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mrknox 
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Posted: April 18, 2008 at 12:21 AM / IP Logged  
Does this program automatically take out speaker displacement, or do we have to figure that out?
And since were on the topic, why is it different when i figure out port legnths on this site than when I figure them out on WinISD?
Thanks in advance!
sedate 
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Posted: April 18, 2008 at 12:33 AM / IP Logged  

mrknox wrote:
Does this program automatically take out speaker displacement, or do we have to figure that out?

The volume you enter is the net internal volume - so no, port displacement, woofer displacement, MDF displacement is not accounted for.

Regardless - woofer displacement would have a negligble sonic impact.

mrknox wrote:
why is it different when i figure out port legnths on this site than when I figure them out on WinISD?

Ur entering a parameter incorrectly...?

What sort of box are you trying to design?  What parameters are you using?  What woofer do you want to use?  Maybe we could be more help...

"I'm finished!" - Daniel Plainview
aznboi3644 
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Posted: April 18, 2008 at 2:02 AM / IP Logged  
port lengths should not differ dramatically
stevdart 
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Joined: January 24, 2004
Location: Pennsylvania, United States
Posted: April 18, 2008 at 5:13 PM / IP Logged  

From WinISD Pro 0.50a7 Help file, under FAQ:

Q. Does WinISD add brace/driver/port displacements to calculated box volume?

A. From Janne Ahonen ( janne@lineateam.org)
--------------------------------------------------------------------------------

No. WinISD doesn't do guessing, and therefore shows net volume for your box. It would be hard to predict, how you are going to mount your driver. Or the port. Or how much and which kind of bracing you are going to use inside your box. For example, you could mount port completely external to the box, which case "usual" guess would be completely wrong. Bottom line is, that you must calculate and add any displacements by yourself to calculated box volume.

There can be and usually are slight differences in port length equations between the various programs' calculations.  If all is equal in your input from program to program, the differences are so minor that they are in fact neglible (in regard to real-life performance).

In other words, what everybody else said.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
mrknox 
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Joined: February 22, 2005
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Posted: April 18, 2008 at 10:26 PM / IP Logged  
I am building a vented enclosure for two 10 inch Cerwin Vega V-Max no divider.
I was using same internal volume, same port size, and was getting up to .5 inch difference on length of the port. I don't know if that would change things enough to notice (in real-life applications).
But let say I want to build a 6th order box, then even a 1/16 of an inch can change things drastically! So if two different programs differ even a little bit, how do I know whats right?
Thank you for the displacement issue, I looked long and hard and couldn't find it.
stevdart 
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Posted: April 18, 2008 at 11:05 PM / IP Logged  

If you are ever designing a box where the difference is noted as "drastic" within less of an inch (1/16th??), you should begin redesigning with a larger port so that the length in fractions of an inch becomes less critical.

A redesign may include changing the actual driver or box type as well as changing the size or shape of the port structure.

If you want a definitive answer to "who is right?", study the fundamental equations used in determining port length  http://www.diysubwoofers.org/misc/portcal.htm  and apply them to your project.

Note:  unless you have used the necessary tools to measure parameters of those Mister Vegas yourself, you are in for some experimentation in designing a vented box, no matter what box type you desire.  In fact, even if you had the woofers measured individually by a lab who specializes in such work, you will still have to allow for experimentation of port design to get the most desirable result.  Cabin (or room) nulls or nodes, cabin / room transfer function, and source material input are some of the factors that will influence the end result. 

Allow for adaptation of port length in your design, at the very least.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

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