Converting round port to slot port?

S7910

I'm trying to convert a 3" x 3.65" round port to a slot port, and need a refresher on how this works. I know that the area of the port needs to be maintained, but don't remember if it's the height (diameter) or length that also stays the same. I've done some searching already, but the explanations I've found (to me anyways) aren't very clear or just gloss over the topic.

TIA

ThumperTom

I always use winISD to convert.  Adjust the tuning to match your 3" X 3.65" then select square port and enter your target height and width to get the length.  Online calculator can do the same thing. http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201.htm

Wolf

Pi * R^2 = L * W

jholtz

How about a spreadsheet from our friend Paul Carmody?

HTH

Jim

Gowa

BassBox Pro has that.

PWRRYD

As Wolf posted:   Pi x r^2 = L x W  so:

3.1415 × (1.5")^2 = 7.068 in^2  (~ 7 sq in)

If your slot port width is 7", then the slot port height would be 

 7 sq in / 7" = 1"   (7" wide x 1" high)

            Or

7 sq in / 3.5" = 2"   (3.5" wide x 2" high)

Etc

ani_101

the area of the slot port should be the same as the area of the round port. Keep the length same.

If you want to really optimize, usual the round ports are in the center away from the walls, whereas slot ports use the walls as one of the side - this does affect the lenght of the port for a particular tuning - Jeff B has a formula for calculating how much of the lenght should be altered if you are near a wall rather than away from a wall (at least twice the diameter of the port... Or just skip it, you will be in the ball park

jhollander

The other rule of thumb was to keep the height to width ratio no more than 1 to 7, (1 to 9?)   

I can't remember the exact end correction/ boundary factor for the slot port, but I've used port length -1 port height multiple times and been very close to the box model.

S7910

Thanks for the answers, all. They've helped clear up the concept.

Wolf

Pretty sure that is 1 to 8 ratio. Rory relayed that info.

Ed_Perkins

Here's a picture that shows how the K value changes with slot port location.  It was taken from this PETT thread: http://techtalk.parts-express.com/forum/tech-talk-forum/66368-q-slot-port-length.

ReelFan

How are these calculations or examples affected when a speaker has those old fashioned slot vents sometimes found on early speakers?  I'm referencing my old EV speakers that have roughly (4) 1/4" wide by 10" vents, 3/4" deep on the back of the cabinet.  Was there a specific purpose for those vents, as opposed to a single vent of round or rectangular shape?  Can the above vents shown by Ed Perkins be used if you desired to seal up the back of such a  speaker?