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Flipx99
12-22-2005, 05:48 PM
How do I determine tuninging frequency at a given port volume. I looked at a manual that says a sub needs 2.25 cf + 3" x 11.25" x 18" long. Because my box is 14 inches tall, I would need 3 * 12.5 * 16.2 volume of port for them to be equal. With this volume, how can I determine reccomended port frequency. The manual only gives dimensions, not frequency.

saywhat?
12-22-2005, 06:03 PM
depending on the subs, im pretty sure its between 35 and 40. if its kicker, id say 37. without doing the math i wouldnt know exactly, but that looks to be right around there.

squeak9798
12-22-2005, 11:57 PM
How do I determine tuninging frequency at a given port volume. I looked at a manual that says a sub needs 2.25 cf + 3" x 11.25" x 18" long. Because my box is 14 inches tall, I would need 3 * 12.5 * 16.2 volume of port for them to be equal. With this volume, how can I determine reccomended port frequency. The manual only gives dimensions, not frequency.


Port length won't change as long as you keep the cross-sectional area the same.

3 * 11.25 = 33.75

33.75/12.5 = 2.7"

12.5 * 2.7" = 33.75

Make your port 2.7" wide rather than 3" wide and you can keep port length the same.

This ofcourse assumes that you will also have a net 2.25cuft enclosure volume.


Anyways, onward to your tuning frequency question........

Plug and chug, brother:

http://mobile.jlaudio.com/graphics/Support/Tutorials/Ports/Fb.jpg

Where Av is the cross-sectional area of the port (in square inches),
Lv is the length of the port (in inches) and
Vb is the enlcosure's net volume (in cubic inches).
Fb (what you are solving for) is the tuning frequency

Pop da Hatch
12-23-2005, 06:23 AM
BUMP I needed that formula - thanks bro

Flipx99
12-23-2005, 09:35 AM
Does net volume include or not include the port?

squeak9798
12-23-2005, 10:15 AM
NET enclosure volume is the volume of the enclosure after all displacement; i.e. port and sub displacement. So, after you subtract out the port displacement and sub displacement from your gross box volume, you are left with net volume.

Flipx99
12-23-2005, 10:21 AM
port displacement = port area x length?

squeak9798
12-23-2005, 10:24 AM
And you must include the thickness of the material used to build the port.

Flipx99
12-23-2005, 10:31 AM
but only on one side though, if it is a slotted port?

squeak9798
12-23-2005, 11:28 AM
Yes.

DBfan187
12-23-2005, 11:33 AM
port displacement = port area x length?

Port Displacement

if it uses of the sides of the box for one side of its port wall, then:
(port height) x (port length-wood thickness) x (port width + wood thickness) / 1728

if the ports in the middle of the box, and has its own walls, then:
(port height) x (port length - wood thickness) x [port width + 2(wood thickness)] / 1728

Flipx99
12-23-2005, 11:35 AM
Thanks very much!

Pop da Hatch
12-23-2005, 07:52 PM
good thread!