Port size

[quindecima]

I am in the process of building a pair of the 4351 speakers. I don't have any 5 3/8 cardboard tubing nor know where to get any, I do, however, have a bunch of 4 in. tubes from my 4345 build. Can anybody give me an idea of how many and what length I should use? I was thinking 4-6 would do it.

[Doctor_Electron]

I am in the process of building a pair of the 4351 speakers. I don't have any 5 3/8 cardboard tubing nor know where to get any, I do, however, have a bunch of 4 in. tubes from my 4345 build. Can anybody give me an idea of how many and what length I should use? I was thinking 4-6 would do it.

Hello... If you take the sum of the port tube volumes of the 4351, using the formula [ volume = pi x (radius squared) x height ] where height is the tube length, then recalculate for the sum volume using the 4" diameter, this should work.

I'm not a math whiz so any pro or con input on this approach would be welcome and educational.

-de-

[Challenger604]

I am in the process of building a pair of the 4351 speakers. I don't have any 5 3/8 cardboard tubing nor know where to get any, I do, however, have a bunch of 4 in. tubes from my 4345 build. Can anybody give me an idea of how many and what length I should use? I was thinking 4-6 would do it.

Hi Larry,
Ask John, he will hlep you!

[Ed Zeppeli]

Hello... If you take the sum of the port tube volumes of the 4351, using the formula [ volume = pi x (radius squared) x height ] where height is the tube length, then recalculate for the sum volume using the 4" diameter, this should work.

I'm not a math whiz so any pro or con input on this approach would be welcome and educational.

-de-

I thought there was some sort of inverse relationship involved with ports. I'm not so sure it's as easy as making sure there's no net volume change.

I could be wrong.

[Ed Zeppeli]

You could try this...

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

[Horn Fanatic]

I am in the process of building a pair of the 4351 speakers. I don't have any 5 3/8 cardboard tubing nor know where to get any, I do, however, have a bunch of 4 in. tubes from my 4345 build. Can anybody give me an idea of how many and what length I should use? I was thinking 4-6 would do it.

You can take the guess work out of figuring out how much this and that you need if you work the problem mathematically. A vented speaker enclosure is basically a Helmholtz resonator. I take it you don't have speaker design software, such as Bass Box Pro to assist you? The goal is to resonate the acoustical reactance of the mass of air in the port, weather it be a vent or duct, to the acoustical reactance of the compliance of the air chamber, both reactive elements. The resonance being your tuning frequency, which should be the fs of your driver.

Leo Beranek wrote a section about calculating the parameters of a Helmholtz resonator in Part XIII pg. 131 in his book titled 'Acoustics'. It's quite simple. The down side is that the equations do not take Vas into consideration, but they should point you in the right direction.

IMO, Large vents are better than small vents. I typically use 6" diameter vents or ducts. They will provide a more solid articulate bass. Tubing of that diameter can be found at outlets that sell Sonotube, or you may try transmission shops that replace drive shafts. They are usually shipped in large cardboard tubes. Keep in mind. The larger the diameter, the longer the vent. That's how it works.

H.F.

[quindecima]

I'm using a port size of 4in. and 9.5 cu feet and a tuning freq of 290hz and the on line calculators give me a length of -2.8in????? that can't be correct

[Ed Zeppeli]

I'm using a port size of 4in. and 9.5 cu feet and a tuning freq of 290hz and the on line calculators give me a length of -2.8in????? that can't be correct

If you plug in JBL's specs does the port length jive with what JBL has in the speaker?

[quindecima]

If you plug in JBL's specs does the port length jive with what JBL has in the speaker?

Nope!

[Allanvh5150]

I'm using a port size of 4in. and 9.5 cu feet and a tuning freq of 290hz and the on line calculators give me a length of -2.8in????? that can't be correct

Probably. A 9.5 cu ft cabinet would be better tuned to 25 or 30 hz. I am not sure why anyone would try to tube a cabinet to 290hz.

Allan.

[quindecima]

Probably. A 9.5 cu ft cabinet would be better tuned to 25 or 30 hz. I am not sure why anyone would try to tube a cabinet to 290hz.

Allan.

I just came back to correct that. I used the JBL tuning freq. for the 4355 which said 290HZ thinking that was the correct one but in actuality it is more like 28hz

[Earl K]

Here are the port lengths needed ( just under 13", according to WinISD ) when a person chooses a quantity of 4, 4" inside diameter, round ports .



You really need to get yourself a ( free ) copy of WinISD so you can start to understand the relationship between a tuned box ( helmholtz resonator ) and the transducer driving that resonator .

[Challenger604]

I just came back to correct that. I used the JBL tuning freq. for the 4355 which said 290HZ thinking that was the correct one but in actuality it is more like 28hz

That's correct, 28 is what you would target for. You tune it with the length of the tube. Mine are 30 but I won't bother for something that I can't even hear.

The 290 Hz are the cards that you will need for your 5235. You will have an other setting inside the 5235 to set. It is important to have the right setting inside the 5235 as well or you can damage you 2235's...
C

[Doctor_Electron]

I thought there was some sort of inverse relationship involved with ports. I'm not so sure it's as easy as making sure there's no net volume change.

I could be wrong.

The plot thickens...

http://troelsgravesen.dk/vent_tuning.htm

-de-

[quindecima]

I downloaded winISD and glued in all the parameters and came up with a length of just over 10 in for two 5in. diameter tubes. It's things like this that make me glad I never became an engineeeeer.