Vent length question?

[NyxOne]

Disclamer : the following question might be offensive for advance user. Please do not read to avoid brain injury!

Hi,

i've a very very simple question, what happens when you double the number of your port for a given design ?

E.g. :
- Vb : 37 liter. (~1.3 cu.ft)
- Fb : 37 hz
- Vent size : 2 inch
- Vent length : 3.29 inch (estimated)

Now : When i double the number of vent, the length pass from 3.29 to 8.05.

Here is the question : Is this new vent length for BOTH of the port or splited in HALF Between the two port.

Very simple question, i know, but i've been unable to find the answer anywhere ...



Thanks
---------
Chuck!

[minkuni]

The length is for each port. Increasing the number of ports and keeping everything else the same means you have to use longer ports.

[NyxOne]

Thanks for the quick answer!

I got one last question :

Is there any drawback/advantage on using a single port vs 2 small port ?

Eg.: 1x3" VS 2x 1.5" ?

Thanks
---------
Chuck

[minkuni]

I do not feel that I have enough experience to give a good answer to that, but in most cases I would go for a single large port.

BTW a 3" has twice the area of two 1.5" ports

[augerpro]

Don't forget to use an end correction if the software you use doesn't already, otherwise the tuning may be lower than you calculated for.

[NyxOne]

I do not feel that I have enough experience to give a good answer to that, but in most cases I would go for a single large port.

BTW a 3" has twice the area of two 1.5" ports

Euh ? My maths are a bit far but are you sure ?

Area = r^2 \cdot \pi
((1.5*1.5) * 3.14159) * 2 = 14.12;

((3*3) * 3.14159) = 28.27;

Hummmm... you're right! Now i feel ashamed! ops:

Thanks again.

[NyxOne]

Don't forget to use an end correction if the software you use doesn't already, otherwise the tuning may be lower than you calculated for.

Hi there AugerPro,

How do you measure the end correction of the port ? There is alot of tuning port available on the market and none give seems to give that spec.

Thanks
---------
Chuck

[augerpro]

How are you calculating the port length?

[NyxOne]

How are you calculating the port length?

with a tape ... so i guess it's the same for the end correction ...

Thanks

[augerpro]

Do you have an existing speaker that you are modifying to use two ports instead of one? Or are you designing a box that you will be building in the future?

[NyxOne]

Do you have an existing speaker that you are modifying to use two ports instead of one? Or are you designing a box that you will be building in the future?

I've have an existing speaker and I've made it tall and narrow. I'm using 2 HiVi d6.8 in a 37 liter volume and I'm targeting a tuning of 33hz-37hz.

I currently have ~ 8" of clearance for a tuning port and my vent have a 2" diameter with one flared end .

I have "Chuffing" problem at high SPL (and probably port compression). V. Dickanson recommend using a tuning port with a diameter of 3" for 7-8 inch woofer. So having only 2" is certainly not enough

I'm tring to find a way to suppress the "chuffing" by using a vent with a larger area but without using an elbow ...

Unfortunately, i don't have many options due to the fact that i don't have alot of room/clearance for a long tuning port... (3") or two smaller diameter tuning port.

I'm considering using a 2" inch Precision Tuning port... or if don't have any choice a 3 inch with an elbow...

That's the whole story!

If you have any suggestion, i would be glad to hear it!

Thanks again!
-----------------
Chuck

[1Michael]

The 3" with an elbow will work fine.

[Eton]

http://82.95.237.142/mhsoft/PortLength.asp

[NyxOne]

The 3" with an elbow will work fine.

I know it will work. My problem is that I'll have to work with PVC tubing and i haven't found any that fit with my current 3" port trim. I'll have to take a better look

http://82.95.237.142/mhsoft/PortLength.asp

Thanks for the link but i don't think I'll use it. I usually take UniBox and/or WinISD when i want to find the best port size/length. They do the trick pretty well


Thanks everyone
---------
Chuck

[augerpro]

Ok, if you are using those programs they already include an end correction. I like unibox for this since it adjusts the end correction depending on flared/unflared ends and wall covering/stuffing.

[norcad]

I know it will work. My problem is that I'll have to work with PVC tubing and i haven't found any that fit with my current 3" port trim. I'll have to take a better look



Thanks for the link but i don't think I'll use it. I usually take UniBox and/or WinISD when i want to find the best port size/length. They do the trick pretty well


Thanks everyone
---------
Chuck

Just cut your 3" pipe with a 45 degr angle, and melt them together (glue and PVC are often difficult) to make a 90 degr knee. Even though you get a sharp angle inside the port it works real fine.

[NyxOne]

Just cut your 3" pipe with a 45 degr angle, and melt them together (glue and PVC are often difficult) to make a 90 degr knee. Even though you get a sharp angle inside the port it works real fine.

Excellent idea!

I'll try it tonight and give you some feedback afterward.

Thanks.
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Chuck