Problem with BIB-165K sim

zek · 16th December 2007, 09:04 PM

I'm working on BIB Fostex FF165K sim, but I have some problems, or missuderstanding.
When I put T/S data into BIB_166_GM_v2 sheat , I get L=168,31 in. and Sm=93.50 sq.in. (more that on Zilla site - Sm=88.125 sq.in.)
If I shorten L and change Fr to 50Hz, then Sm become bigger (Sm=116.87 sq.in.)
What I'm doing wrong?
How to calculate shorter pipe?
I think that Sm must be the same - not bigger if pipe L shorten?

zek · 16th December 2007, 09:07 PM

..and the shortened one...

Scottmoose · 16th December 2007, 09:16 PM

You're doing nothing wrong. As noted elsewhere, most of the Zilla dimensions pre-date the math used in the spreadsheet by many months, and are obsolescent, if not obsolete. They'll work OK; the dimensions provided by the spreadsheets will work better however.

GM · 16th December 2007, 09:19 PM

Greets!

It takes 'x' amount of net volume (Vb) per Hz of gain BW and when you shorten it you're reducing Vb, so the wall angle and base area must increase to offset the loss in pipe loading. IOW no matter what Fp you choose, the net Vb stays the same whether tall and narrow or short and wide, though there's a point at both extremes where the simple math returns an unacceptably performing alignment.

GM

zek · 16th December 2007, 09:42 PM

Thank you Scott and GM for yours answers.
Will you be so kind to do frequency sim for my shorten pipe, because I have some trouble with MJK work sheet.
Thanks in advance.

GM · 17th December 2007, 05:20 AM

You're welcome! With its high Vas, low Qts, it needs a matching impedance amp to 'sing':

GM

zek · 17th December 2007, 09:23 AM

Hi Greg,
I'm realy surprised with the graph you attached, because it is so different to the graph on Zilla site.
It seems that this driver is not a good candidate for BIB enclosure.

GM · 17th December 2007, 02:22 PM

Greets!

I was too and frankly knew that I'd screwed up, but due to a variety of factors beyond my control at the time I couldn't find it, so posted it anyway figuring Scott would review/correct as required since he gets up in an earlier time zone, but he didn't.

Anyway, I found my multiple inputting errors:

GM

zek · 17th December 2007, 02:42 PM

Thanks Greg.

Godzilla · 17th December 2007, 02:46 PM

The 169" Line is very close to the new math with Sm of 93 compared to 88 sq/inch. Regardless of the measurements the 165k is a very fine sounding driver in a BIB.

16th December 2007, 09:19 PM	#4
GM diyAudio Member Join Date: Jun 2003 Location: Chamblee, Ga.	Greets! It takes 'x' amount of net volume (Vb) per Hz of gain BW and when you shorten it you're reducing Vb, so the wall angle and base area must increase to offset the loss in pipe loading. IOW no matter what Fp you choose, the net Vb stays the same whether tall and narrow or short and wide, though there's a point at both extremes where the simple math returns an unacceptably performing alignment. GM __________________ Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

17th December 2007, 02:46 PM	#10
Godzilla diyAudio Member Join Date: Nov 2005 Location: New York	The 169" Line is very close to the new math with Sm of 93 compared to 88 sq/inch. Regardless of the measurements the 165k is a very fine sounding driver in a BIB. __________________ www.zillaaudio.com/bib/bib.asp www.ZillaAudio.com

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16th December 2007, 09:16 PM	#3
Scottmoose diyAudio Member Join Date: Mar 2005 Location: UK	You're doing nothing wrong. As noted elsewhere, most of the Zilla dimensions pre-date the math used in the spreadsheet by many months, and are obsolescent, if not obsolete. They'll work OK; the dimensions provided by the spreadsheets will work better however.

16th December 2007, 09:42 PM	#5
zek diyAudio Member Join Date: Aug 2003 Location: Belgrade, Serbia	Thank you Scott and GM for yours answers. Will you be so kind to do frequency sim for my shorten pipe, because I have some trouble with MJK work sheet. Thanks in advance.

17th December 2007, 02:42 PM	#9
zek diyAudio Member Join Date: Aug 2003 Location: Belgrade, Serbia	Thanks Greg.

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