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How important is matching DCR in mid/high compression drivers


Tizman

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Hi All.  

How important is DCR matching, the type done with an average DMM, in pairs of mid/high compression drivers?  

Pairs of compression drivers are sold online all the time that are measured this way and presented as matched for sale.  Is this sort of measurement any indication of actual matching with respect to frequency response and SPL matching?

If it is, how close do two compression drivers have to be in this DCR measurement in order to be considered matched?

Also, if the drivers are mismatched, how do you go about matching them?

Thanks in advance for your replies!

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I have seen them off by up to 5% or so.  I am not sure what the rule of thumb is but the real measure is the frequency response and impedance sweeps.  If they are more different than a small percentage and being used for stereo, I would be hesitant.  The closer they are the more likely they will be a closer match, particularly for use with a passive crossover and when you are talking about stereo imaging.  You don't want your sound stage to flop around, worse yet, not have one.

This would be a coil measurement so I don't think you can change that without changing the diaphragm.  This is why a number of high end drivers for stereo are sold in matched pairs and measured response / parms within a particular SPECIFIED tolerance. 

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6 hours ago, pzannucci said:

 

I have seen them off by up to 5% or so.

 

Thanks for the reply. I am supposed to be picking up a pair of JBL 2425J drivers tomorrow that measure 6.8 and 7.5 Ohms. These are 16 Ohm drivers, so both numbers seem a bit low, and there is a .7 Ohm difference between them. This is much more than 5%.  They are a good deal, but if I need to replace diaphragms, they won’t be.  I have this question posted on DIYAudio as well, and this was the response...

 

“DCR doesn't help except to tell you if you have an open or dead short. DCR is not useful at all in matching drivers otherwise. I think it's probably also true you could use DCR as a very rough guage of having a good or bad driver. Like, if it's 0 ohms, send it back, if it's infinite send it back. If it's 4 Ohms +- 0.5 Ohm it's probably worth more rigorous testing. 


When drivers are matched, you want the acoustic output and impedance chart. Not a lot of hobbyists do this, especially since they usually can't afford enough drivers to find pairs that match better than others. If you buy 200 drivers however, you measure each one and use a computer to find the one's that are closest. Of course, some manufacturers have tighter tolerances than others, so you may discover after measuring a few that matched pairs is too much effort. 


As a hobbyist, you buy 2 drivers, and hope for the best, but!! smile.gifWhat you can do is measure each driver and attempt to design a custom crossover for it. 



You can use something like XSim to show you how each driver would work, and compare to see if there is enough of a difference to tweak the crossover in each speaker. It sounds like this could be fun. I have read of some manufacturers claim they do this for every single speaker. “

 

 
 
 
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15 hours ago, babadono said:

I loves it. On the internet everybody is an expert:)

babadono:  There is almost no info whatsoever (that is searchable with Google) on the matching of compression drivers.  It appears that your last post is intended to be sarcastic, so do you have different information or experience with this topic?  If so, please share, as I have been unable to find anything else on the subject.  Thanks!

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18 hours ago, babadono said:

I loves it. On the internet everybody is an expert:)

Of course.  Actually a lot of good information if you can wade through it and have the appropriate background.

Thank you for your insight and contribution.

 

19 hours ago, Tizman said:

Thanks for the reply. I am supposed to be picking up a pair of JBL 2425J drivers tomorrow that measure 6.8 and 7.5 Ohms. These are 16 Ohm drivers, so both numbers seem a bit low, and there is a .7 Ohm difference between them. This is much more than 5%.  They are a good deal, but if I need to replace diaphragms, they won’t be.  I have this question posted on DIYAudio as well, and this was the response...

 


You can “DCR doesn't help except to tell you if you have an open or dead short. DCR is not useful at all in matching drivers otherwise. I think it's probably also true you could use DCR as a very rough guage of having a good or bad driver. Like, if it's 0 ohms, send it back, if it's infinite send it back. If it's 4 Ohms +- 0.5 Ohm it's probably worth more rigorous testing. 


When drivers are matched, you want the acoustic output and impedance chart. Not a lot of hobbyists do this, especially since they usually can't afford enough drivers to find pairs that match better than others. If you buy 200 drivers however, you measure each one and use a computer to find the one's that are closest. Of course, some manufacturers have tighter tolerances than others, so you may discover after measuring a few that matched pairs is too much effort. 


