Precision Port Quandry - Home Theater Forum and Systems - HomeTheaterShack.com

Old 02-18-09, 08:47 PM Thread Starter
Elite Shackster

Jacen

Join Date: Apr 2006
Location: Bay Area, California
Posts: 1,582
Precision Port Quandry

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
1. Calculate length of port needed
2. 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.
3. Trim center tube to 5" shorter than the calculated length.
4. 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?
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Old 02-18-09, 08:59 PM
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Kevin

Join Date: Feb 2008
Location: Nazareth, PA
Posts: 101
Re: Precision Port Quandry

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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Old 02-19-09, 09:14 AM
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Dave

Join Date: Feb 2009
Location: Orange County, CA
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Re: Precision Port Quandry

Quote:
JCD wrote: View Post
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.

Dave

Orange County, California
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Old 02-19-09, 09:20 AM
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Mike

Join Date: Apr 2007
Posts: 19,397
Re: Precision Port Quandry

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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Old 02-19-09, 09:30 AM
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Kevin

Join Date: Feb 2008
Location: Nazareth, PA
Posts: 101
Re: Precision Port Quandry

Quote:
Mike P. wrote: View Post
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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Old 02-19-09, 10:03 AM
Elite Shackster

Mike

Join Date: Apr 2007
Posts: 19,397
Re: Precision Port Quandry

Quote:
zero the hero wrote: View Post
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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Old 02-24-09, 05:45 PM Thread Starter
Elite Shackster

Jacen

Join Date: Apr 2006
Location: Bay Area, California
Posts: 1,582
Re: Precision Port Quandry

Quote:
DaveC wrote: View Post
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..
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