Have i got these calculations right?

[motion 0]

Hey guys,

Will be building my first box in the next week or so and I really just want to make it right the first time so i would be really grateful if you could check over my numbers before i go any further.

Specs

2003 Ford focus

12" SI Mag re coned with fi softparts. So basically its the same spec as a Fi Q

Aim 32 hz @ 2.5cuft (biggest recommended box for this sub)

Subwoofer displacement - 0.16 cuft

Port Displacement - 0.69cuft (Really didn't know how to work this out! Do you calculate the port as a separate component or just account for the wood that makes the port if so this is wrong)

Baffles displacement - 0.10cuft (in my design i have quite a few baffles to brace the port along with the double baffled front and corners)

All the above added to the first figure makes a overall box size of 3.45cuft

Ok so onto the box dimentions

Width - 37.8 inch - 960mm

Height - 15.7 inch - 400mm

Depth - 14.16 inch - 373mm

Thickness - 1 inch - 25mm

Port Specs

Width - 3 inch - 76mm

Height - 13.7 inch - 348mm

Legnth - 25.44 inch - 646mm

How do they sound? I think everything is ok up until the port displacement which I am really not to sure if i have got right. Obviously i want the best sounding enclosure for this driver so i'm most defiantly open to advice from anyone. I should also mention i'm planning to kerf the MDF on the port to make it rounded, will this affect the port specs at all?

Thanks for the help guys its much appreciated!

Also have these if their any use to anyone

Gain

Phase

SPL

Edited October 16, 2011 by Motion

[motion 0]

no one out there that can help?

[S.DeYoung 968]

What exactly are you asking?

[ssh 924]

Port displacement is the total space that is used for the port along with the wood.

For example: port width: 4", port height: 6", port length: 8", 4x6x8= 192in^2 + the actual displacement of the wood used for the port.

[motion 0]

What exactly are you asking?

For someone to check over my calculations, as in the sub recommends it should be in a 2.5cuft enclosure. I'm guessing this is just the enclosure and doesn't take into account for any baffles, sub and port displacement? So in that case the above should be correct? Sorry i'm probably being really stupid but this is my first box and want it to sound right.

Port displacement is the total space that is used for the port along with the wood.

For example: port width: 4", port height: 6", port length: 8", 4x6x8= 192in^2 + the actual displacement of the wood used for the port.

So in this case my port will be 3 x 13.7 x 26.3 = 0.62554 cuft. Am i right in thinking i add this to the initial 2.5cuft? Along with the sub and baffle displacements.

Thanks

[ssh 924]

What exactly are you asking?

For someone to check over my calculations, as in the sub recommends it should be in a 2.5cuft enclosure. I'm guessing this is just the enclosure and doesn't take into account for any baffles, sub and port displacement? So in that case the above should be correct? Sorry i'm probably being really stupid but this is my first box and want it to sound right.

Port displacement is the total space that is used for the port along with the wood.

For example: port width: 4", port height: 6", port length: 8", 4x6x8= 192in^2 + the actual displacement of the wood used for the port.

So in this case my port will be 3 x 13.7 x 26.3 = 0.62554 cuft. Am i right in thinking i add this to the initial 2.5cuft? Along with the sub and baffle displacements.

Thanks

Lets say you have a box made out of 3/4" mdf with a double baffle where the speaker mounts, dimensions 10"x10"x10" and the port happens to be 4"x2"x7".

Subtract material thickness of 0.75 from 10", now you have 9.25", then there is the double baffle (0.75"+0.75"=1.5"), so 9.25"x9.25"x8.5" = 727.28" divide by 1728 to get cubic feet, 0.42ft^3

Then subtract port displacement. Lets say the port uses one of the outer walls so there's only one additional panel added. 4" height, 2" width, 7" depth. Only width needs additional accounting since it uses a 0.75" mdf panel. So 4x2.75x7 = 77 / 1728 = 0.044ft^3

0.42ft^3 - 0.044ft^3 = 0.376ft^3 net volume in this case.

Hopefully my math was correct, I'm not 100% sober and it's 9am... At least you get the jist of things. Hope I helped.

[///M5 2,833]

As others stated you didn't really get help as no one is really understanding what you want. From the title alone we understand you want calculation help, but outside that you've lost me. If its just to calculate 2.5cuft then that's do-able, but I hope not.

I am rather curious on your whole premise though. You included a picture of a frequency response plot for what you describe as:

2003 Ford focus

12" SI Mag re coned with fi softparts. So basically its the same spec as a Fi Q

Personally in your plots I don't at all see how you accounted for the cabin gain of the Focus and at the same time am also dying to know how you plotted a driver for which you have no T/S parameters. Unless of course you've measured them or had them measured, but you obviously aren't using manufacturers specs for a 12" SI Mag with some Fi Q parts....