Adapting Port Sizes

[Ryan S]

So it happened... my trunk's electronic lock mechanism failed, and I had to spend 3hrs carefully removing all my audio stuff to get to my trunk. I never want to go through that again (plus I couldn't get out my spare tire with my old box anyways).

I'm redoing my setup (sacrificing some SQ) to make it more economical. I'm building my two 12'' Type-R's into my spare tire well (ported) so I can ditch my external box.

A couple questions:

Alpine calls for a Vent Displacement of 0.305ft^3 and then it lists the Vent Area/Length.

Since I don't have the room for the traditional square vent Alpine gives specs to build, I'm planning on using cylindrical vents. Is it just as simple as adapting the displacement to that of my cylindrical vents? I've only got a 12'' depth to work with...

Click to read more...

 

[tcguy85 10+ year member]

use the aero ports from parts express.... or use pvc from home depot and make your own.

 

[audioholic 5,000+ posts]

It should require less port area going from square ports to round ports. Will save you some space there. You could also consider external ports to save mmore enclosure space.

 

[tcguy85 10+ year member]

YEAH! external aeros FTMFW!! lol

 

[Ryan S]

I'll have an internal volume of 1.64ft^3 per sub, which is what Alpine calls ideal for ported.

I was planning using PVC for my ports, just needed to clarify I could change the port shape without adversely affecting sound too much and how to calculate it...because if each sub requires a displacement of .305ft^5, I would need six(6) PVC ports that are 3'' in diameter and at a 12'' length. //content.invisioncic.com/y282845/emoticons/eek.gif.771b7a90cf45cabdc554ff1121c21c4a.gif

Unless my math is wrong? Can anyone help? //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

Here's what Alpine says for a vented box (I can only go 12'' long per port):

 

[tcguy85 10+ year member]

don't worry about it so much. you just need to keep the tuning at the number you want and have the 15 square inches of port area that they recommend. one 4inch round aero port might be enough per sub. it'll be just under the 15 square feet they recommend though.

 

[Ryan S]

Yeah, I was thinking a 4'' dia. port was probably the direction I'd have to travel. My end project will look something similiar to this (this is hatchback GTI, mine is sedan Jetta), but slightly more 'clean':

Perhaps for ports I'll use two clear acrylic tubes going upwards from my subs through the rear deck and into the cabin? Illuminated blue of course. //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

 

[audioholic 5,000+ posts]

Only bad thing about port 'smoke stacks' imo is the phase problems it causes.

 

[tcguy85 10+ year member]

Only bad thing about port 'smoke stacks' imo is the phase problems it causes.

explain further please.

my design has phase problems?

 

[audioholic 5,000+ posts]

explain further please.
my design has phase problems?

Group delay.

 

[IgnoreMe 5,000+ posts]

if you want to cut down port area you will need flared ports. the flare is what counts //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif. that flare lets you get away with a lot more constraints.

regular round pvc wont be TOO much different from a efficient slot port (not tall and narrow etc)

 

[tcguy85 10+ year member]

if you want to cut down port area you will need flared ports. the flare is what counts //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif. that flare lets you get away with a lot more constraints.
regular round pvc wont be TOO much different from a efficient slot port (not tall and narrow etc)

o rly?

 

[IgnoreMe 5,000+ posts]

o rly?

yup. using a 1" radius flare results in about a 50% reduction in vent velocity. psp ports use about a 1" flare IIRC.

dont get me wrong though. round ports are more efficient than slots, because there are no corners, and the there is minimal contact between the air and the perimeter of the port. think about a 4x4" port and a 2x8". both add up to 16^2" of port, however one has 16" of contact with the air (4x4 port) and the other has 20" of perimeter thats in contact with the port air.

rounds ports and slots aren't exactly equal, but they also dont compare to the efficiency of a flared aero port either.

 

[tcguy85 10+ year member]

yup. using a 1" radius flare results in about a 50% reduction in vent velocity. psp ports use about a 1" flare IIRC.
dont get me wrong though. round ports are more efficient than slots, because there are no corners, and the there is minimal contact between the air and the perimeter of the port. think about a 4x4" port and a 2x8". both add up to 16^2" of port, however one has 16" of contact with the air (4x4 port) and the other has 20" of perimeter thats in contact with the port air.

rounds ports and slots aren't exactly equal, but they also dont compare to the efficiency of a flared aero port either.

interesting. thats why my 3 round inch port has very little port noise. it does have 2 bends in it, but i used a big flare on each end. i was really concerned about port noise before i tried it and was wondering why it works so well.

thanks man! that cleared it up quite a bit.

edit: i'm also just wondering where you got this info. i'd like to read even more on it if possible. thanks.