That's strange, adding a stem in the center of my port decreased the tuning about 1.5Hz. Anyway what your are describing will be very close to what I have done, although I found no acoustic benefit of the wave-guide on top except for a cover over the port and it made a nice shelf if I should decide to put something on top. Since your almost there why not make it closeable so you can have it both ways, Vented or Sealed, I found this to be of greater advantage then I ever thought it would be, music sounds great in the Sealed mode.
What I was referring to was the existing 135l project that has a 3.5" tube in the middle. Making it smaller won't help. What were you referring to?
Since your center piece is very small compared to the port, I would say it contributes very little to lower tuning, and that the whole assembly is what lowers your tuning, however minimally. Here is what I think, having played with it a little.
Your flairs, on the large port would need to be larger, and the wave guide lowered further into the port for it to be a more effective "tuning" device. With yours, I picture a lot of "termination" occurring right at the port edge, by virtue of the small roundover size. By design, air is to have a uniform cross section as it emerges from the port end and into the waive guide, where it still has a considerable distance to travel, decreasing velocity as it exits. When the air still has a significant distance to travel (large in relation to the cross section of airflow) in the curvature, more "tuning" is taking place. You want your roundover big, like 2-3 inches radius and adjust the numbers on the waiveguide assembly to suit the spreadsheet.
Adding a center connector, remember, adds drags, speeds up the air in the port to higher mach numbers, etc. This is a measure that enhances tuning with large resistive consequences, I believe. So I have shifted gears a bit to try to get an alignment that is close to desired tuning without the powerport, and then use the velocity reducing waveguides only, to not only lower tuning but as a noise reducer.
I bet if you do an experiment, you can verify my point. Your tuning should decrease marginally, 1 HZ or less by cranking the waveguide down. But because this is going to be a restriction on air, use test tones on very low volume to test this, as the consequential port compression will work against you to raise tuning (speculative).
As far as making mine moveable, I don't see feasibility in it. A seal would need to be used so it is not a leaky box, the same seal would interfere with flow during ported ops. Plus I may be mounting the waveguides to a glass top.
Since your center piece is very small compared to the port, I would say it contributes very little to lower tuning, and that the whole assembly is what lowers your tuning, however minimally. Here is what I think, having played with it a little.
Your flairs, on the large port would need to be larger, and the wave guide lowered further into the port for it to be a more effective "tuning" device. With yours, I picture a lot of "termination" occurring right at the port edge, by virtue of the small roundover size. By design, air is to have a uniform cross section as it emerges from the port end and into the waive guide, where it still has a considerable distance to travel, decreasing velocity as it exits. When the air still has a significant distance to travel (large in relation to the cross section of airflow) in the curvature, more "tuning" is taking place. You want your roundover big, like 2-3 inches radius and adjust the numbers on the waiveguide assembly to suit the spreadsheet.
Adding a center connector, remember, adds drags, speeds up the air in the port to higher mach numbers, etc. This is a measure that enhances tuning with large resistive consequences, I believe. So I have shifted gears a bit to try to get an alignment that is close to desired tuning without the powerport, and then use the velocity reducing waveguides only, to not only lower tuning but as a noise reducer.
I bet if you do an experiment, you can verify my point. Your tuning should decrease marginally, 1 HZ or less by cranking the waveguide down. But because this is going to be a restriction on air, use test tones on very low volume to test this, as the consequential port compression will work against you to raise tuning (speculative).
As far as making mine moveable, I don't see feasibility in it. A seal would need to be used so it is not a leaky box, the same seal would interfere with flow during ported ops. Plus I may be mounting the waveguides to a glass top.
The 135l stuffed box tunes as follows:
Bottom waveguides and flairs only: 26HZ
After adding top wave guides and center pipe: 24HZ
Predicted w/o any waveguides (conventional): 33HZ
Now the bottom waveguides aren't pointed like they would be if designing for waveguides only. Lots of suuden air acceleration, decceleration and turbulence. I speculate that getting 7 HZ of tuning from this alone may be because it is probably very resistive. I doubt that that could be obtained with spreadsheet designed waveguides with no center connector. But still, this illustrates how effective just one can be.
Bottom waveguides and flairs only: 26HZ
After adding top wave guides and center pipe: 24HZ
Predicted w/o any waveguides (conventional): 33HZ
Now the bottom waveguides aren't pointed like they would be if designing for waveguides only. Lots of suuden air acceleration, decceleration and turbulence. I speculate that getting 7 HZ of tuning from this alone may be because it is probably very resistive. I doubt that that could be obtained with spreadsheet designed waveguides with no center connector. But still, this illustrates how effective just one can be.
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I am wondering, what drivers out there, 15 or 18, might benefit from this extra port area? I am liking the way this project is turning out, and thinking of making more enclosures.
150-200 liter box with sub 20 tuning?
Any inexpensive drivers out there that would find a good home in a ported box such as this, especially a low VAS 18" maybe?
150-200 liter box with sub 20 tuning?
Any inexpensive drivers out there that would find a good home in a ported box such as this, especially a low VAS 18" maybe?
Sonotube water heater sub with 1804 at the bottom and powerport at the top (it would look like two plinths, one at the bottom and one at the top, but the top one will have the powerport instead)
Or don't use a powerport altogether and then have a sealed dual 1503, with one at the top and one at the bottom. I've seen it done, and I imagine it would be awesome. LT if necessary.
BTW, the AL1804 uses a nicer basket than the 1803 did.
Or don't use a powerport altogether and then have a sealed dual 1503, with one at the top and one at the bottom. I've seen it done, and I imagine it would be awesome. LT if necessary.
BTW, the AL1804 uses a nicer basket than the 1803 did.
Been there, done that, and yes it is awesome. Tube-Zilla
An externally hosted image should be here but it was not working when we last tested it.
Michael
It, like the AS-15, is gathering dust in storage, since I only use my 2 IB's.
But yes when it's actually installed someplace (vacation home) Tube-zilla will need a LT circuit and a HUGE amp. It's really inefficient given the small enclosure....
I don't create LT circuits until I can measure the sub where it's going to be operating, since room gain isn't all that predictable
It, like the AS-15, is gathering dust in storage, since I only use my 2 IB's.
But yes when it's actually installed someplace (vacation home) Tube-zilla will need a LT circuit and a HUGE amp. It's really inefficient given the small enclosure....
I don't create LT circuits until I can measure the sub where it's going to be operating, since room gain isn't all that predictable
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