rpfuror

02-06-2007, 09:46 AM

I have seen hundreds of question in regards to box design, I wanted to put out some basic fundamentals so that if you really want to design something yourself you will have a starting point, which is if you are willing to dig thru my logic.

First, I am not going to cover calculation of port length and width. I have described this a couple times on the forums (so you can search my nick) and there are plenty places to get the calculation you need (jl's site, carstereo.com many others).

I'll try to lead you in the right direction, as it can be a cumbersome process as there are many way to calculate the same thing, I will give you an idea on how I started to do it with basic math.

You determine port length by use of internal box height, desired tuning frequency and target Net volume. Now this volume is never going to be "fixed" as when you add of take away length you change the volume (if you basing this value on final external L x external W x external H of the enclosure).

I’m only going to speak to a “slot port design”.

Ok, here is the fun stuff; you have to work with internal volumes not external.

You will need the following to determine tuning and box dimensions.

eH = Target external Height of your box (needed also for port calculation)

eW = Target external Width of your box

eL = Target Box External Length

wT = Wood Thickness

Lv = Calculated port length (I’m not going to touch this here)

pW = Determined port width (I’m not going to touch this here)

Vb = Target net volume (needed also for port calculation) in cu/inches

Note: add your extra internal displacements in cu/inches to Vb

Calculate the internal height of the port/box; I will call that iH (internal Height).

iH = eH – (2 * wT)

This value gets plugged into the equations for tuning.

Calculate the internal width of the box; I will call this iW (internal Width).

iW = eW – (2 * wT)

Now you can keep changing numbers until you get somewhere around the values you are looking for or you can stick with 2 dimensions, to make things easy use height as one variable as to not change the length of the port, to solve for the other. In this example I will be solving for Depth based on Length and Height

You will have to add the thickness of one wall into this equation; I will call this ipW (internal port W).

ipW = pW + wT

Next determine total internal volume displaced by the port, I will call that pV (port Volume).

pV= Lv x iH x ipW

Now you need to add the internal port volume to the net volume you are targeting, I will call this giV (gross internal Volume).

giV = pV + Vb

Now you have all you need calculate your correct external Depth of your box to fit your target port and net volumes, I will call this iD (internal Depth).

iD = giV / (iH * iW)

Finally calculate the external depth; I will call this eD (external Depth).

eD = iD + (2 * wT)

You have just designed your box eW x eH x eD !!!

First, I am not going to cover calculation of port length and width. I have described this a couple times on the forums (so you can search my nick) and there are plenty places to get the calculation you need (jl's site, carstereo.com many others).

I'll try to lead you in the right direction, as it can be a cumbersome process as there are many way to calculate the same thing, I will give you an idea on how I started to do it with basic math.

You determine port length by use of internal box height, desired tuning frequency and target Net volume. Now this volume is never going to be "fixed" as when you add of take away length you change the volume (if you basing this value on final external L x external W x external H of the enclosure).

I’m only going to speak to a “slot port design”.

Ok, here is the fun stuff; you have to work with internal volumes not external.

You will need the following to determine tuning and box dimensions.

eH = Target external Height of your box (needed also for port calculation)

eW = Target external Width of your box

eL = Target Box External Length

wT = Wood Thickness

Lv = Calculated port length (I’m not going to touch this here)

pW = Determined port width (I’m not going to touch this here)

Vb = Target net volume (needed also for port calculation) in cu/inches

Note: add your extra internal displacements in cu/inches to Vb

Calculate the internal height of the port/box; I will call that iH (internal Height).

iH = eH – (2 * wT)

This value gets plugged into the equations for tuning.

Calculate the internal width of the box; I will call this iW (internal Width).

iW = eW – (2 * wT)

Now you can keep changing numbers until you get somewhere around the values you are looking for or you can stick with 2 dimensions, to make things easy use height as one variable as to not change the length of the port, to solve for the other. In this example I will be solving for Depth based on Length and Height

You will have to add the thickness of one wall into this equation; I will call this ipW (internal port W).

ipW = pW + wT

Next determine total internal volume displaced by the port, I will call that pV (port Volume).

pV= Lv x iH x ipW

Now you need to add the internal port volume to the net volume you are targeting, I will call this giV (gross internal Volume).

giV = pV + Vb

Now you have all you need calculate your correct external Depth of your box to fit your target port and net volumes, I will call this iD (internal Depth).

iD = giV / (iH * iW)

Finally calculate the external depth; I will call this eD (external Depth).

eD = iD + (2 * wT)

You have just designed your box eW x eH x eD !!!