Crazy Impedance Curve - 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 20th August 2012, 06:42 PM   #1
abpea is offline abpea  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Central Illinois
Default Crazy Impedance Curve

I'm modeling an Alpair 6.2P driver in a closed box. When I pull up the impedance curve I get the graph below. Does it cause a problem when the impedance goes straight through the roof??
Attached Images
File Type: jpg alpair_6P_Impedance_Curve.jpg (146.8 KB, 183 views)
  Reply With Quote
Old 20th August 2012, 08:02 PM   #2
Davey is offline Davey  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Bremerton, WA.
Most likely you have the wrong information for Le in your driver parameters.

I was looking at the data sheet for that driver and it shows Le of 6.94 microhenries. If I plot an impedance file of a driver with Le of 6.94 millihenries it shows me something nearly identical to yours.

Hope that helps.

Dave.
  Reply With Quote
Old 20th August 2012, 08:25 PM   #3
abpea is offline abpea  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Central Illinois
Davey,

Good catch, thank you sir! You are correct, the difference between micro and milli is significant. See corrected graph below (looks much better now!).

Next time I'll do a better job of keeping my units straight!!

Thank you again for pointing my error out to me, much appreciated my friend!

bp
Attached Images
File Type: jpg Corrected_Alpair6P_Impedance.jpg (160.2 KB, 164 views)
  Reply With Quote
Old 20th August 2012, 09:30 PM   #4
diyAudio Member
 
Bob Brines's Avatar
 
Join Date: Jan 2003
Location: Hot Spring Village AR
OK, but that 6.94μH is at DC, correct? Anydriver will have a rising Le with rising frequency. A plot that levels out a the DC Le at high frequency is also very wrong.

Bob
  Reply With Quote
Old 20th August 2012, 09:49 PM   #5
diyAudio Member
 
DBMandrake's Avatar
 
Join Date: Nov 2010
Location: Glasgow, UK
Quote:
Originally Posted by Bob Brines View Post
OK, but that 6.94μH is at DC, correct? Anydriver will have a rising Le with rising frequency. A plot that levels out a the DC Le at high frequency is also very wrong.
Quite true. Modelling a drivers impedance curve based on Re and Le is an exercise in futility, as the Le is not constant with frequency.

The only way to do it accurately is actually measure the impedance curve of the driver, which is not difficult if you have one already.
__________________
- Simon
  Reply With Quote
Old 20th August 2012, 10:08 PM   #6
Davey is offline Davey  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Bremerton, WA.
Yeah, I have my doubts about the listed value of 6.94uH on the driver data sheet. In fact, if you look at the impedance graph on the data sheet it does show the curve rising above 500Hz. You are correct that a proper measurement of an actual driver should be made to confirm.

Anyways, the gross error at higher frequencies in his simulation that bp was seeing was certainly just a pilot error on data input.
Which, I think, is all he was really asking about.

Cheers,

Dave.

Last edited by Davey; 20th August 2012 at 10:36 PM.
  Reply With Quote
Old 20th August 2012, 10:15 PM   #7
badman is offline badman  United States
diyAudio Member
 
badman's Avatar
 
Join Date: Sep 2003
Location: Sunny Tustin, SoCal
Quote:
Originally Posted by DBMandrake View Post
Quite true. Modelling a drivers impedance curve based on Re and Le is an exercise in futility, as the Le is not constant with frequency.

The only way to do it accurately is actually measure the impedance curve of the driver, which is not difficult if you have one already.
Indeedy- I tend to look at the Le at a couple points on the rising portion of the curve, and select a value based upon the averaging of Re + Le that most closely matches the curve. Given that most of the increasing inductance in all but fullrange drivers (which is of course what we're discussing here) is above the passband anyway, this tends to make a good approximation for lightweight modeling purposes.
__________________
I write for www.enjoythemusic.com in the DIY section. You may find yourself getting a preview of a project in-progress. Be warned!
  Reply With Quote
Old 20th August 2012, 11:35 PM   #8
diyAudio Member
 
Bob Brines's Avatar
 
Join Date: Jan 2003
Location: Hot Spring Village AR
Quote:
Originally Posted by Bob Brines View Post
OK, but that 6.94μH is at DC, correct? Anydriver will have a rising Le with rising frequency. A plot that levels out a the DC Le at high frequency is also very wrong.

Bob
First a minor correction to what I said: I meant Re not DC Le.

Second, and not particularly relevant here, you need to use the Le at the cross-over frequency if you want to try textbook XO's.

Bob
  Reply With Quote
Old 21st August 2012, 08:50 AM   #9
ODougbo is offline ODougbo  United States
diyAudio Member
 
Join Date: Aug 2011
Location: Maryland USA
Is there any disadvantage using a generator - load resistor - volt meter vs. "software" to measure impedance curve(s)?

Last edited by ODougbo; 21st August 2012 at 09:15 AM.
  Reply With Quote
Old 21st August 2012, 09:18 AM   #10
diyAudio Member
 
DBMandrake's Avatar
 
Join Date: Nov 2010
Location: Glasgow, UK
Yep, it's extremely time consuming to do accurately

Also most multimeters other than high end ones have a limited frequency response and will be inaccurate above a few hundred Hz.

If you have a PC with a sound card and a couple of resistors that's all you need along with some free software to do it the easy way...
__________________
- Simon

Last edited by DBMandrake; 21st August 2012 at 09:21 AM.
  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
MLTL impedance curve..any help? mondogenerator Full Range 1 23rd October 2009 06:05 PM
Impedance Curve jwatts Car Audio 2 2nd December 2004 08:33 AM
Impedance Curve jwatts Multi-Way 4 22nd November 2004 05:45 PM
Impedance curve...... rabbitz Multi-Way 6 4th September 2003 02:52 PM
Impedance curve masterp2 Multi-Way 8 3rd March 2002 12:34 PM


New To Site? Need Help?

All times are GMT. The time now is 04:25 AM.


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