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The BIB Pipe Project - Advice Needed
The BIB Pipe Project - Advice Needed
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Old 1st July 2020, 11:47 PM   #11
Hitmanray is offline Hitmanray  United States
diyAudio Member
Join Date: May 2020
Evening All

Thanks again for the feedback. Couple of answers to specific questions/comments raised.

The intrusion of the coupler from the outside to the inside will reduce the cross-section of the outer-pipe...
Absolutely. I actually accounted for this in my original concept by increasing the overall diameter of the outer pipe in the section where the driver box was located. I had to google how to calculate the area of a segment of a circle (long time since my school days) but was able to find the overall increase in ID was not actually that much to account for the area being consumed by the driver box. I then used an approximation to curve the ID back to the point where the driver box finished. You can see the effect as a bunch of circles if you look at the bottom view of the driver box in my original post.

Are you even sure you need the fold?
Nope, not sure at all. The only thing I have guiding my choices on line length was the BIB calculator spreadsheet. I do like the idea of linking the line length to the fundamental resonance frequency of the driver as it "makes sense" to me, but have no grounding in the science to know if it could be longer or shorter.

Based on the feedback and an attempt to read to Martin King's Quarter Wave Speaker Design info (of which I would say I probably comprehended a good 30%) I have come up with the following changes to iterate the design.

Remove the taper from the back of the driver box. Project rear of driver box to cross entire diameter of outer pipe. The thinking here was based on looking at some of the back loaded horn designs which have a driver box with a relatively small transition (cross-sectional area wise) into a horn (or in some cases a TL). By running my cone through the middle of the driver box what I effectively end up with is a expanding open TL (not expanding to horn proportions) from the bottom of the driver box, and a short closed tapered TL from the top. I did note the comment that the short line is probably not doing a lot sonically. The primary reason for keeping it is to provide the taper effect in the top section of the outer pipe (and I've grown to like it from an aesthetics perspective).

The thing this does do is require a much more aggressive flare of the outer pipe around the driver box to maintain the cross-sectional area of the outer pipe at this point in the line. That again should be fairly easy to design with a little geometry tinkering and CAD work.

I have attached a couple of pics of what I think this could look like. The flare in particular will need a lot of work and I think could end up looking much more spherical in nature. Will need to run some number of cross-sectinoal area consumed by the driver box.

Couple of questions/thoughts:

1) If using this driver box approach (as employed in BLH design) is there any guidance around box volume or minimum dimensions of the box?
I've looked at lots of designs and some of the driver boxes are quite small with the rear panels being very close to the back of the driver, but can't see anything to provide guidance on size.

2) What is the best shape for the back of the driver box?
Most obvious choices would be completely flat or following the curve of the outer pipe. But given this piece will be 3D printed I could do something more exotic. Perhaps a saw tooth deflector (something I have seen in some BLH) or an egg crate style. I could even open it to the rear and simply have an open stuffed tube (like the LX mini driver pipe). I guess the goal here is dispersion or absorption of the back wave. Perhaps this is something I could make a few designs and experiment (once the main concept has been proven).

I really appreciate the feedback from the community. There have been a few posts suggesting attempting to build something simple and go from there. I appreciate the approach, but honestly I am really enjoying the thought process of attempting to identify and mitigate the design flaws. I am an engineer by trade who has long been in a management role and I am finding the learning and design process really invigorating.

I also really appreciate some of the suggestions for different designs. I do like the idea of running the "inner" pipe down the side of the "outer" pipe. I am still hooked on the symmetry of the free hanging cone at the moment so not quite ready to give up on that one just yet.

Once again I appreciate all input. It's been a really enjoyable few weeks bringing these ideas together. But again, if anyone can see major flaws please let me know.
Attached Images
File Type: jpg BIB Pipe 2.0 Inner.JPG (24.8 KB, 36 views)
File Type: jpg BIB Pipe 2.0 Outer.JPG (22.7 KB, 37 views)
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Old 2nd July 2020, 01:21 AM   #12
planet10 is offline planet10  Canada
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Join Date: Oct 2001
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The BIB Pipe Project - Advice Needed
You could solve a lot of problems if you turned you line inside out.

Stay safe. Stay home. Respect the 2m bubble.
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Old 2nd July 2020, 02:45 AM   #13
Hitmanray is offline Hitmanray  United States
diyAudio Member
Join Date: May 2020
You mean like this?

I laughed when I first read your comment but I think you might actually be right.

The only challenge I can see is that at the Zdriver distance from the top there would only be about 6.5mm between the ID of the outer pipe and the OD of the inner cone (based on some quick rough calcs). So I would need to build the driver out from the pipe a bit.

Need to think about that one some more.
Attached Images
File Type: jpg BIB Pipe Inside Out.JPG (32.3 KB, 30 views)


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