Port Enclosure Design

[Jeremy Coc]

Did some searching on the forums before asking these questions but didn't really find exactly the answers I was after.

If I didn't search hard enough feel free to post links to other threads I'd be happy to have a read if it's been discussed before

Purchasing other equipment that is 'better' isn't an option due to cash and location issues so I'll give you the details of what I've got

I have a Orion HCCA 15.2, rated at 2000wrms that I will be powering with a Hifonics Brutus BXI2610D @1ohm 2600wrms

I plan to build a 4.5~ cuft box to fit in the trunk with woofer firing through the gap made by the center arm rest in the rear seats when it is down.

I would like to port the box to get the most out of it and have obtained some box size and port length documentation form Orion to use as a guide.

I was planning to port using a round port up through the hole in the parcel shelf above the rear seats where the rear speakers would be (removing the rear speakers of course)

If I were to design my box like this I have a few questions

1 - If I dual port the box, one port on each side to each of the rear speaker location is it as simple as halving the port length for two port ie. 1x port of 4" diameter and 8" length would port to the same frequency as 2x 4" diameter ports of 4" length?

2 - The section between the front of the enclosure where the subwoofer is located and the back of the rear seats isn't going to be sealed against the rest of the trunk before it reaches the hole between the rear seats. Is that something that would need to be taken into account? Or because air is able to escape around the outside of the box to the rest of the trunk will this have no effect? Also the size of the hole the arm rest being down creates will this need to be accounted for?

Yes I know I could apply the KISS principle and just use one port but I was wanting to keep things symmetrical.

[Joe X]

Answer to 1 = not at all, use this: http://www.psp-inc.com/tools.html to calculate the length of the ports, and also two 4" ports likely will not be enough port area for that 15" at that power. I would just keep it s-simple and do a ~ 65 square inches slot port driver's side.

[RooTxBeeR]

To the OP, I don't get why this guy above said keep it simple with a slot port. Do what you said and do some slot ports. Have them port all the way up, and maybe like a half inch through your rear deck, and as deep as you can go into your box until you reach the wanted port area. Aereo ports are WAYYYYYY simpler than a slot port, because you will most likely have to bend it if you go that route.

For your second question, you do not HAVE to seal off the box from the trunk. But if you are going to have the hole down, and port through the rear deck. I am pretty sure you would benefit greatly from sealing off the trunk, so the only place air is moving around is inside the cabin, and not the trunk also.

[timc31610]

!. No, they are not the same. For a 4.5ft3 box 1 4" port at 3.22" would tune you to 35hz. Two 4" ports at 9.36" ea would tune you to 35. Also you would have double the port area on two 4's. Port area for two 4" ports would be around 25" square. For that 15 you will likely want more port area to minimize port noise.

[Jeremy Coc]

Answer to 1 = not at all, use this: http://www.psp-inc.com/tools.html to calculate the length of the ports, and also two 4" ports likely will not be enough port area for that 15" at that power. I would just keep it s-simple and do a ~ 65 square inches slot port driver's side.

Thanks for the reply and the URL

I plugged some figures into that to see how they turned out

Volume of box in cuft - 4.5

Tuning frequency - 38hz

Port diameter - 4 (I assume this is inches)

Number of ports - 2

For that I get

Straight length port required - 7.497391812865496

Let's say 7.5

Flaried port length required - 8.497391812865496

Again let's say 8.5

If these are inches doesn't seem do difficult to get hold of 2x 90 bend of ploy pipe and position them high of the end of the box so the align with the speaker holes and attach straight piece to reach the height of the rear parcel shelf. I guess maybe 4 inches of length in the 90 degree bend and another 4" of straight to get the height

If I've got measurements wrong or I am over simplifying things please let me know

!. No, they are not the same. For a 4.5ft3 box 1 4" port at 3.22" would tune you to 35hz. Two 4" ports at 9.36" ea would tune you to 35. Also you would have double the port area on two 4's. Port area for two 4" ports would be around 25" square. For that 15 you will likely want more port area to minimize port noise.

Are you saying if you double the number of ports you have to triple the length of each port in order to get the same frequency. If so that doesn't seem to difficult and a very easy way to work it out however using that calculator provided by the other user it worked out doubling the number of ports made each port length slightly less than 3 times longer. So I'm guessing its just a guide or is there another factor involved.

Also what would you recommend for port diameter then as the hardware store has bigger pipes xD

[Joe X]

If I've got measurements wrong or I am over simplifying things please let me know

Problem here is that 2 4" aeros is pretty much low port area for that sub used at full capacity, that will lead to inefficiency and probably port noise specially if using non flared round ports, raw PVC pipe you plan to use, furthermore port noise is more noticeable when it occurs inside the cabin than inside the trunk, here's the hard part: if you increase the diameter of the pipes (or the number), the calculator will tell you they need to be longer and you will likely run into issues fitting them.

[Jeremy Coc]

What do you recommend as a good cross sectional port area for my setup then?

[Joe X]

Say 3 4" ports but flared and that would be nothing great really.

[timc31610]

Answer to 1 = not at all, use this: http://www.psp-inc.com/tools.html to calculate the length of the ports, and also two 4" ports likely will not be enough port area for that 15" at that power. I would just keep it s-simple and do a ~ 65 square inches slot port driver's side.

Thanks for the reply and the URL

I plugged some figures into that to see how they turned out

Volume of box in cuft - 4.5

Tuning frequency - 38hz

Port diameter - 4 (I assume this is inches)

Number of ports - 2

For that I get

Straight length port required - 7.497391812865496

Let's say 7.5

Flaried port length required - 8.497391812865496

Again let's say 8.5

If these are inches doesn't seem do difficult to get hold of 2x 90 bend of ploy pipe and position them high of the end of the box so the align with the speaker holes and attach straight piece to reach the height of the rear parcel shelf. I guess maybe 4 inches of length in the 90 degree bend and another 4" of straight to get the height

If I've got measurements wrong or I am over simplifying things please let me know

!. No, they are not the same. For a 4.5ft3 box 1 4" port at 3.22" would tune you to 35hz. Two 4" ports at 9.36" ea would tune you to 35. Also you would have double the port area on two 4's. Port area for two 4" ports would be around 25" square. For that 15 you will likely want more port area to minimize port noise.

Are you saying if you double the number of ports you have to triple the length of each port in order to get the same frequency. If so that doesn't seem to difficult and a very easy way to work it out however using that calculator provided by the other user it worked out doubling the number of ports made each port length slightly less than 3 times longer. So I'm guessing its just a guide or is there another factor involved.

Also what would you recommend for port diameter then as the hardware store has bigger pipes xD

Doubling the number of ports doubles the total port area which in turn causes you to have to increase port length to maintain your desired tuning. Have you downloaded torres yet?

[Krakin]

Torres isn't the best option for finding the tuning for multiple aero-ports. The calculator that does is already linked above.