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Old 22nd August 2008, 06:51 AM   #1
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Default Fr125s Bib

Greetings all,

I plan on building the BIB cabinets for the FR125S.

I have downloaded the BIB calculator worksheet from Zilla Audio. The pre-calculated external dimensions given are width 9 inches, depth 12 inches, height 49 inches.

I just want to be sure that I have not missed something as most BIB designs I have seen appear to be quite tall.

The example below is of someone who has built a FR125S BIB and it looks to be around 6 foot tall.
FR125S BIB Project

The dimensions on the BIB calculator are around 4 foot tall.

Have I missed something in terms of understanding the design? I would prefer to maximise bass from these little drivers where possible. Should I build the BIB cabinet for the FR125S as per the BIB calculator or is there some advantage gained by lengthening the line that I do not understand?

Thanks,

Cangaceiro
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Old 22nd August 2008, 10:06 AM   #2
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You can tune it lower at the risk of pushing the driver over-hard on material with major LF transient swings.
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Old 22nd August 2008, 01:08 PM   #3
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If I understand you correctly, if I input the drivers T/S parameters incl an Fs (70Hz) this will give me a default line length where:

Line length = speed of sound / Fs / 2

So if I set a lower Fs, then I will end up with a longer line (taller cabinet) and lower LF gain, but this is dangerous for the driver and you therefore recommend against this for both tuneability and safety of the driver?

Thanks for your reply ScottMoose. I'm just trying to understand your response more clearly as my knowledge of this subject if very small.
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Old 22nd August 2008, 01:33 PM   #4
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Quote:
If I understand you correctly, if I input the drivers T/S parameters incl an Fs (70Hz) this will give me a default line length where:

Line length = speed of sound / Fs / 2
Right.

Quote:
So if I set a lower Fs, then I will end up with a longer line (taller cabinet) and lower LF gain, but this is dangerous for the driver and you therefore recommend against this for both tuneability and safety of the driver?
You'll end up with a longer line, a lower tuning frequency and a little less LF gain; these things are relative however. The FR125SR has a lot of excursion, so within reason, you can just keep plugging in a lower Fs value for a longer, lower tuned horn. That's not dangerous for the driver per se. However, there are limits, & with that soft suspension, you could bottom it out at high SPLs on material with a lot of large LF transient swings. So the message is, if you tune low (frankly, WRT the FR125, I'd just stuff it into Terry's original cabinet & enjoy), & crank the volume up, keep an eye on the driver & if it bottoms out, back things off a trifle.
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Old 22nd August 2008, 05:22 PM   #5
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Sorry in advance if I have missed this info.

How do you work out the height of the centre for the driver hole? I haven't seen this dimension mentioned anywhere.

John
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Old 22nd August 2008, 08:02 PM   #6
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Quote:
Originally posted by john blackburn
Sorry in advance if I have missed this info.

How do you work out the height of the centre for the driver hole? I haven't seen this dimension mentioned anywhere.

John
As I recall it's sm.

That's what I've used.

for a sort of split screen or multimedia view of the BIB, there is this:
http://www.zillaspeak.com/bib-howtobuild.asp

If you select the BIB 166 it gives multiple representations
quite attractively for BIB theory.

Regards line length, I too have wondered how extreme it can be.

Right now I'm gluing up a small BIB with the measures for a 50 cent Pioneer driver (I guess they were about 10 bucks before closeout.)

This one will be a little less than 3 ft when done.

I also have a 50 center in a BIB cab for the FE127e. Even though
the low end seems less refined in this combination, I have been very satisfied with certin music sources WRT instrumentation.

The experiment is to see if the BIB made to the correct scale from the calculator retains those interesting properties.

Then I will start on some driver mods.


Lon (still looking for the definitive Enable how to.)

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Old 22nd August 2008, 08:05 PM   #7
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Wait--

zdriver is the center for your driver hole.

Sorry for any confusion. You didn't build one between these posts did you?

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Old 22nd August 2008, 09:03 PM   #8
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So = cross sectional area of the sealed end of the horn (for a BIB, this is 0, as it comes to a point & has no surface area.)

Sl or Sm = cross sectional area of the terminus of the horn

Zdriver = distance of the centre of the driver from So.

Zdriver for the BIB = 0.217L where L = total horn length.
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Old 22nd August 2008, 10:10 PM   #9
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Quote:
Zdriver for the BIB = 0.217L where L = total horn length
Cheers Chaps, that clears things up nicely.

John
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Old 22nd August 2008, 10:32 PM   #10
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I'm going through this whole experiment right now in a thread a couple of pages back (update soon). I made an oversized pair of BIB inspired pipe/horn boxes and am working my way through drivers to learn about what was happening.

The BIB calculator shows that the fr125 will work fine, but I tested the boxes with fostex 108e sigma and 126e first. I thought that making the csa a bit bigger might be beneficial, but according to my experimentation so far, the calculator seems a very safe bet to follow, as neither of the drivers I have so far seem to be a good match. (External dims IIRC - 52x8.25x14.25, very close to yours)

The 108, with it's high fs (probably even higher than published specs would indicate) had a rough time in those boxes, in exactly the same way that they would have a rough time in a ported box tuned too low for them. The 126 was not quite so bad, but severely limited in displacement unless used with a sub. The FR125 is the ticket, I just have to bite the bullet and spend some more cash.
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