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View Full Version : How to calculate slot port length

shizzzon
05-04-2008, 02:05 PM
Ok, i've been trying to figure out what is happening here.

I found a calculator for doing this here -
http://www.carstereo.com/help/Articles.cfm?id=31

So, i got something that can give me the answer, but what i wanna is why does it give me this "other" answer as you will see below-

internal box dimensions-
16.25" high
16.25" deep
34.75" wide

First calculation will be side firing with port as tall as box.
tuning- 40hz
volume - 3.8cuft
size - 16.25" high x 3.75" wide
Length required - 18.69"

Second calculation(this is where it gets weird)
tuning- 40hz
volume - 3.8cuft
size - 3.75" high x 16.25" wide (i have now just made the port the whole depth of the box instead of the whole height of it. Port still uses 3 of 4 walls of the box just like it did before)
Length required - 12.44" ?!?!

Why is this method 6.25" shorter but the design is the same practically?

I know square ports and slot ports are way different as slot ports effect the physical length calculation so i do not understand what is going on here.

IgnoreMe
05-04-2008, 09:02 PM
Ok, i've been trying to figure out what is happening here.

I found a calculator for doing this here -
http://www.carstereo.com/help/Articles.cfm?id=31

So, i got something that can give me the answer, but what i wanna is why does it give me this "other" answer as you will see below-

internal box dimensions-
16.25" high
16.25" deep
34.75" wide

First calculation will be side firing with port as tall as box.
tuning- 40hz
volume - 3.8cuft
size - 16.25" high x 3.75" wide
Length required - 18.69"

Second calculation(this is where it gets weird)
tuning- 40hz
volume - 3.8cuft
size - 3.75" high x 16.25" wide (i have now just made the port the whole depth of the box instead of the whole height of it. Port still uses 3 of 4 walls of the box just like it did before)
Length required - 12.44" ?!?!

Why is this method 6.25" shorter but the design is the same practically?

I know square ports and slot ports are way different as slot ports effect the physical length calculation so i do not understand what is going on here.

its a problem with the program. however its coded by the designer, is the issue.

just use winisd which gives a port length of 20.45 for both designs.

my guess is that website tries to calculate port end correction and somewhere along the lines he screwed it up how it calculates it. just use winisd for port lengths. then subtract half your port width from it, to get physical port length (ie, what the sub needs to see in order for the tuning to be right on). i know some people said winisd calculated end correction, but it seems obvious it doesnt since the port length doesnt change even if the port area is the same.