Subwoofer, making the correct port length? using 2 of the walls

Toast_Master · 10th June 2011, 02:01 AM

Hey People

I just finished making the outside of the box some glued and some screwed so i can still do inside work, and ive made the mounting holes, just need to add bracing and the port ...

My question, Ive used winisd and Ive used it multiple times with subwoofers. It wants me to have a port length of 82 cms, which is fine just wondering how much shorter i can make it to be effectively make it 82cm? cause the port uses the bottom and left side of the enclosure meanings its in the bottom left corner

Ive read that when using 1 side that you subtract the height of the port to the length of the port.

Also some more information. it runs across the bottom and up the back wall and depending on how long its actually got to be maybe along the top in the same plane.

The internal dimensions are 35cm x 35xm x 55cmx

Thanks

Toast_Master · 10th June 2011, 11:05 AM

Bump lol, I want to make the port tomorrow

GM · 10th June 2011, 04:53 PM

Previously posted by 'bjorno' IIRC:

GM

Toast_Master · 10th June 2011, 10:28 PM

haha I found that while browsing the internet last night in bed on my ipod

Thanks

Toast_Master · 10th June 2011, 10:44 PM

entering the value there 1.728 makes the port longer cause when i entered it it makes the port go from 82 to 89 or am i meant to meant to play with it so it becomes 82 when i enter that correction value...also ive noticed that as soon as i type anything in there it adds length, the same length

vacuphile · 10th June 2011, 11:31 PM

There is no bloody way to calculate the length of a port correctly just based on theory.

Only in an itterative process of calculation and measurement you will know for sure what the tuning is. If you don't have measuring equipment, use the pea method. Lay the prototype on its back and put a dried pea, or some grains of rice, on the woofer. Do a sweep, and the frequency where the pea (or grains of rice) move least, that is where your Fm is.

bjorno · 11th June 2011, 02:07 AM

Quote:

Originally Posted by GM

Previously posted by 'bjorno' IIRC:

GM

Hi,

Thank you for posting the picture containing an incorrect formula!

I take the opportunity to update again

Another revision:

b

10th June 2011, 02:01 AM	#1
Toast_Master diyAudio Member Join Date: Apr 2006 Location: Tasmania, Launceston	Subwoofer, making the correct port length? using 2 of the walls Hey People I just finished making the outside of the box some glued and some screwed so i can still do inside work, and ive made the mounting holes, just need to add bracing and the port ... My question, Ive used winisd and Ive used it multiple times with subwoofers. It wants me to have a port length of 82 cms, which is fine just wondering how much shorter i can make it to be effectively make it 82cm? cause the port uses the bottom and left side of the enclosure meanings its in the bottom left corner Ive read that when using 1 side that you subtract the height of the port to the length of the port. Also some more information. it runs across the bottom and up the back wall and depending on how long its actually got to be maybe along the top in the same plane. The internal dimensions are 35cm x 35xm x 55cmx Thanks

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10th June 2011, 11:05 AM	#2
Toast_Master diyAudio Member Join Date: Apr 2006 Location: Tasmania, Launceston	Bump lol, I want to make the port tomorrow

10th June 2011, 10:28 PM	#4
Toast_Master diyAudio Member Join Date: Apr 2006 Location: Tasmania, Launceston	haha I found that while browsing the internet last night in bed on my ipod Thanks

10th June 2011, 10:44 PM	#5
Toast_Master diyAudio Member Join Date: Apr 2006 Location: Tasmania, Launceston	entering the value there 1.728 makes the port longer cause when i entered it it makes the port go from 82 to 89 or am i meant to meant to play with it so it becomes 82 when i enter that correction value...also ive noticed that as soon as i type anything in there it adds length, the same length

10th June 2011, 11:31 PM	#6
vacuphile diyAudio Member Join Date: Apr 2011 Location: Seaside	There is no bloody way to calculate the length of a port correctly just based on theory. Only in an itterative process of calculation and measurement you will know for sure what the tuning is. If you don't have measuring equipment, use the pea method. Lay the prototype on its back and put a dried pea, or some grains of rice, on the woofer. Do a sweep, and the frequency where the pea (or grains of rice) move least, that is where your Fm is.

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