2245 tuning

[Sandor the hun]

Hello, can some one help me tune a 12 cu foot box to 25 Hz with a 2245 and would like to make to port square, I used winisd the dimensions are tube.
The numbers are .102 width and .076 long.
Thank you

[svollmer]

It's simple geometry. A square port should have the same area as a circular one IF the length is the same. For example, if a round port that is 4 inches long has an area of 81 square inches, a square port would be 9 inches by 9 nine inches (81 square inches) and the same length (4 inches) as the circular one.

The area of a circle is Pi times the Radius squared, or A = 3.14 × r2

[Lee in Montreal]

The numbers are .102 width and .076 long.

Are you affirmative these are good measurements? :D

BTW Area of a cercle is Pi x radius^2

On a 2245, I suggest two 6" ports. Or one 8" port. Or the square equivalent.

BTW If you are into square ports and want to make a rigid cabinet, may I suggest something like this. It allows to brace the sides, which act as ports too.

http://www.audioheritage.org/vbulletin/showthread.php?36804-Any-Canadian-2245-woofer-for-sale&p=375848&viewfull=1#post375848

Lee

[gasfan]

Hello, can some one help me tune a 12 cu foot box to 25 Hz with a 2245 and would like to make to port square, I used winisd the dimensions are tube.
The numbers are .102 width and .076 long.
Thank you

Do a search for this '2245 Subwoofer Box 12 Cubic Ft.'

[Lee in Montreal]

Calculating port dimensions

http://psp-inc.com/tools2.html

8" port is 50.2sq.in (deduct your own square dimension).
Length is 13.2"

[Ruediger]

General Audio Discussion forum ->
Technical References thread ->
Thiele Paper post ->
attached Thiele Paper I of II ->
bottom of page 189 -> page 190

Ruediger

[rusty jefferson]

In his article about the 2245h sub cabinets, Greg Timbers shows a plan for a 12 cubic foot box with a 9" diameter round duct. He states "... for the 25hz, unassisted 4th order alignment, duct length should be 20"....." So, if one wants a 20" long duct with the same volume (appox 1275 cubic inches), but square, I think you would make an 8"x8"x20" duct (appox 1280 cubic inches) and have the same effect as a 9"x20" round duct. I am often wrong about such things, however. Please correct me if I am here.

http://www.lansingheritage.org/images/jbl/reference/technical/1983-subs/page6.jpg

[Sandor the hun]

Thank you all so much.

[dr_gallup]

In his article about the 2245h sub cabinets, Greg Timbers shows a plan for a 12 cubic foot box with a 9" diameter round duct. He states "... for the 25hz, unassisted 4th order alignment, duct length should be 20"....." So, if one wants a 20" long duct with the same volume (appox 1275 cubic inches), but square, I think you would make an 8"x8"x20" duct (appox 1280 cubic inches) and have the same effect as a 9"x20" round duct. I am often wrong about such things, however. Please correct me if I am here.

http://www.lansingheritage.org/images/jbl/reference/technical/1983-subs/page6.jpg

Your calcs are correct. That's the Audio Magazine article I used to to make my 2245 sub cabinet back in 83 or 84. There 5 more pages to that article, just change the page number in the link if you want to read them. I used a rectangular "slot" duct across the short side, it was easier given my limited woodworking skills. I've been happy with it although in my younger days I did tear up two drivers even with a subsonic high pass filter.

[svollmer]

In his article about the 2245h sub cabinets, Greg Timbers shows a plan for a 12 cubic foot box with a 9" diameter round duct. He states "... for the 25hz, unassisted 4th order alignment, duct length should be 20"....." So, if one wants a 20" long duct with the same volume (appox 1275 cubic inches), but square, I think you would make an 8"x8"x20" duct (appox 1280 cubic inches) and have the same effect as a 9"x20" round duct. I am often wrong about such things, however. Please correct me if I am here.

http://www.lansingheritage.org/images/jbl/reference/technical/1983-subs/page6.jpg

That's exactly what mine are. I used one side of the square port as a shelf brace to tie four of the panels together.

http://www.audioheritage.org/vbulletin/showthread.php?25778-2245H-Sub-Woofer-Project/page3