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

[seanzozo]

Looking at the sheet, The rule of thumb for lowering the terminus actually is essentially dead on (generally well into the noise floor of the accuracy of any woodworking tools) for any BIB that actually looks like a BIB. Really was just was enjoying some fun geometry.

The neat thing about the BIB is how simple the calculations are and how resilient its behavior is to changes in shape and to estimation.

Sean

[JORGETronic]

Hello

Well, the Hemp acoustic FR8 arrived yesterday, dimensions I get for them in this tread were:

10" (W) x 17" (D), BiB height would be 70". The internal baffle will be 71/2" away from all the walls, is this OK?
Unfortunately this dims were no yet included in the http://www.zillaspeak.com/BIB
Thanks!!!

[Godzilla]

Perhaps Scott will 'BIB up the Hemps'... I think he's planning too.

Be patient...

you need the .asp for the page to load...

http://www.zillaspeak.com/bib.asp

Peace,
Godzilla

[jimmyd53]

Jorge,

Check post #140 on this thread. GM changed the cross section of a BIB for the Hemp FR8 to 303in^2. This results in a very large enclosure. Good Luck.

James

[JORGETronic]

Jimmy Godzilla, thanks for your prompt response

The main point here is that I have the speakers, my wife will be travelling this week end, so I will be alone with my 3 kids, if I have the dimensions I can build the boxes, the equation is very simple:

Kids + wood + speaker + no wife = Paradise

Checking posts as Jimmy suggested:

If section is 303"^2…….so W= 18", D=17", H= 70" , Driver= 39" from the bottom, I will continue reviewing the GM notes

Thanks again!!!

[fred76]

Originally posted by seanzozo


The spreadsheet was a quick and dirty effort to make sure that I was close. It (as GM mentions) ignores the width of the center baffle. Those lower numbers are portions of the final calculation. The path is defined by two parallel lines (down and up) and a semicircle at the bottom that joins them. The numbers determine the radius of the semicircle, from that the path-length of the semicircle, from that the remaining line length that needs to be split between the down/up diagonal path sections, from that the vertical displacement of these diagonal portions, from that total height. The calculation was done in multiple pieces to make sure that results were reasonable, easy to check and to debug if my calcs were off the first time.

The result though seems to be that unless you are working with a giant honking box that just calculating Line-length/2 is more than adequate.

Sean

Sean,

A friend explained (to me) the formulas you provided in the spreadsheet through a diagram, particularly the ones that concern the Semicircle. I came up with this 'color coded' illustration for a visual representation. *Again, borrowing from "lovechild"'s original side view diagram*



If the Internal Baffle Thickness is to be taken into account, then the Semicircle Radius would be much more precise. Although, it makes very little difference in the final outcome. The spreadsheet is quite useful for those who are not deterred by drivers that would require a large Sm.

fred

[oface]

Hello all,,

I finally finished my bib's using the fostex 166e drivers.

The dims ( all outer, in inches) are this.

72Hx12Dx9.5W,Drivers are about 34" from the top.

I came up with these dims on the fly before godzilla had posted up his very helpful site, I know they abotu 8" too long, and maybe the driver a little to high according to what is posted on the site ,, but lemme tell ya ,, they sound really great ,, nto the end all be all, but for the coin ,, not too shabby at all



I had to mount a baffle on the front to give the magnet space in the back,, I felt there wasn't enough breathing room .

The cabs are made out of 3/4 mdf, like the bk-16's I made, I wanted to do this on the cheap ,, and to see how they sound,,

Well I am very impresed and surprised with the output of this setup now.

I started out with br boxes, then went with OB's ,diy bk16's , and now these BIB's.

Been listening for about the past 3 days/nights with a lot of different material,, now I am not saying the will pump out metallica at concert levels, but for my tatstes and levels I am really impressed....

So thanks to you guys for bringing back this design into everyone's attention, TC, scott moose, GM, godzilla and dmason..

Now it will be time to tweak , and look for some nice lumber to make some really nice cabs out of,, any suggestions on some nice wood?? maybe some kind've tone wood?? basswood??


Also been wondering what about a MtM version of these ?? ideas anyone?

[oface]

Oh yeah ,,

When I figure out how,, I plan on posting pics.

later,,


chris

[Scottmoose]

A good quality pine is usually good for horns, or so I understand. If you've got the cash / facilities, you could do worse than following TC's lead: alder or Far Eastern Maple. Otherwise, a good ply is always nice. I like the Finnish birch myself, as it looks great just by itself -I like the natural appearence of plywood, especially with a few coats of clear polish or varnish. The edges look especially nice.

I hate to be a heretic though, but I still find MDF works pretty well with these cabinets. Not as good as the others, but it still works well enough for you to enjoy them. It's not quite as natural sounding, but it's not bad either.

Hemp FR8?

Well, Greg made some optimum suggestions quite a few pages back which were much better than my early ideas. However, here's a further thought -I actiually like the look of this one quite a bit. It doesn't quite match the response curve of TC's original, but it keeps the cabinet size relatively managable (that's why, if anyone's wondering, the response of the suggested dims I made for the Monacor SP-200X 8in driver on Jeff's pages look different to most of the others -you'd get better performance out of a larger cabinet, but I wanted to keep the size down. Also, I wondered if a monster enclosure would be worth the effort for a cheap driver, good though I'm sure it is.)

200in^2 terminus. 150.5in line length. Driver 30.1in from sealed end. Me, I'd do 10in wide x 20in deep (internal). Paint it satin black, have a bit of a polish / varnish, and hang a model of Discovery from 2001: A Space Odyssey between them. OK, so the proportions aren't quite 1x4x9...

Regards
Scott

[Scottmoose]

Couldn't resist it. Just for fun, the Hemp FR8 Monolith, inspired by Stanley Kubrick's & Arthur C. Clarke's 2001: A Space Odyssey.

Flip the enclosure sideways, so it's wider than it is deep.

1x4x9 external dimensions (excluding the plinth).

8in deep. 32in wide. 72in tall. Driver 28.75in from the internal sealed end. Terminate the internal baffle 14.875in from the internal base, and the internal left and right side walls. 1/2 space response is very similar to the one above, as you can see. Strauss is advised to run the drivers in.

Please note however, it must either be painted satin-black, then suitably polished, to tie in with the film, or made of transparent acrylic, to tie in with the book. Also -no rounding off of the edges! They must stay sharp. Or I'll send the boys round

Yours in good humour
Scott