aero/round port bend question.

[CHEMMINS 10+ year member]

Ok....scenario time.

Say you need a round port 30" long. From the mounting surface you have 25" before you run out of room and have to put a bend in. 6" round port.

How do you calculate the bend for length to achieve the overall 30" needed for chosen tuning?

Click to read more...

 

[Seriously_Tho]

OK, problem #1 is you're asking an intelligent question. Stop that.

Prob #2 - I don't know jack about porting, I use sealed boxes. But it seems like the parameters of your design software might be off, like maybe it thinks your box is deeper than it is. The theory with porting is the port should only vent the backwave after reflecting off the rear surface opposite the sub. Putting a bend in there seems like it'll monkey stuff up.

If all else fails, use a flexible dryer duct //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[CHEMMINS 10+ year member]

Lol.....nice.

Yes I know its an intelligent question. And the example I gave was a totally random example, it is more for the theory. Also guys bend/corner slot ports all the time. But with a round port you experience more swirl than you would in a slot or square port. Any bend is going to give you pressure drops in the corners, I would like to know if there is an actual math calculation to effectively make a port with a 90 as efficient as a straight piece.

 

[Seriously_Tho]

A-ha, the double-helix port propagation model, very nice. Should have great genes.

 

[audioholic 5,000+ posts]

A bend in a round port is measured by calculating through the center of the bend. The actual length the bend will add to the over all port length will depend on the diameter, the radius of the bend (measured in the center), and the length of the bend.

 

[James Bang 5,000+ posts]

There is no such thing as a stupid question.

 

[Buck 5,000+ posts]

A bend in a round port is measured by calculating through the center of the bend. The actual length the bend will add to the over all port length will depend on the diameter, the radius of the bend (measured in the center), and the length of the bend.

x2.

 

[helotaxi 5,000+ posts]

Prob #2 - I don't know jack about porting

Stop there.

The theory with porting is the port should only vent the backwave after reflecting off the rear surface opposite the sub. Putting a bend in there seems like it'll monkey stuff up.

Not hardly how it works. It's based entirely on pressure and inertia of the air in the port changing the pahse relationship between the driver and the port outputs and has nothing to do with backwaves reflecting.

 

[CHEMMINS 10+ year member]

Alrighty....was wondering when you were gonna pop in here.

Is there a way to calculate for the low pressure and change in inertia because of the bend vs the straight to compensate and arrive at equivalent tuning?

 

[audioholic 5,000+ posts]

Alrighty....was wondering when you were gonna pop in here.
Is there a way to calculate for the low pressure and change in inertia because of the bend vs the straight to compensate and arrive at equivalent tuning?

Adding a bend, if measured correctly, will not alter tuning versus a straight port. The biggest mistake made with ports these days, even by 'experienced' people, is placing the mouth of the port too close to the driver, which doesn't allow the interior volume of the enclosure to properly/completely pressurize before exiting the port (or entering it, depending on the direction of cone excursion atm). This will, in effect, lower the perceived internal volume of the enclosure, altering tuning.

 

[skylineTT 10+ year member]

Audio, I designed a big ported box tuned to 30 and it said that if i were to use a 3" diameter port, it would have to be 3 inches long to keep 30hz... is this not wrong somehow? i feel that a port that short would act as a hole in the box. been wondering about it for a long time.

 

[James Bang 5,000+ posts]

Audio, I designed a big ported box tuned to 30 and it said that if i were to use a 3" diameter port, it would have to be 3 inches long to keep 30hz... is this not wrong somehow? i feel that a port that short would act as a hole in the box. been wondering about it for a long time.

that's a 4 cuft box... you might want to up the port diameter to minimize port noise

 

[Seriously_Tho]

Stop there. Not hardly how it works. It's based entirely on pressure and inertia of the air in the port changing the pahse relationship between the driver and the port outputs and has nothing to do with backwaves reflecting.

It's funny to think what internet forum people would be like in real life.

 

[skylineTT 10+ year member]

so if i did a 6" or 2 6" aeros, it should lengthen them a good bit right?

 

[James Bang 5,000+ posts]

yes 17"