Change port shape... port volume?

[lamski]

If I want to change the shape of a port from round to rectangular can I just use the same volume in any rectangular shape or is it more complicated then that?

I want to convert a round port of 1.375 diameter and 4.5 inches long to a rectangular slot port with a width of 5.5". The height and depth can be adjusted accordingly. What can I do?

[Wolf]

'End-area' or cross-sectional area should remain the same to use the same port. It's not a matter of volume. For a slot ROT, try not to exceed an 8:1 ratio of width to height of slot.

Later,
Wolf

[fastbike1]

I'll have to differ. If volume didn't matter, we'd never calculate with port length.

[LoveDoctor]

http://www.carstereo.com/help/Articles.cfm?id=31

I've always used this to calculate my ports. You can run some variations through here to get a match of tuning, but it seems odd that you want to take a round port with a surface area of 1.5"^2 and turn it into a slot port 5+ inches wide. Assuming you use at least 1" height for the slot, that's around 4 times the original surface area. The port will then need to be considerably longer than the original 4.5" length, with much greater total volume within the enclosure.

It might help to know what you are trying to do with your project, and the community here might have some more specific suggestions.

[lamski]

http://www.carstereo.com/help/Articles.cfm?id=31

I've always used this to calculate my ports. You can run some variations through here to get a match of tuning, but it seems odd that you want to take a round port with a surface area of 1.5"^2 and turn it into a slot port 5+ inches wide. Assuming you use at least 1" height for the slot, that's around 4 times the original surface area. The port will then need to be considerably longer than the original 4.5" length, with much greater total volume within the enclosure.

It might help to know what you are trying to do with your project, and the community here might have some more specific suggestions.

Its for a small nearfield desktop speaker that will be up against the wall. Im building the Microbe. Rear porting is not an option and a round front port would make the speaker too tall. Suggestions? Bottom port?

[mattp]

Which driver/enclosure volume do you currently have?

[Ludo]

If I want to change the shape of a port from round to rectangular can I just use the same volume in any rectangular shape or is it more complicated then that?

I want to convert a round port of 1.375 diameter and 4.5 inches long to a rectangular slot port with a width of 5.5". The height and depth can be adjusted accordingly. What can I do?

A 0.5" x 3" slot port would have the same cross section and approximately the same length as your 1.375" diameter port. I'd increase the length of the slot port by 0.25" to account for the inner opening being against one of the side walls.

[LSV8]

A 0.5" x 3" slot port would have the same cross section and approximately the same length as your 1.375" diameter port. I'd increase the length of the slot port by 0.25" to account for the inner opening being against one of the side walls.

What do you mean by "one of the side walls"? Not disagreeing with you, just do not understand what you mean! :) I would personally put that port in the center, using the bottom enclosure panel as the bottom of the port. Are you maybe suggesting that it be placed off to one side or the other using a side wall as the side of the port? Or did you simply mean the bottom of the cabinet when you said "side wall"?


Otherwise...

There isn't room for a front facing round port?

Maybe I'm looking at different plans than you are ( http://www.rjbaudio.com/Microbe/microbe.html ) but, there is 1.77" between the bottom of the woofer O.D. and the top of the bottom 3/4" board. Total of 2.7" from the bottom of the woofer O.D. to the base of the enclosure.

How is 1.77" not enough room for a 1.375" I.D port? You don't HAVE to use a port tube with a HUGE flange. Simple 1-1/4" schedule 40 PVC has a 1.380" I.D. with a 1.660" (slightly larger than 1-5/8") O.D.

[Chris Roemer]

What do you mean by "one of the side walls"? Not disagreeing with you, just do not understand what you mean! :) I would personally put that port in the center, using the bottom enclosure panel as the bottom of the port. Are you maybe suggesting that it be placed off to one side or the other using a side wall as the side of the port? Or did you simply mean the bottom of the cabinet when you said "side wall"?


Otherwise...

There isn't room for a front facing round port?

Maybe I'm looking at different plans than you are ( http://www.rjbaudio.com/Microbe/microbe.html ) but, there is 1.77" between the bottom of the woofer O.D. and the top of the bottom 3/4" board. Total of 2.7" from the bottom of the woofer O.D. to the base of the enclosure.

