Crossover DCR issue - 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 25th November 2009, 09:07 AM   #1
zaffle is offline zaffle  United Kingdom
diyAudio Member
 
Join Date: Nov 2009
Default Crossover DCR issue

Hi,

I have recently finished building a 3 way sealed box Hi Fi speaker, It sounds great.

Acoustically it measures ok,
Impedance measurements are ok (min 3.8 ohms).
Crossover is 2nd order throughout @ 480Hz and 4.2Khz
Box volume is 120 Litres
2 x 6.5 inch LF drivers (8 ohms each wired in parallel)
1 x 4" MF driver (8 Ohms)
1 x 3.4" HF driver (8 Ohms)

However when I try to take a DC Resistance reading the digital multimeter won't settle on a value. It ranges from 1 Ohm to 7 Ohms up and then back down again and carries on in this manner. Normally I would expect it to read around 4 ohms and does so on all other speakers with roughly the same impedance. Any ideas?

For the record I am aware of the difference between Impedance and DCR but I have never come across this one before. Any ideas why?

Thanks
  Reply With Quote
Old 25th November 2009, 10:05 AM   #2
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
maybe you could post the crossover topology... it sounds like you are getting some sort of effect from the caps in the crossover charging/discharging perhaps....

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 25th November 2009, 01:37 PM   #3
diyAudio Member
 
Join Date: Oct 2009
Location: new england
Most DMM's take their DCR reading @ 1Khz.
Have you tried feeding a 1 kHz signal to the speaker to hear how it responds and also hook up your DMM on ACV to see what it's doing.
  Reply With Quote
Old 25th November 2009, 01:43 PM   #4
diyAudio Member
 
zigzagflux's Avatar
 
Join Date: Oct 2006
Location: Charlotte, NC
Quote:
Originally Posted by skeptic43 View Post
Most DMM's take their DCR reading @ 1Khz.
Well, that would be a problem with the meter design. Measuring impedance at any frequency other than 0 would not give you DCR. As far as I know, every DMM measures resistance with DC.

Sounds to me like the problem is the autorange function of the meter, if it has one. Flukes are famous for bouncing around in their reading until you force the meter to manual range mode. If your meter is not autoranging, then you may have to use a battery with a current limiting resistor to force a DC current through the coil, and measure DC millivolt drop across the coil to get a good resistance meaasurement.
  Reply With Quote
Old 25th November 2009, 01:46 PM   #5
zaffle is offline zaffle  United Kingdom
diyAudio Member
 
Join Date: Nov 2009
Thanks Tony,

Schematic attached ( I hope!!)

Regards,

Zaff
Attached Images
File Type: jpg Crossover 1A copy.jpg (54.4 KB, 35 views)
  Reply With Quote
Old 25th November 2009, 02:06 PM   #6
gedlee is offline gedlee  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Novi, Michigan
This is quite common. Remember that the speaker is a microphone. WHen you measure DCR then you are only seeing the woofer. Now if there is any source of noise or vibration in the room, then the woofer will pick this up and feed it back into the DMM as a voltage. Depending on the internal impedance of he DMM this can cause very large swings in an impedance measurement. A cheap DMM will NOT reject this signal, while a better one will. A DMM is not a good way to measure DCR for this very reason.
  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
crossover issue ernestnapoleon Multi-Way 0 16th September 2007 07:48 AM
crossover issue in first 3 way mp006ltk Multi-Way 1 2nd April 2007 05:32 PM
Can you hear the crossover point of a speaker with a well-designed crossover? 454Casull Multi-Way 11 2nd April 2004 05:48 AM


New To Site? Need Help?

All times are GMT. The time now is 03:23 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