Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks?

[xrk971]

It is probably an air leak at the bottom cap. I will try sealing with plumbers putty before gluing. Everything says it should work, it must be the seal...
Should be monster bass if it works.

[GM]

Originally Posted by Squeak

Idealy a BiB should be pushed in a corner or at least have some half-space boundary loading, like ceiling and wall.

Positioned out in the open on a wall is considered 2pi [half space] loading:
True Audio Speaker Topics: Spatial Loading

GM

[GM]

Originally Posted by xrk971

It is probably an air leak at the bottom cap. I will try sealing with plumbers putty before gluing. Everything says it should work, it must be the seal...
Should be monster bass if it works.

I guess I missed something....... how do you know it will have a lot of bass in 1/2 space? BIB requires at least 1/4 space loading AFAIK to protect the driver somewhat below Fs.

GM

[xrk971]

My past experience with a BIB is that there is plenty of bass. Would mounting on a wall with mouth aimed at ceiling (3 ft away) count as 1/4 space loading?

[GM]

As it should if at least up against a hard wall and at least 6 ft tall [~12 ft path-length] with an 8 ft ceiling; but yours is only around 5 ft, so no, 3 ft away is probably going to net you nothing in 1/4 space.

GM

[Squeak]

Originally Posted by GM

I guess I missed something....... how do you know it will have a lot of bass in 1/2 space? BIB requires at least 1/4 space loading AFAIK to protect the driver somewhat below Fs.

GM

Just a little OT question: When you talk about protecting the driver in this way, as you often do, you don't mean the resistive pressure actually stopping the driver from moving?
Rather you're saying that you don't have to EQ it so much to get the same bass, and thereby protecting the driver from over-excursion at peaks?
Am I right?

[xrk971]

I think that the resistive pressure is what GM is talking about, although I don't see how a BIB with it's expanding wide open geometry and lack of a throat could ever develop enough resistive back pressure to limit cone excursion, although, if tuned to have resonance at correct frequency near excursion limit it could work.

[xrk971]

Originally Posted by xrk971

It is probably an air leak at the bottom cap. I will try sealing with plumbers putty before gluing. Everything says it should work, it must be the seal...
Should be monster bass if it works.

Ok, good news, it was an air leak on the bottom cap. Once I sealed it, it sounds great! Nice bass and it couples to the wall very nicely. I had to line the flat surface behind the driver with a layer of open cell foam and added more stuffing into the triangle cavity above the driver. This improved the tightness of the bass. Less boomy. Anyhow, it was a good result and I am now proceeding with the second unit build.

[Squeak]

Originally Posted by xrk971

I think that the resistive pressure is what GM is talking about, although I don't see how a BIB with it's expanding wide open geometry and lack of a throat could ever develop enough resistive back pressure to limit cone excursion, although, if tuned to have resonance at correct frequency near excursion limit it could work.

My thinking exactly. The resonance effect would be quite weak and only work within a limited window.
Think of a long spring where a wave started at one end has to travel all the way to the end and back again. At some frequencies it could even make the problem worse.

[kec]

Xrk,

What final dimensions did you use? External and internal.