# Precision Port Quandry



## JCD (Apr 20, 2006)

A friend and I are building a new set of speakers from scratch. It's a ported MTM design. To maximize the performance we decided to go with the flared Precision Ports. 

Here's where the quandry pops up -- when I calculated the port length, it came up with 4.45".

The instructions for the port say


Calculate length of port needed 
Determine proper speaker & port placement before cutting any holes. The Precision Port should be placed at least one port diameter away from any inside walls, if possible. 
Trim center tube to 5" shorter than the calculated length. 
The Precision Port should be 1" longer than Lv when assembled.

Well, the problem is that 4.45-5 = -0.55. Unless we're getting into some metaphyscial discussions, we've got a problem.. what can we do? Just use regular 3" PVC pipe instead of the flared ports already purchased? Or will having a port an extra 0.55" longer matter? :mooooh::gah:


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## zero the hero (Feb 24, 2008)

well what size is the enclosure? What tune are you trying to accomplish? Whats the difference in tuning between your "optimum" size and 5"? 
In all likeliness the difference is miniscule and you won't notice. I'd use the flared.


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## DaveC (Feb 10, 2009)

JCD said:


> 4. The Precision Port should be 1" longer than Lv when assembled.


The last part here is a general purpose fudge factor. It should be pretty close for most circumstances though. Do the modeling, and see what difference a 1/2" difference in port length makes. My experience is that there are usually unaccounted for losses between the model and the actual article, and that a little longer port helps to make up for those anyway.
As zero said, I doubt there will be any significant difference between the two.


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## Mike P. (Apr 6, 2007)

Another option would be to use 2 inch flared ports as long as the air speed stays acceptable for your design.


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## zero the hero (Feb 24, 2008)

Mike P. said:


> Another option would be to use 2 inch flared ports as long as the air speed stays acceptable for your design.


But, a 2" port would have to be 1 1/2 inches long to equal the tuning of a 3" port 4 1/2 inches... that's called a hole 

How about a 4" flared port?


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## Mike P. (Apr 6, 2007)

zero the hero said:


> But, a 2" port would have to be 1 1/2 inches long to equal the tuning of a 3" port 4 1/2 inches... that's called a hole


You're right, I had it backwards.


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## JCD (Apr 20, 2006)

DaveC said:


> The last part here is a general purpose fudge factor. It should be pretty close for most circumstances though. Do the modeling, and see what difference a 1/2" difference in port length makes. My experience is that there are usually unaccounted for losses between the model and the actual article, and that a little longer port helps to make up for those anyway.
> As zero said, I doubt there will be any significant difference between the two.


Yeah, I was being a little too much of a ninny.. plugging the values into WinISD ended up with two curves that were pretty close to identical. I think there might have been a 1hz difference in where it started to roll off and where it ended..

Like I said, just being a ninny.. :doh:


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