Need some help regarding these ports

Xristo · 5th November 2004, 05:31 AM

hey guys, currently im build pair of bookshelf speakers using the vifa p17 woofer and vifa d25ag tweeter. I am using John Krutke's design off his website. The design uses a 38mm diameter port by 74 mm long, however i cant seem to find 38 mm dia ports. the only ports i can find are 35mm internal diameter at the opening but they taper off to 29 mm at the end, is there a way i can use these ports and still get the same tuning frequency as used in the original design? thanks

Nasse · 5th November 2004, 07:09 AM

I only have limited experience on these but used WinISD software that was online somewhere and I believe the result was quite near what was simulated

But these tools are for ordinary ducts that have same area at full length and at beginning and end. I believe you can make rectangular duct, calculate the area and give the program a diameter that gives same area.

For one project I cut three tubes at slightly different lenght and took the one that sounded "best". Not very scientific method I quess

This was not an answer for your custom pipes, but maybe you can use the software and use some other dimension tube that is available for you

Ron E · 5th November 2004, 09:24 PM

They don't have 1.5" PVC down under?

5th November 2004, 05:31 AM	#1
Xristo diyAudio Member Join Date: Jun 2004 Location: Melbourne	Need some help regarding these ports hey guys, currently im build pair of bookshelf speakers using the vifa p17 woofer and vifa d25ag tweeter. I am using John Krutke's design off his website. The design uses a 38mm diameter port by 74 mm long, however i cant seem to find 38 mm dia ports. the only ports i can find are 35mm internal diameter at the opening but they taper off to 29 mm at the end, is there a way i can use these ports and still get the same tuning frequency as used in the original design? thanks

5th November 2004, 09:24 PM	#3
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	They don't have 1.5" PVC down under? __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

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5th November 2004, 07:09 AM	#2
Nasse diyAudio Member Join Date: May 2004 Location: Scandinavia	I only have limited experience on these but used WinISD software that was online somewhere and I believe the result was quite near what was simulated But these tools are for ordinary ducts that have same area at full length and at beginning and end. I believe you can make rectangular duct, calculate the area and give the program a diameter that gives same area. For one project I cut three tubes at slightly different lenght and took the one that sounded "best". Not very scientific method I quess This was not an answer for your custom pipes, but maybe you can use the software and use some other dimension tube that is available for you

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