How is 1.77" not enough room for a 1.375" I.D port? You don't HAVE to use a port tube with a HUGE flange. Simple 1-1/4" schedule 40 PVC has a 1.380" I.D. with a 1.660" (slightly larger than 1-5/8") O.D.


ideas

http://techtalk.parts-express.com/album.php?albumid=38&pictureid=781

[Ludo]

What do you mean by "one of the side walls"? Not disagreeing with you, just do not understand what you mean! :) I would personally put that port in the center, using the bottom enclosure panel as the bottom of the port. Are you maybe suggesting that it be placed off to one side or the other using a side wall as the side of the port? Or did you simply mean the bottom of the cabinet when you said "side wall"?


Otherwise...

There isn't room for a front facing round port?

Maybe I'm looking at different plans than you are ( http://www.rjbaudio.com/Microbe/microbe.html ) but, there is 1.77" between the bottom of the woofer O.D. and the top of the bottom 3/4" board. Total of 2.7" from the bottom of the woofer O.D. to the base of the enclosure.

How is 1.77" not enough room for a 1.375" I.D port? You don't HAVE to use a port tube with a HUGE flange. Simple 1-1/4" schedule 40 PVC has a 1.380" I.D. with a 1.660" (slightly larger than 1-5/8") O.D.

Sorry for the confusion; I meant "side" in general tems for any panel including the bottom of the enclosure as you pointed out. Yeah, face the port opening towards the front and use the bottom of the enclosure as one side of the port.

[lamski]

What do you mean by "one of the side walls"? Not disagreeing with you, just do not understand what you mean! :) I would personally put that port in the center, using the bottom enclosure panel as the bottom of the port. Are you maybe suggesting that it be placed off to one side or the other using a side wall as the side of the port? Or did you simply mean the bottom of the cabinet when you said "side wall"?


Otherwise...

There isn't room for a front facing round port?

Maybe I'm looking at different plans than you are ( http://www.rjbaudio.com/Microbe/microbe.html ) but, there is 1.77" between the bottom of the woofer O.D. and the top of the bottom 3/4" board. Total of 2.7" from the bottom of the woofer O.D. to the base of the enclosure.

How is 1.77" not enough room for a 1.375" I.D port? You don't HAVE to use a port tube with a HUGE flange. Simple 1-1/4" schedule 40 PVC has a 1.380" I.D. with a 1.660" (slightly larger than 1-5/8") O.D.

Im actually going to be making the alternate version using the RS28AS Tweeter outlined in the same link. The one Dave J. Zachary made with Roman's help on the X-over. He had to move the woofer down the baffle due to the larger flange on the tweeter. If there is some way to make a slot port work I would like to try it otherwise I think I will have to use the regular port on the bottom.

Even with the 1.66 OD PVC pipe, thats cutting it pretty close and leaves me very little to no room for error.

[LSV8]

Im actually going to be making the alternate version using the RS28AS Tweeter outlined in the same link. The one Dave J. Zachary made with Roman's help on the X-over. He had to move the woofer down the baffle due to the larger flange on the tweeter. If there is some way to make a slot port work I would like to try it otherwise I think I will have to use the regular port on the bottom.

Even with the 1.66 OD PVC pipe, thats cutting it pretty close and leaves me very little to no room for error.

Gotcha! I didn't realize you were doing a dif design. In that case, Ludo's suggestion should work perfect.

[LSV8]

Sorry for the confusion; I meant "side" in general tems for any panel including the bottom of the enclosure as you pointed out. Yeah, face the port opening towards the front and use the bottom of the enclosure as one side of the port.

I figured that is what you meant... guess I just tried thinking too hard! lol

[Ludo]

I figured that is what you meant... guess I just tried thinking too hard! lol

We're in sync. :)

I would, however, like to correct the statement I made above from "I'd increase the length of the slot port by 0.25" " to decrease.

[lamski]

A 0.5" x 3" slot port would have the same cross section and approximately the same length as your 1.375" diameter port. I'd increase the length of the slot port by 0.25" to account for the inner opening being against one of the side walls.

So what would be the easiest way to make this port?

Is there anyplace that sells plastic rectangle extrusions or plastic non-round ports? Or would it be possible to use an alluminum tube?

I could use something like this type of a port if I can find it:

http://www.sweetwater.com/images/closeup/xl/1600-LSR2325P_back.jpg

[Jeff B.]

I'll have to differ. If volume didn't matter, we'd never calculate with port length.

It's not about volume - it's about the ratio of crossectional area to length. This produces a resistance that behaves like a mass attached to the springy air in the enclosure.

If you calculate different lengths to diffrent port sizes so that the volume is the same, they will all have different tuning frequencies. Again, it's not about volume.