going to be using a 4-inch precision port. I build plan I have come up with by doing some modelling in WinISD is 1.9 ft3 tuned to 30Hz. New the thing I can't seem to figure out is the port length; let me break it down:

  • As per WinISD under the 'vents' tab when left at default end correction (0.732), the port length I get is 16.98 inches
  • As per WinISD again, if I change the end correction to two flanged ends, the port length is 16.53 inches
  • As per Precision Port's website, the port length should be flare length port required (17.87844) minus 6 inches which is 11.87844 inches

Now the difference between 16.53 inches and 11.87 inches is a big deal. Can someone shed some light on this please and what would be the correct length to use in this case?
 

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16.5 vs 17.8
The flares are +3" on each end so the physical length is still there it's just the port tube in the middle of the flares that's 11". Flared ports don't change tuning frequency they only smooth out air flow. They are longer because only half the flare affects the tuning.

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Discussion Starter #3
Thank you Daloudin! I guess the wording on their website made it a little difficult to understand lol. Makes sense now.

Another question if you don't mind. How do you calculate the volume displaced by the precision port? Would you use V = Pie R squared x H or another method that accounts for the flared ends?
 

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You can calculate volume of the flare separately but it's not enough difference to matter unless you're doing a huge (10" +) port.

But if you're really into calculus you can Google "Volume of a Solid of Revolution" to explain the calculation below:


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I tried figuring out a way to get a 4" flared port to fit inside a 1.5 cuft box when i had my GB12 and could not make it fit. I ended up going slot port.
 

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Also, even with an aeroport 4" is a little on the high side for port velocity - try the slot port - it's a lot more forgiving.
 

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Discussion Starter #7
Thanks for all the input guys. I was planning to use an elbow in the port so I don't think fitment of the port in the box would be an issue. I planned to put the port on the same face as the sub and internally a brace/support would hold the port at the other end.

I abandoned the idea of using a slot port because the overall size of the enclosure would be much bigger using a slot port vs a round port. JCsAudio used a precision port in his ported AF GB12 enclosure and it seemed to work out well for him, I don't recall seeing any issues with port velocity that he had mentioned.
 

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Thanks for all the input guys. I was planning to use an elbow in the port so I don't think fitment of the port in the box would be an issue. I planned to put the port on the same face as the sub and internally a brace/support would hold the port at the other end.

I abandoned the idea of using a slot port because the overall size of the enclosure would be much bigger using a slot port vs a round port. JCsAudio used a precision port in his ported AF GB12 enclosure and it seemed to work out well for him, I don't recall seeing any issues with port velocity that he had mentioned.
flared ports do not make the box smaller.
 

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Discussion Starter #9 (Edited)
I was referring to the displacement of a slot port vs a round port. The displacement of a slot port is typically more than a round port no?

When you factor that in, the overall box will be bigger for a slot port design to give an internal usable volume of 1.9 ft3 after you minus driver, brace and port displacement.
 

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I was referring to the displacement of a slot port vs a round port. The displacement of a slot port is typically more than a round port no?

When you factor that in, the overall box will be bigger for a slot port design to give an internal usable volume of 1.9 ft3 after you minus driver, brace and port displacement.
For me its always been a push. Yes sometimes the box could get a couple inches wider with a slot port, but its always been easier for me to locate a slot port vs a round port in small boxes like this one. But if you can fit that giant flair inside the box go for it. I never could.
 

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Discussion Starter #11
Yeh man, I'll give it a goo!

Also, I've 'discovered' today that the flared ends are 3 inches (what Daloudin said) BUT the usable length of each flared end is actually 2.5 inches, not 1.5 inches. So it all makes more sense to me now:

11.878 + 5 = 16.878 inches which is much closer to what I was getting in WinISD (16.53).
 

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I was referring to the displacement of a slot port vs a round port. The displacement of a slot port is typically more than a round port no?

When you factor that in, the overall box will be bigger for a slot port design to give an internal usable volume of 1.9 ft3 after you minus driver, brace and port displacement.
Typically yes because the port wall is usually made out of the same material as the rest of the box versus pvc wall thickness. But if you're really trying to minimize box volume can you make room for a PR (or 2?)

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Discussion Starter #13
Also trying to keep my cost down at the moment cuz we are expecting munchkin #2. The first one is almost 2 years old.

I have literally everything I need to build the ported box except a PVC elbow and PVC glue. To go PR, I'd have to buy the PR(s) and wifey won't be too happy about that right now haha.

She's already told me if I could put speakers in every room in the house including the bathroom I would 😈
 

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Sounds good - please update this thread with your results and impressions - we all love a happy ending.
 

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Discussion Starter #15
Hahaha, for sure I will......I had promised a build log for some time now and I just haven't gotten the time to sort out the pics yet.....in the meantime, here are some pics of the amp rack I built. Enjoy and comment
1.jpg
2.jpg
3.jpg
!
 

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You can calculate volume of the flare separately but it's not enough difference to matter unless you're doing a huge (10" +) port.

But if you're really into calculus you can Google "Volume of a Solid of Revolution" to explain the calculation below:


Sent from my SM-G965U using Tapatalk
For those not samiliar with Liebniz or Newton's work, using water and measuring cup is a real thing.
 

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Discussion Starter #17
Great idea Holmz! Didn't even think of that........brings me back to my school days with physics/chemistry experiments in the lab.
 

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Just curious if you differed in box/port size from what AF recommends in their user manual. I have a GB10D2 and was planning on just using their recommendations.

Patrick
 

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Discussion Starter #19
Hey Patrick03, for the GB12 as per AudioFrog's manual, the recommended ported box size is 1.5 ft3 tuned to 33Hz using a 4 inch round port. The modelling I did also uses a 4 inch round port but I played around a bit with enclosure size and tuning. I came up with 1.9 ft3 tuned to 30Hz. Between the 2, the 1.9 ft3 has slightly more output 40Hz and down and the 1.5 ft3 has slightly more output 40Hz and up.

Manufacturer's suggestions for enclosure sizes are typically an overall good solution that would satisfy most people. There is nothing wrong with experimenting a bit to see how different enclosure sizes and tuning affect the response of the sub. There is also nothing wrong with sticking to what AF recommended. If you are building the enclosure yourself and are relatively new at building stuff, I would recommend trying what the user manual says first as all measurements are laid out for you so it takes the guess-work out of the build.
 

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Hey Guys, been a while since I've roamed the forums. Hope everyone is doing well with all that is happening in the world today.

I need some help please from more experienced guys than myself with a ported enclosure design. The sub in question is an AudioFrog GB12 D2. I am going to be using a 4-inch precision port. I build plan I have come up with by doing some modelling in WinISD is 1.9 ft3 tuned to 30Hz. New the thing I can't seem to figure out is the port length; let me break it down:

  • As per WinISD under the 'vents' tab when left at default end correction (0.732), the port length I get is 16.98 inches
  • As per WinISD again, if I change the end correction to two flanged ends, the port length is 16.53 inches
  • As per Precision Port's website, the port length should be flare length port required (17.87844) minus 6 inches which is 11.87844 inches

Now the difference between 16.53 inches and 11.87 inches is a big deal. Can someone shed some light on this please and what would be the correct length to use in this case?
If you want to tune a port very accurately, then you just need to have a measuring circuit. It is not at all difficult to collect and use REW. Only by measuring do you have a chance to tune the port to within 1 hertz. There are simply no other options. The calculation in the program gives only approximate data.
 
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