Wan to make a 3 cubic foot subwoofer sealed but want sonotubes for ttl loading and add to dox volume. Google el Pipo on Nelson pass’s site.

[Pogre]

As I indicated in my previous post, the tuning tube for an 18 Hz frequency would have a total volume of about 7 cf for a 6 inch pipe.. So a straight 6" pipe would have to be about 8 feet long.
The law of physics is inflexible. If you use a smaller diameter pipe, it would need to be shorter but you would risk getting shuffling noise at infrasonic frequencies. That of course depends on the SPL you would demand from the sub driver.

How long would it need to be for his plan to add it onto his existing sub?

 

[Verdinut]

First thing you wanna do is figure out what diameter you want and settle on that. Then you can start plugging numbers. The bigger the diameter, the shorter it'll be.

For a tuning pipe, the bigger the diameter, the longer it has to be.

 

[Verdinut]

How long would it need to be for his plan to add it onto his existing sub?

Well, it all depends on the pipe diameter. According to my calculation using BassBOX 6 Pro, a 6" pipe would have to be about 8 ft long. That is for a tuning frequency of 18 Hz.

 

[ryanosaur]

I don't know how the coupling chamber changes things, but the 1/4-wave tuning of a straight 20Hz pipe would be just a hair over 14' long.
For the diameter of the tube... again, I cannot say if the dia of the tube is equal to the diameter of the cross sectional area of the drivers Sd, or if the tube just needs to have a dia large enough to avoid chuffing.

 

[Verdinut]

I don't know how the coupling chamber changes things, but the 1/4-wave tuning of a straight 20Hz pipe would be just a hair over 14' long.
For the diameter of the tube... again, I cannot say if the dia of the tube is equal to the diameter of the cross sectional area of the drivers Sd, or if the tube just needs to have a dia large enough to avoid chuffing.

In my opinion, we're not talking here about a TL. Therefore, the 1/4-wave tuning does not apply. With only a pipe hanging out, it's still a bass reflex box. Instead of having the port or duct within the box, it's outside.

 

[ryanosaur]

In my opinion, we're not talking here about a TL. Therefore, the 1/4-wave tuning does not apply. With only a pipe hanging out, it's still a bass reflex box. Instead of having the port or duct within the box, it's outside.

Yes, this could be tackled in a few ways...

If you read the article I linked By Kent English and Nelson Pass they clearly describe El Pipe-o as a transmission line, and by all accounts it matches everything else I've seen in the category of a TL utilizing a Coupling Chamber.

Yes, you can achieve a Vented box using external vents as you describe. It might be easier to break them into two shorter pipes, also.

Is one better than the other? (I think that's a loaded question!)

Yet @CajunLB specifically asked if it would be possible to turn his existing subwoofer, a 15" Dayton Ultimax in a sealed 3cu.ft. box, into an El Pipe-O.

Frankly, I think with the right amp and DSP, he can achieve some decent infrasonic behavior with what he has... how loud?, I cannot speculate, but that driver is designed to be pushed more like the modern Pro Driver Sub builds are.

Regardless, my skills aren't there for this... I've spent a lot of time looking at all of this lately for myself and I am still learning how to apply all of this.

For an El Pipe-O, Transmission Line with Coupling Chamber, conversion, the only person I can think of here that can answer whether it could work is @TLS Guy , if he would be willing to help our friend @CajunLB out.
Again, for anybody that didn't see it the first time, the English-Pass article:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiuwv6LsN7vAhVVnp4KHb_-DikQFjAAegQIDhAD&url=https%3A%2F%2Fwww.firstwatt.com%2Fpdf%2Fart_elpipeo.pdf&usg=AOvVaw3KOpGoQhdXsoB7ZpDS4kna