BIB questions

[j.michael droke]

(1) Using GM's BIB calculator spread sheet to calculate the depth, width and dimensions a,b,c, will fix these dimensions by formula. If the spread sheet formulas are revised to "plug-in" a user selected width, then calculate the depth by dividing the area "Sm" by user width and recalculating dimensions a,b,c - will this change effect the acoustic output of the BIB enclosure? This revision will not change the box height, box volume, box area, or Fb.

(2) GM states Fb will be approxmately Fs/2. (3) F3 would be expected to fall between Fs and Fb, so what F3 can we expect? (5) Is there a way to reliabiliy calculate the F3?

Gm's spread sheet is quick and easy to use, and after trying several diferent driver perameters, you can easily pick drivers to fit a box sized to your needs. Thanks to GM once again.

...regards, Michael

[rjbond3rd]

Yes, big thanks to GM! I recall that he chose the ratio of width to depth (1 to the square root of 2 or ~1.4 if I recall correctly) in order for a-b-c to be equal. However, I also recall GM saying that there is flexibility within reason.

I hope GM or Scottmoose will correct me if I've misstated that.

By the way, are you trying to make your BiB baffle wider, or skinnier?

In terms of predicting F3, you can do all that and more with Martin King's BiB worksheet which is /really/ worthwhile because it takes so many variables into account. I recommend this article because it's not only an intro to his worksheet, it's also an explanation of how and why the BiB works: General Speaker Related Articles (last article).

The beauty of the BiB, though, is that you can pretty much just crank it out and have fun. I spent too much time fussing over the details and in the end, it did "just work" at least for me, after a bit of tweaking.

One word of advice though. I've heard short BiB's (~4 feet tall) and to me, they did not exploit the corners when firing upward, and inverting them means missing out on the ceiling's lack of obstacles. I personally think that a room with 8-foot ceilings needs a BiB that is roughly 6 feet tall. I'm not sure "how tall is too tall," as I haven't tried a driver that would end up with a 7-foot BiB (maybe soon though as I did just get a driver that would require that much height).

EDIT: You might want to post your BiB questions here: Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks?

[pjanda1]

The response of the BIB is even more room dependent than most enclosures, so even if you sim it, the F3 probably means even less than usual. There was some discussion of aspect ratios during talk of the "monolith" deep in the BIB thread. I believe it was decided that one could use fairly extreme ratios without dire consequences.

The BIB is, in general, a pretty flexible design. The spreadsheet gives optimal values, but I don't believe many folks have experimented to see how greatly things change if one does not use them. Many of us that built BIB's did so prior to GM's formula, and each cabinet had its own set of priorities and tuning. Mine had a smaller Vb and lower tuning than the max-flat alignment. So, the F3 was higher, but the rolloff shallower. It worked really well in my room, and I would not have wanted more gain!

IIRC, Terry Cain himself shoehorned 6" drivers into BIB's made for 4.5"ers. Simulate the dimensions you want if you are able. If not, try and keep the Vb and length similar to the formula. Either you'll like their sound and size or you won't. The specs probably won't make or break you.

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

[Scottmoose]

The room dominates as noted above; nominal anechoic F3 doesn't really tell you much. Yes, the WxD ratio is 1:1.414

Terry's original BIB was essentially a design from the Fostex craft manuals (almost impossible to get hold of now) for the 4 1/2in FF125K of all things. As far as I can tell, he converted it to Imperial & 1in material; made a few minor tweaks, adding the suprabaffle & adjusting the internal baffle slightly to facilitate a grill across the horn mouth, and used the defunct RS40-1354. I believe he tried up to the FE166E in them with few other changes; he made a few other prototypes too of different dimensions. One was even a pre-production design he was intending to build, & showed with his single-horn BEN back in '01, but never went further, probably because Fostex chose that moment to replace the FE168Sigma he built it for.

