Need some help with box design

[Joshdashef]

So I've thrown myself for a loop here and I'm stuck on how to achieve a lower tune for a dual 12 box.

Drivers: 2x P3D4 12s - Specifications

I'm using WinISD currently and I have inputted all the specifications I could from RF's website letting the program calculate the rest. 

My maximum dimensions possible are 36 Depth x 15 Height x 22.5 Width (Inches) so roughly 7 ft cubed. Yes tons of space but these specific drivers recommend around 1.8 cubed for a ported box. So with two of these I figure 1.8 x 2 plus woofer displacement of .106 cubed each. Leaves me with a required air space of 4 cubed for the woofers. 

 

What I'm stuck on is how do I figure out the best way to tune these to somewhere below 40, preferably 32-35. Would I be better off using a flared aero port, or a slotted port? 

Or am I trying to use the wrong drivers to achieve a lower freq response and should go for a band pass box 

 

[Triticum Agricolam]

You can tune the box to whatever you want, you just need to make the port longer.  When determining your port dimensions make sure the port is large enough to handle the amount of power you are going to be running. 

Both slot ports and aero ports work well as long as they are implemented properly. 

[Joshdashef]

Sorry its a day after my original post.

I was trying to figure out how to tune to 32hz and just wanted your input on if this would work. 

I went on SketchUp to make a basic design to go from and making cutting step easier.

For the purpose of this lets say I want to use 3/4 '' Birch Ply. (Not sure if I should double baffle or not)

This is my idea; simple two chamber meeting to a single port with double the width as the smaller ones. If I understand correctly to measure out port length I go from the middle of the outside port (next to the subs) and measure to the middle of the intersecting two smaller ports, and split to either side to finish the length off.

Outer Dimensions:  H: 15 1/2 ''   W: 37 1/2 ''    D: 15 1/2 ''

Inner Dimensions:   H: 14 ''   W: 36 ''    D: 14 ''

Max depth is around 20 "

My question is this website correct?

*looking at this specific 4x14 port and length I would be left with between 1-2 inches for airflow between the subs little chamber and the port "tube" would that be okay or should I allow greater airflow? so bump up the tuning to 33/34 hz.

 

Sidenote* How would I know I'm not overpowering the port and introducing noise? WinISD Air Velocity Chart? I've seen some posts say stay below 30 meters / sec but others vary.

 

 

Any help would be appreciated. I'm completely new to this, but I'm wanting to do it right the first time.

 

 

[ckeeler11]

the problem you have is on the calculator you enter the gross volume of the box. When you add a port the net volume goes way down to 2.88 cu.ft. and tuning goes up to 38 Hz. you need more space for 2 12's

[Joe X]

So here is a suggestion for your reference, power: to sub(s) rated, amp subsonic filter to 28Hz, minimum port clearance 4 1/2", figure is just an assembly guide:

NOTE: If building outside you need to build a cardboard dummy box to test fit in it's way inside.

 

 

 

[Joshdashef]

22 hours ago, Joe X said:

So here is a suggestion for your reference, power: to sub(s) rated, amp subsonic filter to 28Hz, minimum port clearance 4 1/2", figure is just an assembly guide:

NOTE: If building outside you need to build a cardboard dummy box to test fit in it's way inside.

 

 

 

Would the calculated volume (4^3ft) be after displacement or before? 

I'm assuming its net since the external dimensions - wood thickness give 5.98 Cubic feet volume.

 

Another question. Would the inclusion of the 45 to 45 point in the middle of the port be more efficient than without? 

 

Btw thank you for the reference image/post 

[Joshdashef]

On 10/31/2017 at 11:12 AM, ckeeler11 said:

the problem you have is on the calculator you enter the gross volume of the box. When you add a port the net volume goes way down to 2.88 cu.ft. and tuning goes up to 38 Hz. you need more space for 2 12's

Will keep that in mind. Thank you for your help!

[Mr DeeBeez]

The 45's in the port help direct the air out of the port. It helps air flow. I would definitely recommend doing that 

[Joe X]

13 hours ago, Joshdashef said:

Would the calculated volume (4^3ft) be after displacement or before? 

I'm assuming its net since the external dimensions - wood thickness give 5.98 Cubic feet volume.

 

Another question. Would the inclusion of the 45 to 45 point in the middle of the port be more efficient than without? 

 

Btw thank you for the reference image/post 

 

Yes the volume stated is net, the 45s are almost ornamental, except the ones inside the port which may reduce turbulence at the turn, bear in mind that if those are not done properly performance would be hurt sometimes severely, it's in many cases safer not to do them when you can't do them perfectly and the correct size.