Determining port area

[Decaf]

Read the vance dickason port method, and you will have a greatly tuned enclosure.

uve mentioned that twice yet wont state the method.

for those who dont know its from the loudspeaker design cookbook, and does not always work either

dv=diameter of vent

vd=sd*xmax <<<<<needs to be accurate

fb=tuning frequency

[RAM_Designs]

^^^what is the length supposed to be? Or do you just need to figure it out yourself after determining the port area that you "should" use?

[herbykw]

How does it work with multiple subs? If I did this correctly dv = 18,956.88. I am using 4 subs.

[Decaf]

^^^what is the length supposed to be? Or do you just need to figure it out yourself after determining the port area that you "should" use?

your're suppose to figure out length after that.... this is not a method I use. i just noticed bcarter mentioned vance dickason 3 times without stating what the formula was/the issues with it

richard small (neville thiele+richard small = theile/small paramaters, or tsp's commonly) suggests a more conservative equation, but its similar

most people know this formula from carstereo.com, the minimum port area calculator. it is known to suggest WAAAAAYYYY too much port area in most cases. the answer is given in a diameter also, so the issue with that is a circle port of say 50sqin =/= 50sqin slot port. they will not act the same with identical volume and it doesn't account for flared circular ports

How does it work with multiple subs? If I did this correctly dv = 18,956.88. I am using 4 subs.

either your math is wrong or therein lies the problem. it will suggest diameters that are non-existent/not applicable in a car audio

[Mha]

Get 3" tubes and a 3"terminal cups drill holes till it sounds good. If you over do it fill them in with the terminal cup

[bkolfo4]

Carstereo.com is not too big - that is what is required for a port that operates 100% correctly. The correct statement would be "most people use much less than what would be the perfect size, since it is hard to fit them into a small car box".

Notice those formulas do not say anything about box volume. Port area is not related to box volume. That was started as a very general guideline for people that do not want to take the time to determine what they actually need. . .

[bkolfo4]

I used Autocad. I drew a 6" circle and then did did a properties of it and it gives me the area. and then I multiplied it by 2 for two ports and then divided it by your box volume. odd information about circles. whenever you double the size of a circle say 2" dia to a 4" dia you have 4 times the area.

So 1 - 4" circle is the same as 4 - 2" circles

Area of a 2" circle is 3.1416

Area of a 4" circle is 12.5664

The area of a circle is 3.14159 * radius^2

Note your example above, while (4) 2" tubes would have the same area as a single 4" tube, the port length would not be the same given the same net volume.

[Decaf]

to operate 100% correctly at xmax.

most subs rarely see xmax through the variety of notes played so u can get away with less port area... dependent on power of course

[bkolfo4]

Definitely depending on power. But I find car audio is where people try to run the most power and use the least amount of port area.

I see more subs damaged mechanically than thermally when used in cars. . .

I should add - many times the mechanical damage is from playing below tuning, but the point is still most car setups I see have no problem taking the sub to the mechanical limits, even above tuning.

Brian

[herbykw]

Can you please correct me where I'm screwing up.

Start with SD 201.93 multiply it by xmax 16.5 which gives me VD of 3331.84.

3331.84 times 411.25 = 1,370,221.26. I then devide that by the square root of FB 35 which is 5.91.

1,370,221.26 devided by 5.91 = 231,847.508 to the 0.5 power = 481.5055 times 39.37

Total outcome 18,956.87..

I will be pushing these four DC lvl 2 8"s with a DC 2k.