Either way, these big old fashioned pipe-horns are inherently a very forgiving box, providing you don't do something completely daft. Greg's Vp formula yeilds the slightly underdamped alignment he (and I) generally prefer for boxes of this type, as it gives more tuning flexibility, although it also means a little more work dialing them in of course. I'm still rather fond of them; they make a very good first (large) project, and an excellent introduction to horns.

[PKNJ]

As long as we're not lost in upteen pages of BIB thread, I've got a question.

If the BIB is supposed to fill in enough low end to avoid having to use any BSC circuit, doesn't baffle width have an effect?

Shouldn't baffle width be chosen to compliment the low end reinforcement? Smart people can calculate all this stuff, is it included in the spreadsheets?

Thanks for any clarification on this.

[Scottmoose]

Along with room-gain, yes, it does. Circuits are generally unnecessary for them if properly (corner) loaded.

[pjanda1]

Originally Posted by PKNJ

If the BIB is supposed to fill in enough low end to avoid having to use any BSC circuit, doesn't baffle width have an effect?

Shouldn't baffle width be chosen to compliment the low end reinforcement? Smart people can calculate all this stuff, is it included in the spreadsheets?

I've had that thought too, but keep in mind that this isn't a precision approach to BSC. BIB's are not about perfectly flat frequency response, but they are wonderful in other ways. You do have some room to adjust the tuning. The amount of stuffing you put in the bottom should affect the bandwidth the enclosure covers, and you can certainly alter the amount of gain. In addition, the recommended corner placement tends to work against the need for BSC. So, between playing with placement and stuffing, you can get a more or less flat balance in room. If you feel like there is a gap between the baffle step and room gain, you can also add a "suprabaffle".

I think it is pedantic to worry about perfectly flat response below a couple of hundred hz anyway. The room has a very significant influence and un-flat response. If you end up with a third of an octave between the baffle step and the enclosure gain or 1/2 octave overlap, in my experience, that is pretty minor compared to the bumps and suckouts the room will be tossing your way.

The BIB loads the room in a manner than is unique in my experience. Build 'em and see. My next speaker is going to be something entirely different: a dipole that will interact with the room as little as possible. Given that ScottMoose, Dan Mason, and other early BIB advocates thought the BIBs sounded like dipole woofers despite being nearly polar opposite approaches to bass reproduction, I'm really curious to get them done. Few days go by when I don't regret leaving my BIB's in Minnesota.

Paul

[rjbond3rd]

Personally, I want to find the "ultimate" BiB driver, which for me is one that produces ~20Hz bass in-room. (I'm using two BiB's as a poor man's home theater setup.)

[Leglandu]

I confirm BIBs work fine when placed in corners; my FE168ES was able to produce a real 37 Hz (a little bit below but possibly just harmonics) with a natural flat curve and a romantic sounding, at low or middle levels.

Now, when I had to move to a "simple wall" configuration, I lost the lows. It is possible to EQ to compensate but it pushes hard the driver to do the job and the sound is not natural any more, the magic is gone

Another problem is you get lows if the BIB is right against the wall... but you'll have to draw it aside (from 20 cm or more) to get a correct imaging !?

Concerning the comparison with dipoles, yes the sound is similar, very aired and you don't "see" the enclosures.
But also a difference : the BIB activate the resonances of the room a lot more that a real dipole, and in a small squared room like mine it's too bad.

So I totally agree with pjanda1 about the response of the BIB more room dependent than most enclosures, IMHO the BIB is a nice solution in a nice rectangular room with nice corners available...

[j.michael droke]

Hi There: First, many thanks to all who responded to my first questions. You provided information and sources for further study, which has generated another questions:
(1) All of the SPL response curves show a big dip (10-12db) at approximately 100hz plus or minus 25hz. Is this effect comming from a resonance generated by the truncated volume from the driver to the dead end (pointy end)? I also noticed this effect in Hornresp simulations for TH's designs (back chamber S1 to the driver), which only goes away when the back chamber is removed.
...regards, Michael