Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 418 - diyAudio
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Old 11th July 2008, 12:29 AM   #4171
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Location: New York
Will pointing the subs towards each other present any problems? Otherwise, great idea. Will you attach them directly to the BIBs or make freestanding cabinets that stand right next too them? Also, will you have one or two subs... in your small room maybe one will be enough?
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Old 11th July 2008, 03:27 AM   #4172
sedge1 is offline sedge1  New Zealand
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Hi,

No, the BIBs are 1.7m in from the corners, I'll fire the subs outwards.

Yes, I'm going to attach the subs directly to the existing cabs, they will be well braced. Separate cabs ? I couldn't bring myself to tiptoe a very thin, very tall box of impending doom in the lounge with a five year old running round.

I've had two subs for years, run active/stereo, never sounded right with one. Small room, yes, I just don't turn them up that loud (mostly)

I'll post some photos when I get the things together.

<insert evil cackle here>

Sedge.
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Old 18th July 2008, 06:10 PM   #4173
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Default some tweakage is needed

I have a BIB abd it's step brother with the double front baffle.

Interior treatment is similar but not identical.

The BIB original is giving a better midrange whereas the
double front baffle (one cutout 4 in, the interior cutout 5 in)
gives the mids coming out the front a muted effect.

So suprabaffle on these.

I do not think minor surgery such as chamfering the inside baffle
would change this.

The original 'good sounding' BIB currently has the thin wire
tweak on it but here again I think this is minor.

Both use FE127e. Both are about the same same size and the
newer sibling is closer to the calculator measures.

What concerns me is what's coming out the front and less so
what is coming out the top.

Anyway, the BIB thread lives!

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Old 18th July 2008, 07:28 PM   #4174
Variac is online now Variac  United States
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Tomorrow some friends and I are making 10 PAIRS of BOFU BIBs for the participants. We call is Speakermaking Summer Camp. We hope to make them all in a day..

Many participants are younger, so I feel we a re doing a public service getting some great sounding speakers into the world..


Mark
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Old 18th July 2008, 08:02 PM   #4175
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>>> Tomorrow some friends and I are making 10 PAIRS of BOFU BIBs for the participants. We call is Speakermaking Summer Camp. We hope to make them all in a day..

>>> Many participants are younger, so I feel we a re doing a public service getting some great sounding speakers into the world..

I am sorry to have to miss this. Very cool indeed! If you take pictures please forward them to me.

Thanks,
Godzilla

godzilla3@hotmail.com
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Old 18th July 2008, 08:59 PM   #4176
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"The BIB original is giving a better midrange whereas the
double front baffle (one cutout 4 in, the interior cutout 5 in)
gives the mids coming out the front a muted effect.

...........................Both use FE127e."



Have you tried switching drivers from one cab to the other ?

Also, don't discount small changes such as wire , sometimes it makes a BIG difference.



..........................Blake
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Old 18th July 2008, 11:41 PM   #4177
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Lon, I know you mentioned that the two cabs are roughly similar, but I'd suspect the stuffing / felt / foam, since it's easy to over-damp. Just a thought!
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Old 19th July 2008, 01:33 AM   #4178
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I hear your suggestions but what I don't understand about the
stuffing materials is how that would diminish the mid tone coming out the front.

For instance: clarinette solo is forward on the one and lost in the
tympany on the other-- or something similar.

The Lost In Translation BIB with the double baffle front has thin
foam behind the driver, fiberfill in the peak and egg crate foam on the bottom.

The Original has fiberfill in the peak, billiard felt behind the driver and
layered fiberfill (very loose) about a 1/2 inch on the bottom.

The cabinet material differs on the sides: butrcherblock glue up pune (prefabe shelving) on the Original, less than void free plywood
on the troublesome one.

To be honest, I tore down one non-BIB build and reused the plywood just so I could see what a couple of BIBs sounded like together.

Considering my usual asymmetric listening style, 2 bibs at close range may just not be a good fit.

Next round of building is an MLTL. The plywood BIB I may set up as part of a different rig in a testing/build room.
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Old 21st July 2008, 03:37 AM   #4179
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Default BiB Spreadsheet / Calculator Gotcha

I love the BiB spreadsheet. However, there is one gotcha that I noticed tonight in assembling my FE166E BiB's.

In attempting to get the a-b-c lined up correctly, I ran into trouble -- the divider was too long. In OpenOffice, I checked the formula calculating the slant (divider's) length. My driver happens to be in column F, and the slant length is calculated in cell F41:

=(IF(F21=0;"";MROUND(SQRT(SUMSQ(F30-(F13))+(F13));0.25)))

So the formula states:

If F21 (material thickness) is zero, return an empty string (nothing) to avoid dividing by zero.

But otherwise, calculate the length of the divider according to the Pythagorean theorum (hypotenuse = sum of the squares of the other sides in a right triangle).

To do that:

1. Take height (F30) minus the a-b-c value as one of the sides. Let's call this "a".
2. Take a-b-c- value (F13) as the base, and let's call this "b".
3. The slant's length (call it "c") is equal to the square root of (a^2 + b^2).
4. Round the result to the quarter inch.

The slight issue I noticed is that item #1 fails to account for the .75" of the base. The base is mounted "inside" the other four boards. So really, .75 needs to be subtracted from external height.

If not, then when you are gluing up, you'll notice there's no way to get your a-b-c to come out right. However, the fix is simple: just nudge the divider up until you get your a-b-c (north of the mouth), then trim off that excess.

So I'd recommend changing the above formula to:

=(IF(F21=0;"";MROUND(SQRT(SUMSQ(F30-F21-F13)+(F13));0.25)))

Empirically, when I nudged the divider "higher" than the mouth, until a-b-c- worked out, I got 61" and that's what the revised formula yields as well.

Anyway, thank you to all who worked on the BiB calculator -- it's terrific!
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Old 21st July 2008, 04:34 AM   #4180
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One last thought:

Technically, the base of the triangle (of which the slant is the hypotenuse) is not the value of a-b-c, but rather, the value of a-b-c minus 1/2 of the slant's thickness (material thickness, F21).

This is because the a-b-c "pinpoint" is located at the center of the divider's bottom (at the mid-point of the divider's thickness). But the slant is the hypotenuse of a triangle with a very slightly smaller base (smaller by one half of the slant's thickness).

So we could say subtracting half the slant's thickness is more accurate:

=(IF(F21=0;"";MROUND(SQRT(SUMSQ(F30-F21-F21/2-F13)+(F13));0.25)))

But it's not, because of rounding. For the FE166E, it becomes 60.5 whereas empirically, 61" is more like it. This is because the formulas are ultimately doing multiple roundings, i.e., using a rounded value to derive another value, which is then rounded.

Anyway, I really do love the BiB calculator -- it's a great time saver and a huge help for those of us who can't measure and cut too well. Thank you again to all those folks who have worked on it, directly or indirectly!
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