12W3v2 ported enclosure question

[memphiskane]

I am trying to wrap my head around enclosure tuning but for some reason it is just not making sense to me. So I am hoping someone can simplify it for me. The JL manual recommends a ported box that is 1.75 net volume tuned at 30.3. I spoke with tech support to see if they had the port dimensions using a tube vs slot and was told to use a 4x15 tube.

Here is where I get confused. The box itself will need to be 1.82 to account for woofer displacement. Does the port itself need to be accounted for. If so do you account for just the port material or do you have to account for the port material plus internal volume of the port and add that to the total box volume?

[minbari]

Originally Posted by memphiskane

I am trying to wrap my head around enclosure tuning but for some reason it is just not making sense to me. So I am hoping someone can simplify it for me. The JL manual recommends a ported box that is 1.75 net volume tuned at 30.3. I spoke with tech support to see if they had the port dimensions using a tube vs slot and was told to use a 4x15 tube.

Here is where I get confused. The box itself will need to be 1.82 to account for woofer displacement. Does the port itself need to be accounted for. If so do you account for just the port material or do you have to account for the port material plus internal volume of the port and add that to the total box volume?

yes. if the box is supposed to be 1.75 cuft net, then you have to make the box big enough to compensate for woofer and port displacement. you can not consider ANY part of the port in internal volume. if you have a 4 x 15" port, then you have to subtract .11cuft (pi x R^2 x length)


****edit 4 x 15 port with 1.75 cuft box would be 33hz. if you want 30hz tune, you need a 4 x 18.5" port

[memphiskane]

Ok, that makes sense was what I thought but just had to confirm. Now one last question on this.

So the wall thickness of the box is 3/4 and when you remove that thickness to add the port you gain that area in box volume. Should that 3/4 be removed when calculating the port volume to be added to the endclosure? Hope my question makes sense.

[minbari]

you would subtract the 3/4" from the length. you only want the volume of the port that is actually in the volume of the box. if you recalculate it, I think you will see this is almost a non-issue

4" x 18.5" port = .135 cuft

if you compensate for the 3/4" wood = .129 cuft

[memphiskane]

Ok, thought I was done but I guess not. The more answers I get the more questions I have.

The front baffle of my box is not big enough to do the 4 in port on the front. If I place it on the side what would be better or would it not make a difference. Towards side wall, towards open cabin?

If I wanted to do it on the front could I split the 4 in port into 2/2 in ports the same length or would that somehow change the calculations?

[minbari]

Originally Posted by memphiskane

Ok, thought I was done but I guess not. The more answers I get the more questions I have.

The front baffle of my box is not big enough to do the 4 in port on the front. If I place it on the side what would be better or would it not make a difference. Towards side wall, towards open cabin?

as long as you have at least the diameter of the port in clearance from the mouth of the port, you will be fine. this is for the exterior mouth and the interior one. in this case 4" of clearance. if I had to pick, I would vent it into the cabin.

If I wanted to do it on the front could I split the 4 in port into 2/2 in ports the same length or would that somehow change the calculations?

(2)2" ports would be a bad idea. you would have to recalculate the length, but that is trivial. it would have 1/2 the port area and port velocity would go through the roof. 4" port is already on the line for that sub. wouldn't do it.

if you have to, you can bend the port too. get a 4" 90° elbow and turn the port inside the box.