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 1st February 2011, 08:50 PM   #1
Sony is offline Sony  Europe
diyAudio Member
 
Join Date: Sep 2004
Location: Europe
Default Pair of woofers with different Re's?!

I got a pair of woofers (AAD 5" aluminum) I would like to use to build a pair of 2-way monitors and I measured the DC resistance to be quite different between the two:

Re(1) = 4.6 ohm
Re(2) = 6.8 ohm

Can this sort of difference be found normal? Or will this probably mean that both the impedance curve and the nominal impedance of these drivers might be rather different?

Thanks and regards
  Reply With Quote
Old 2nd February 2011, 08:35 AM   #2
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
Hi Sony, what is the manufacturers specified re? small differences can be expected but a difference of around 30% (taking the higher one as the reference) seems extreme to me.

6.8 looks like a normal value for a nominally 8 ohm speaker. 4.6 is too high for a nominally 4 ohm speaker and much lower than I would expect for an 8 ohm. Were these purchased new? If so I'd be sending the 4.6 ohm one back if it is a nominally 8 ohm driver.

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 2nd February 2011, 10:14 AM   #3
Sony is offline Sony  Europe
diyAudio Member
 
Join Date: Sep 2004
Location: Europe
Thanks Tony.

I haven't the original specifications, these drivers are not sold.
The dealer gave me these spare pair because the original drivers were not in perfect condition (I bought the speakers as new). The original speakers are the AAD 2002 from Phil Jones.
I agree with you, they probably have different impedances and it might be on proposite... These AAD 2002 speakers have a 2.5-way configuration with two woofers like these per speaker. I now wonder if these two spare woofers may not have different impedances since the AAD 2002 are a 2.5 and not a 2-way design. Both woofers only have low-pass filters (and zobel), one at the XO point with the tweeter and other at a much lower point (about 500Hz).
So, bellow 500Hz the overall impedance is the combined impedance of both drivers (after zobel rectification). Maybe the designer chose the bass-only woofer to be of higher impedance so that the impedance curve of the speaker wouldn't drop to very low levels bellow 500Hz.

So, maybe one woofer is really 8 ohms and the other 6 ohms. Now this takes me to another question - can I still use these woofers with different impedances in my 2-way/2-drivers per speaker project? I am assuming that:
- If I use different zobel's per side I will get closer final impedances between L and R.
- If I design the crossover assimetrically L-R with the woofer's right impedances in mind, the curve will be flat on both sides.
- Eventually one speaker will take a little more current and play slightly higher, but if I attenuate the lower impedance driver by 1dB or what it takes, both sides will be equal.

Will these assumptions be correct or should I get other drivers for my project?

Note: My project is to build a high-end purest 2-way small monitor using these spares that have really amazing bass, probably like there is nothing available on the drivers market at this 5" size.
  Reply With Quote
Old 2nd February 2011, 10:42 PM   #4
diyAudio Member
 
Join Date: Apr 2010
You are building 2-ways right? TM? One woofer in the left speaker, and the other in the right, correct? Not a MTM or TMM.
  Reply With Quote
Old 3rd February 2011, 01:02 AM   #5
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
Hi Sony, if you have access to measuring equipment you could try measuring the impedance curve of both and derive their T/S parameters. You could then try adding in 2.2 ohms of series resistance on the low impedance one, and re-measure the T/S parameters. I don't know whether the series resistance will change the params or not, having never gone into the mathematics behind deriving the params, however I do know from modelling that adding series resistance before the driver DOES change the results of the model, so I suspect it will change the T/S params.

If the two speakers have similar T/S params when the series resistance has been added to the low impedance driver, then you may then be able to simply do everything else the same (making sure the series resistance is between the driver and the crossover), and hopefully you won't even need to worry about levels... I guess there is only one way to find out

For the approach you outlined to work I would think that the drivers would need to have similar T/S params when measured without any series resistance added.

Before you expend too much effort though I would try each driver running full range in a test box (playing music you are familiar with) and see if they sound the same (when levels are adjusted appropriately). The thing that concerns me is that the one with lower impedance may in fact be faulty, perhaps some shorted windings in the voice coil, if this is the case then its motor will behave differently to the other driver, and the chances you can get a decent match between channels would be I think low.

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 3rd February 2011, 10:56 AM   #6
Sony is offline Sony  Europe
diyAudio Member
 
Join Date: Sep 2004
Location: Europe
kbgl, that's right. It's a TM rear ported (compact monitor).
The woofers I'll be using are spares of a MTM 2.5 way speaker.

Tony, thanks again for such great tips.
I have no specifc measurement equipment although I have a Behringer equalizer and mic that I can use in the test you mentioned to check the response curve and levels. I have now finalized the enclosures and can use them for the test.

I am particulary concerned with the possibility you raise of having shorted windings in the voice coil. These drivers are magnetically shielded with a really heavy cover made of lead. I assume I won't be able to fix it if that's the problem.

I have spent lots of time building the enclosure and if I can't use these drivers the project will be compromissed...
  Reply With Quote
Old 3rd February 2011, 11:31 AM   #7
tinitus is offline tinitus  Europe
diyAudio Moderator
 
Join Date: Nov 2005
you can use a 4ohm and 8ohm woofer together in one channel, preferably as 2.5way

but you cannot use a 4ohm in one channel, and 8ohm in the other channel

well, you might be able to make it work for a somewhat flawed workshop speaker, but not good quality
  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
Gorlich, Micro-Precision Z130 Woofers, 5", $150 Pair, Best Woofers In The World!!! NagysAudio Swap Meet 10 20th June 2012 04:49 PM
Pair of ScanSpeak 18W8545K woofers Mcgilvrey007 Swap Meet 2 4th December 2010 02:12 AM
Eton 8-800 woofers pair gaijinmike Swap Meet 0 9th June 2010 10:30 AM
New pair Dayton RS-150S-8 woofers boywonder Swap Meet 3 4th May 2010 04:45 PM
FS or trade 1 pair Dynavox 6.5" woofers, 1 pair of Tweets.. JCoffey Swap Meet 4 20th September 2006 04:56 PM


New To Site? Need Help?

All times are GMT. The time now is 02:39 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