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

[McFaBs]

Originally posted by copperhead
Hi Fab,

I got an internal depth of 17.58", internal baffle 8.79" from front back and base.

The internal baffle came out to 71.44" long. Your right the oblique angle is only a fraction

longer. 71.3" + 8.79" = 80.09". I was going for a heavier base on Scotts' suggestion.

I don't have any experience of marble or granite but it had seemed like a good idea.

Plywood is easier and cheaper.

John.

I see, I do a different calc.
L= 150.5 so H = 75.25
Circle radius = W/4= 17.58/4= 4.4(circa)
Semi circle lenght = 13.8"
Difference from L/2 lenght = L/2-[(W/2)+(SemiC/2)] = 1.89"
Effective lenght = L/2 + 1.89" = 77.14 internal.
Assuming the sloping line more or less equal, that measure is the same for both.
So internal corrected H= 77.14"

I think it works like this if I've not misunderstood GM and Scott suggestions.

Considering marble and granite, if you have some spare at home you can try. I don't know if they bahave with speakers like turntables instead, certainly they look sritking good, I know... I'm not going to try when I'll build my BIB because I will use the platforms I own which work preatty well.

Ciao.Fab.

[croat47]

Originally posted by Scottmoose

Try a line length of 67in, Zdriver 13.5in & terminus area of 25in^2

I have a number of B3S's around for various uses. Based on the MTM line of thought and the above starting point for the associated BIB:

2 drivers, 50sqin throat, same line length, and the Zdriver would be the center of the two drivers?

Hoping this will make a nice small room jazz/folk speaker for lower level listening.

Regards.

[copperhead]

Hi Fab,

Your right I did screw up the calculations. I blame years of watching reality tv and too much

alcohol. Really just carelessness. Thanks for clearing it up though, the box is big enough without

errors making it bigger.

Keep us updated on your progress.

Thanks again John.

[McFaBs]

Hi John,

yes, Hemp BIB are really big and should sound great! (according to GM thought in this post http://www.diyaudio.com/forums/showt...418#post990418)

You're luky to have place for a real BIB!

As far as I finished coating the wood floor in the basement I'll start to build my BIB, smaller, but hope it'll sound great either!

Ciao.Fab.

[GM]

Originally posted by ChrisMmm
.........I have a set of drivers/crossovers for a pair of Ariels (MTM) ...........that means doubling the mouth area...........double the volume.............

Length would stay the same for that driver??

Regards driver position...........would you use the mid point between the drivers?

Greets!

Correct.

Right.

Theoretically, yes, but shifting the driver 'module' a bit to make them fit shouldn't be a problem, and of course the XOs will be off unless you replicate the Ariel's baffle width/shape and place the BIBs well away from any walls/corners, negating some of its benefits unless floor loaded.

GM

[Scottmoose]

I reckon it'd need to be -it's not very tall. And 112in is the longest I'd try -I used the regular driver T/S parameters, suitably modified for there being two of them for the above sim, but I hear dark rumours that Fs is considerably higher than is advertised.

[GM]

Originally posted by copperhead
The height of my ceilings is only 94.5". As the walls and ceiling form the mouth of the horn, is there enough space for this to work properly?

Way back somewhere in this thread I thought it was decided that cab height was half line length [or at least pretty close]. But thinking back it may have been more a rule of thumb for smaller drivers.

Greets!

When you use the SQRT(2) width/depth ratio, the length is divided by 2.

My (lack of) math skills precludes me from calcing the optimal mouth/ceiling distance (I have to draw it out to scale ), but the ideal AFAIK for corner placement is that it ~continues the pipe's expansion rate, i.e. if its CSA doubles every 20", then ideally the mouth/ceiling gap would be 20" or multiples of 20". Any nearer and you theoretically get some 'floor' mass loading, ergo with a greater gap there's reduced loading, like when rapidly flaring a vent.

For other locations, the vent rule-of-thumb (ROT) of at least 3x the mouth's (effective) radius is sufficient. If it sounds too 'boomy' due to being too close, you can always scallop out the mouth like T.C. did on his recent floor loading model to relieve the pressure.

GM

[GM]

Originally posted by McFaBs
I see, I do a different calc.

I think it works like this if I've not misunderstood GM and Scott suggestions.

Considering marble and granite...........

Greets!

Maybe I drew it out and/or did the math wrong, but I approached it from an expansion rate POV like any other horn folding. A 3D CAD program construction will 'tell the tale', but I don't have either the software or skills to confirm it.

WRT using a rigid/massive base, this is the last thing you want supporting it since it will cause strong reflections back to the driver/throat, requiring what I consider excessive stuffing/damping in the pipe. Really, the bottom should in theory be made of a relatively lossy material since the floor will be plenty rigid enough even if it's a 'floater' (suspended), and if wall loaded, then the back should be also. From this it follows that if corner loaded, then the bottom and the two corner sides should be lossy to damp down unwanted harmonic energy.

GM

[Scottmoose]

I wasn't suggesting the base itself should be granite guys -sorry for causing any confusion. I'm completely with Greg on that one. That's why we put the 1in or better layer of damping on the base -to kill reflections back up the line.

The granite etc. was a suggestion for a plinth to stand the cabinet on if your floor happens to be a pain. In my case, floors are suspended (ha! it's chipboard over beams!) and it vibrates something chronic unless drastic measures are taken. A massy stone plinth is the best way I know of, unless you fancy building a couple of sandboxes. I tried out a few different coupling methods from cabinet to plinth a while back, and finally settled upon 3 semi-spherical cork feet I bought from the local independent DIY store: very effective. Not sure exactly what they're originally intended for, but this is a very good use. Blu-Tak or similar applied in sheets to the cabinet base, then stuck down is also pretty good.

[GM]

Greets!

For either 'trampoline' (really 'springy' suspension) or rigid (concrete slab or similar) floors, I recommend viscuous damped springs for the former and small mechanical business/manufacturing machine iso-feet or similar for the latter.

FWIW, since iso-feet can cost more than the speakers, an effective 'el cheapo' solution is a regular bike tire innertube for lighter speakers and trailer tire size for bigger/heavier ones formed into an appropriate size open top base, then use a hand pump to inflate it as required.

Unfortunately, the only really cheap option for 'trampoline' floors I know of is to suspend the speakers from the ceiling with rope. Making macramé speaker, TT, etc., hangers was popular around here back in the 'bad old days' of minimal/~non-existant building codes.

GM