BIB impedance? - diyAudio
Go Back   Home > Forums > Loudspeakers > Full Range

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th November 2007, 07:37 PM   #1
diyAudio Member
 
Join Date: Dec 2005
Location: Bologna
Default BIB impedance?

Hello,

anyone have a graph of the impedance of the Fostex FF225K driver in the BIB cabinet raccomended on zillaspeak site?

thak you
  Reply With Quote
Old 13th November 2007, 11:44 AM   #2
freddi is offline freddi  United States
diyAudio Member
 
freddi's Avatar
 
Join Date: Aug 2005
here's a simulation of Z in half-space using AJ-Horn plus a comparison of that BIB vs the same volume but shorter (2.5M) concial horn to illustrate the tradeoffs. I think measured impedance may be off from predictions. I use half-space so frequency response can be checked with outdoor measurements to see how close a model might come.

note keeping the pipehorns volume fixed, the shorter horn has the upper bass advantage and vice versa with the longer horn. RCA-Fan (Bill Woods of AH!) ditched a larger/longer horn in favor of the 2.5M as the shorter horn was more accurate with cello.

power input for sine has dropped to less than 1/10 of a watt on the BIB to reach 0.3mm xmax (we don't know the 70% BL figure - any guesses?)

FF225K Z prediction
http://img220.imageshack.us/img220/3...25kbib1jw8.gif

FF225K BIB vs concial like RCA-Fan's k-slot blh
http://img218.imageshack.us/img218/7...vskslotsq7.gif
  Reply With Quote
Old 13th November 2007, 12:59 PM   #3
diyAudio Member
 
Join Date: Dec 2005
Location: Bologna
meanwhile I tried to simulate with lspcad demo:
http://img440.imageshack.us/img440/8...5khrbibvk9.png

looks very different. Did I set somethin wrong?

I want to know the impedance to make the crossover.
  Reply With Quote
Old 13th November 2007, 02:06 PM   #4
freddi is offline freddi  United States
diyAudio Member
 
freddi's Avatar
 
Join Date: Aug 2005
at high frequencies the pipe's impedance effects will drop out and you'll just have the same Z as an unmounted driver so can use the published inpedance graph in Fostex's FFl225K literature. Voice coil nductance is very low and there's not much rise even at 10Khz. You could do a tweeter crossover by "ear". typical highpass capacitor values with an 8 ohm tweeter might be 0.68uF ->1uF.

at low frequencies a passive crossover to subwoofer could be tricky due to impedance interaction effects and parts expensive.

AJ-Horn and MJK's Mathcad sheets will work for tapered pipes - - I don't know LspCAD
  Reply With Quote
Old 13th November 2007, 02:14 PM   #5
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
Greets!

Neither LspCad or any of the other standard box programs can sim a BIB nor can they predict the impedance without an inductance value (Le), so you're left with the factory's published plot to approximately calculate it:

Le(mH) = [(Zxo^2-DCR^2)^0.5/(2*pi*Fxo)]*1000

Where:

Fxo = some frequency point away from Fs
Zxo = impedance at Fxo
Dcr = Re

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote
Old 13th November 2007, 04:26 PM   #6
diyAudio Member
 
Join Date: Dec 2005
Location: Bologna
I also found this to calculate the LE

http://img444.imageshack.us/img444/8250/ff225klesu1.png

So I use the impedance on the fostex graph to cross the tweeter.
  Reply With Quote
Old 13th November 2007, 05:32 PM   #7
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
Greets!

Since I get 0.226 mH using the formulas I posted, I don't recommend using this on-line calculator without multiplying its 'Henry' results by 1000 to get the labeled mH. Indeed, if you can, email them and ask them to review/correct it.

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote
Old 14th November 2007, 09:47 PM   #8
diyAudio Member
 
Join Date: Dec 2005
Location: Bologna
So to cross the FF225K I use the published impedance.
Obviously for FT17H I use again the published impedance since it is a tweeter.

And if later, a lot later, if I need more SPL I would like to add a woofer making a 3way I must use the impedance of AJ horn but using the LE value into simulation, right?


Now I made a sim for a cross. It's a 2nd order cross with inverted polarity on the tweeter

With diffraction sim
Click the image to open in full size.
schema
Click the image to open in full size.
without diff
Click the image to open in full size.

What do you think about?
  Reply With Quote
Old 15th November 2007, 04:24 AM   #9
GM is offline GM  United States
diyAudio Member
 
GM's Avatar
 
Join Date: Jun 2003
Location: Chamblee, Ga.
Quote:
Originally posted by testarossa2k

And if later, a lot later, if I need more SPL I would like to add a woofer making a 3way I must use the impedance of AJ horn but using the LE value into simulation, right?

What do you think about?
Well, you will need to design a parallel notch filter to flatten the F225K's Fs peak as well as designing a zobel for the woofer based on whatever 'Le' you use, whether calculated or simmed.

Looks good on paper!

GM
__________________
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What impedance? jaya000 Multi-Way 11 21st November 2008 07:04 AM
Impedance rate VS impedance stability TomatoBangBang Tubes / Valves 6 4th September 2008 10:46 PM
Hi Vi SD1.1 impedance guitarded Multi-Way 0 3rd February 2008 08:35 AM
Impedance and SPL.. TroelsM Multi-Way 5 26th September 2005 12:52 PM
Need help understanding transformer impedance ratios and impedance matching percy Tubes / Valves 5 28th February 2005 08:35 PM


New To Site? Need Help?

All times are GMT. The time now is 06:19 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2