As a hobbyist, you buy 2 drivers, and hope for the best, but!! smile.gifWhat you can do is measure each driver and attempt to design a custom crossover for it. 



use something like XSim to show you how each driver would work, and compare to see if there is enough of a difference to tweak the crossover in each speaker. It sounds like this could be fun. I have read of some manufacturers claim they do this for every single speaker. “
 

 
 
 

Not too far off actually.

Too bad JBL doesn't give the Re or DCR specs of each driver.  Considering 8 ohm is usually in the 6.x range, I have seen the Klipsch 16ohm drivers in the 11.x range.

 

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8 hours ago, babadono said:

So R is not part of Z. All that studying and time in tech school and college for nothing. My bad.

I was not referring to anything you said or asked but to the post from DIYaudio.

Peace out.

Some sarcasm on both our parts though in general you are right.  

As you know you have to use a different type of 80/20 rule (80 bad/20 good) on the internet.  I'm hoping this forum does a little better then that hence the "wade through it" comment.

7 hours ago, Tizman said:

babadono and pzannucci:  Thanks for clarifying this for me!

Tizman, you should invest in something inexpensive like Woofer Tester or DATS and Omnimic from Parts Express if you are going to be doing some DIY.

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4 hours ago, pzannucci said:

Tizman, you should invest in something inexpensive like Woofer Tester or DATS and Omnimic from Parts Express if you are going to be doing some DIY.

This is certainly true.  That said, I am mostly a tube amp builder, and I am out of my element with speaker building.  This explains the dumb questions.  That said, I am looking at buying a pair of used CDs, that will not be returnable, and that have been measured by the vendor for DCR. They don’t measure closely, so I was hoping to get a quick answer as they are being offered for sale locally and I would like to get them quickly, before they are sold to someone else, assuming the DCR difference on its own is not a concern.  Matching DCR seems to be a selling point online, and these don’t match well...

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I personally would worry too much about the difference in the DCR in this case, or how much different it is than its rating. There are so many other variables to the end result of reproducing amplified sound. If you are doing any kind of equalizing then it is a moot point. Since you are a tube amp builder you are aware of all of the differences between channels within your amp, like capacitor tolerances, or tube output/ bias difference. My point is, If they are drivers that you want and local, I would go for it. All of the differences in tolerances in the signal chain can be compensated for in one way or another.

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4 hours ago, Deang said:

Silly stuff, seriously. 

As in silly to worry about it?  I'm a bit obsessive-compulsive, and I worry.  (For example, ODS123 has me thinking about rebuilding my La Scalas in MDF.)  Also, a pair of Altec 806-8a CDs has come up for just a bit more money locally, so now there is also competition for my hard earned money.  I think I need to drink more...

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On 1/24/2019 at 5:02 AM, Tizman said:

babadono:  There is almost no info whatsoever (that is searchable with Google) on the matching of compression drivers.  It appears that your last post is intended to be sarcastic, so do you have different information or experience with this topic?  If so, please share, as I have been unable to find anything else on the subject.  Thanks!

You just have to get them curved. Prefereably with the Xover if it's passive. I use room EQ so it swamps out any variable so it's not that critical.

 

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2 hours ago, ClaudeJ1 said:

You just have to get them curved. 

Are you referring to the JBLs or the Altecs?  The Altecs have a dropping HF tesponse, and will require a passive that helps to correct this.  There are a couple of crossovers schematics available online that will do this.  If you are referring to the JBLs, I honestly don’t have a clue how to go about correcting for this passively.  

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On 1/26/2019 at 4:20 AM, Tizman said:

Are you referring to the JBLs or the Altecs?  The Altecs have a dropping HF tesponse, and will require a passive that helps to correct this.  There are a couple of crossovers schematics available online that will do this.  If you are referring to the JBLs, I honestly don’t have a clue how to go about correcting for this passively.  

All compression drivers have a drooping HF response. The difference in impedance in the JBL that you are worried about is 10%. Worst case scenario, if that translates directly into a difference into Sonic Decibels, then you are looking at a difference in level of 0.426 DB difference. Your channel to channel amplifier balance in Stereo will be off more than this. Besides, even if your 2 channels are "perfect" I doubt you would ever hear the difference in level. Also, unless you have a perfectly SYMMETRICAL ROOM, there will be a lack of balance there. So in my opinion, you are worried about nothing that is of real consequence in the listening. IF and only IF you can ever hear a difference, you can just swap them Right to Left and be done with it.

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