Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 498 - diyAudio
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Old 14th March 2012, 03:57 AM   #4971
GM is offline GM  United States
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FYI, example calculation: Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks?

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Old 14th March 2012, 05:48 AM   #4972
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Ok, thx for the link.

wanna see if i understand what im looking at.

its the specs of the bib
Vb is box volume
L is lenght of the line
Sm is surface area of the mouth

i guess the position of the driver along the line and dimensions of the line are given by formulae set up in the sheets.

I also gather its a result of the specs vas qts and fs.
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Old 14th March 2012, 01:29 PM   #4973
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Old 14th March 2012, 03:38 PM   #4974
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Quote:
Originally Posted by Etocynned View Post
Ok, thx for the link.
You're welcome!

Vb = 20*Vas*Qts^1.25

Again, the driver location can be varied somewhat from its L*0.217 down to around L*0.434 according to Scott [by way of MJK?].

Vas can be in liters, ft^3, etc.; just be sure to use the appropriate speed of sound [SoS] in ft, m, etc. to get the right path-length [L]. The SoS varies depending on the program used, with ~344 m/sec being the average.

Regardless, the difference from low to high in a such a long pipe isn't obviously audible plus getting decent floor or ceiling loading is much more important, so the Fs/2 tuning is somewhat flexible unless the desired ĎLí is longer than the driverís theoretical low corner frequency [Fl = Fs*Qts/2]. Even then it may not matter, but havenít experimented with, or read of any research done, though Prof. Leachís horn math implies we must rethink how the driver must be loaded.

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Old 15th March 2012, 01:53 AM   #4975
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So made a sheet for myself, hooray. Seems to work quite well, based on the equations seen in the linked post.

how does f3 relate to tuning?

i made a row to calculate fl but seems too low to be f3.

WAY TO GO! NOW IM GONNA BE LOOKING UP EVERY DRIVER ON EARTH FOR LIKE EVER!!!
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Old 15th March 2012, 03:26 AM   #4976
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'Sunk the hook' in another one, did we? Have you seen this? http://www.quarter-wave.com/General/...BIB_Design.pdf

F3 is just the half power point of the resonant system. Fl and its reciprocal, Fh, define the driver's impedance/loading BW where Fs is the mean.

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Old 15th March 2012, 03:36 AM   #4977
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You know? I read that paper a couple months ago found it intriguing but forgot about it because i didnt know what it meant.

Is he talking about how to refine sims by quantifying non coincident drive/terminus points?

If so how would they be added to a sheet? What equation would be relevant?
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Old 16th March 2012, 03:03 AM   #4978
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TBH, I don't recall the details, I'll have to read it again as time permits or you can ask him on his yahoo forum. Driver/terminus location's 'time of flight' to the listening position [LP] can definitely have a big impact on perceived performance though.

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Old 16th March 2012, 09:46 PM   #4979
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A couple of quick questions before I start ordering components for my BiB build:

1) I intend to get a set of Fostex ~6.5" drivers from Dave at Planet 10 Hifi, pre-modified. I had the FE166En in mind, but apparently he still has a few FE167E in stock, which would be slightly cheaper. Does anyone have a suggestion as to whether one would perform better than the other in this enclosure?

2) Despite going over the entire thread, I haven't found a definitive answer to what an optimal ceiling-to-mouth distance would be. The stock specs for the 166En make this distance 31" for my eight foot ceiling. By adjusting the Fs in the spreadsheets, I can bring this to about 25", without raising the speaker too high for my listening position. Would these perform at nearly the same level, or would somewhere within the range be "optimal", by theory?

Thanks in advance, everyone!
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Old 16th March 2012, 11:06 PM   #4980
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Dobbykins,

I made a BIB for a friend with the FE166EN and it worked very nicely; no experience with FE167E though, maybe others can comment. The ceiling is at 9' at my place, and IIRC the BIB with FE166EN is 64.5" tall - had no problems with them - but please note, you need to place them near corners for good bass output. I had them at my place for some time, and must say, they were very pleasing to listen.
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