Trying to understand a particular box design

[Goldtaz1 10+ year member]

Well, that's the argument. JMac says the waves will cancel each other out. Others say the wave will combine. Right now, noone on this board has the technology to figure it out.
You'd basically have to trace the air pressure wave from the sub to the intersection and out the port. Even then, you're going to find that different frequencies will have different amounts of cancellation.

My theory: It'll work, but now you're looking at a second tuning frequency based on the width of that port. I have no idea how long a 30hz wave is opposed to a 60hz wave, so you're on your own there.

That's a box tuned to 30hz grand with a 53hz bend for that extra kick. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

I'm not sure I follow your last comment. My understanding of a ported enclosure is that you tune to ONE tuning frequency and that bends in a port length are done to achieve the port length at a given tuning frequency. I am going to go to an engineering buddy of mine and see if he can provide some scientific evidence of cancellation or a combination of waves.

 

[pooksta]

Hopefully, first of all, the subs are getting the same signal (mono). This would be the first way to avoid cancellation. Adding the wave guide (the little part where the port splits) may help, but probably not noticeably. If the subs are putting out the same signal, then their output should sum where the ports come together. I'd recommend running a test if you have an SPL meter, build the box with a couple of variations and see what works best.

 

[Raven 10+ year member]

^ Agreed.

As for the "dual tuning", well, ignore it. I'm thinking pretty 2 dimensional. First things first, this is just air pressure. Up wave is high, down wave is low.

Theory A:

If two high waves meet, they could possibly reflect each other, and immediately go back to occupy the low pressure space immediately behind it. The top wave will strike, cancel itself out, AND affect the backwave. Uber cancellation occurs.

Theory B:

You make the entire box a high pressure zone (back wave) and the air has to go somewhere. So whats it do? Since both sides of the enclosure have an equally high amount of pressure, the air goes out the port, where there is less air pressure and more empty space to occupy. The front wave occurs, and the exact opposite happens, you make a low pressure zone, so air rushes in to fill the space, and divides evenly between the two equally depressurized chambers. Cancellation is neglegible.

Overthought this yet? Here's Chubby's take:

During the back wave, the excess pressure races for it's only exit (again). Rather than getting stuck in a corner and creating turbulence, it bounces off the corner block at a nice angle. Now in the port, the second bend it hit the same way. It' only at the end that both waves meet, and they're now both going in the same direction, so they naturally combine.

Yay, I'm bored.

END Self proclaimed expert mode; Wheeeee.

 

[Goldtaz1 10+ year member]

Thanks a bunch for your help Raven. Hopefully I can take what I've learned here and do some testing and just see what works and what doesn't work.