OB MJK paper - are the XOs Butterworth? - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

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 24th September 2010, 10:38 PM   #1
NYCOne is offline NYCOne  United States
diyAudio Member
 
Join Date: Jul 2010
Blog Entries: 1
Default OB MJK paper - are the XOs Butterworth?

I read MJK's paper on OB speakers and I am going to embark on a Fostex, Eminence build. Are the crossovers Martin describes 2nd order Butterworth? He has Caps at 24 and 68uF and coils at 4 and 9 mH. I can only match these to Butterworth. Should the XOs be LR?
  Reply With Quote
Old 26th September 2010, 02:18 AM   #2
holdent is offline holdent  Canada
diyAudio Member
 
Join Date: Nov 2005
Location: Ontario
He uses a 2nd-order Linkwitz-Riley low pass filter at 200Hz and a 2nd-order Bessel filter at 500 Hz for the high-pass.
  Reply With Quote
Old 26th September 2010, 08:26 AM   #3
NYCOne is offline NYCOne  United States
diyAudio Member
 
Join Date: Jul 2010
Blog Entries: 1
I may be using the wrong calculations, but when I do a LR at 200Hz for an 8ohm driver I get very different cap and coil values than Martin's paper.

LR at 200Hz for 8 ohms - Cap=50uf Coil=12mH
Bessel at 500Hz for 8ohms - Cap=23uf Coil=4.4mH

The Bessel kind of fits the paper, but what am I doing wrong on the LR?
  Reply With Quote
Old 26th September 2010, 01:46 PM   #4
diyAudio Member
 
Join Date: Oct 2004
Impedance of the Alpha15 at 200 Hz will be around 6 ohms which also fits.
Maybe MJK could have explained his calculations a bit more.

/Erling
  Reply With Quote
Old 26th September 2010, 04:17 PM   #5
diyAudio Member
 
Join Date: Jan 2007
Martin doesn't visit forums anymore. Ask him via his Yahoo group: Quarter Wavelength Loudspeaker Design
  Reply With Quote
Old 26th September 2010, 04:58 PM   #6
NYCOne is offline NYCOne  United States
diyAudio Member
 
Join Date: Jul 2010
Blog Entries: 1
I'm new at this, it sounds like one uses the impedance at the frequency of the crossover and not the entire driver when doing crossover calculations. is this correct?
  Reply With Quote
Old 27th September 2010, 01:41 AM   #7
CLS is offline CLS  Taiwan
diyAudio Member
 
Join Date: Jun 2005
Location: Taiwan
Not only at the XO frequency, a larger picture should be taken into acount. The XO circuits and drivers are interacting full band. An ideal method is to flatten the impedance of the drivers first, then do the XO jobs. You'll need Zobels for the rising towards the high, LCR notch for the low end resonance... etc. Sometimes more (unfortunately).

In the end, electrical curve shape doesn't matter at all. What you should aim for is the acoustic results. It's just too complex to describe in one or two posts. Issues in drivers themselves, baffles (or boxes), the interactions between them... all over the place.

Doing XO design from scratch and by pen/paper/calculator/ears, you'll need a LOT of time. I'd suggest getting a tool to measure the impedance of the driver, and a mic+RTA to see what really happens in acoustics. Those are cheap and easy to get now. You'll be easier and much more successful with them.

Good luck
  Reply With Quote
Old 27th September 2010, 05:53 PM   #8
holdent is offline holdent  Canada
diyAudio Member
 
Join Date: Nov 2005
Location: Ontario
Martin only notes the xover frequencies and slopes in his paper and not what type they are. However, in the MathCad worksheet that he distributed as an example of an OB with an FE103E and Alpha 15A uses a LR filter for a low pass and Bessel for the high pass -- he did not go into to any detail about the xovers in his paper.

Martin only implements "textbook" crossovers in his worksheet and you can simulate the use of a Zobel by setting the impedence = 0. However as, CLS notes, you need to enter a considerable amount more of driver specific behaviour before being able to accurately predict how they might behave. Martin's worksheets aren't intended to be used for that.
  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
MJK OB over H-Frame finished gvimhoof Multi-Way 17 31st March 2012 09:29 PM
FS: Parts Bundle MJK Jordan OB Project $425 Michael Rothacher Swap Meet 6 16th February 2011 12:37 AM
DIY pass amp for MJK OB ecir38 Pass Labs 2 20th March 2010 04:56 AM
looking for MJK OB article for dual 15's yan6 Multi-Way 3 23rd July 2009 03:55 AM
MJK OB-bass study skorpion Multi-Way 38 5th March 2008 11:46 PM


New To Site? Need Help?

All times are GMT. The time now is 03:34 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