Deviation in DC Resistance/ Ohm, tweeter. How much is acceptable?

[MAB]

Few driver manufacturers do actually spec a tolerance on DCR but one that does, PHL Audio, usually have a +-10% spec, and from my own measurements on batches of drivers I would state you can't expect less than +-5% DCR variation from standard processes used during driver manufacture, so a +-10% spec seems to be a reasonable choice.

In your case, I thus would not loose sleep over it. At any rate, in case of doubt a comparative impedance measurement should be done to check if everything is okay.

I was thinking about this... Agreed that driver manufacturers have tolerances, like +-5% or 10%. But, I actually don't expect within a manufacturing run or even from run to run to see big differences, especially not as large as OP sees here (7%). I've measured every driver I ever used, and in my admittedly limited experience I don't see DCR mismatches as large as OP. So maybe I am a bit alarmed at this delta. To try to prevent raising a false flag, I measured a bunch of drivers I have lying around. All but one are used.

Seas W18E001 V1:

Driver	DCR (Ohm)
W18E001 V1 driver_a	6.220
W18E001 V1 driver_b	6.153
W18E001 V1 driver_c	6.069
W18E001 V1 driver_d	6.057

Seas W18E001 V2:

Driver	DCR (Ohm)
W18E001 V2 driver_a	5.865
W18E001 V2 driver_b	5.937
W18E001 V2 driver_c (new, unused)	5.912

A/D/S woofer:

Driver	DCR (Ohms)
woofer_a	3.218
woofer_b	3.246
woofer_c	3.218
woofer_d	3.294

A/D/S Tweeter:

Driver	DCR (Ohms)
tweeter_a	4.022
tweeter_b	4.224
tweeter_c	4.206
tweeter_d	4.211

Seas W18 V1 and V2 have different spec sheets, but claim the same DCR. I think quoted DCR is a vague thing of little or no meaning, so I do ignore that. V1 and V2 do have different T/S parameters, and different repsonses. And the two versions means differ by ~0.2 Ohm, but I don't see getting two samples differing by 0.4 Ohm based on random run to run, or even a manufacturing change that requires a new spec sheet. The A/D/S woofers and tweeters have been in four different cars and are over 30 years old and have coils with DCR much tighter than 0.4 Ohm. Add this to the tweeter DCR measurements, I am feeling like 0.4 Ohm is too large for a coil of wire that was allegedly precision-wound!
My thought is it is a coil of wire, the only thing that could go wrong is one tweeter was wound with wire that is 7% larger cross section than the other, or one tweeter got fewer turns on the voice coil (I hope not!). It seems this would be a pretty difference in wire tolerance...

I would consider the tweeters guilty until proven innocent, since if there is a problem it should show up in the acoustic measurements. I am eager to be proven wrong though!

 

[MAB]

REW you say.. I thought I would look into in the future, hopefully soon as I will connect my UMIK. But I might have to look over my laptop and possibly upgrade some programs. I'm lousy with data so I've been dragging my feet on getting things up and running.

Hope this helps. Yes.



Sounds reassuring. Nop, I won't lose sleep over this, I was mostly curious about how it works, with deviations between different speaker elements. What to expect and accept.

_____

In any case, I thank you all for your answers! This is interesting. Good tips and advice.

I'm happy to help with REW.
If you already have the UMIK, super. You could be up and running in a few minutes. PM me if you need offline help. Or post to this thread, other's are likely interested in the results and can help too.

 

[Verdinut]

For a driver DC resistance, we shouldn't be concerned for a variation of ±10% from the manufacturer's published values.

As for passive crossover components, a variation in values of up to 10% is acceptable and for all practical purposes inaudible IMO. As a matter of fact, I would be more worried about expensive speakers with electrolytic caps in their passive crossovers.

 

[MAB]

For a driver DC resistance, we shouldn't be concerned for a variation of ±10% from the manufacturer's published values.

As for passive crossover components, a variation in values of up to 10% is acceptable and for all practical purposes inaudible IMO.

Agreed. Manufacturers leave wiggle room, often for changes in the manufacturing process that don't lead to changes in form, fit, or function.
I think the OP is concerned that for two units, one measures 5.6 Ohm and the other measures 6.0 Ohm. The drivers were purchased used, so OP is right to be a bit paranoid. 0.4 Ohms is in fact quite a large difference in my experience, and by the data I just collected. I just measured several different groups of drivers, and the largest difference within a group is less than 0.2 Ohm. I worked as a car stereo installer years ago, I checked every driver first before I started an install so I didn't install a dud, and every driver in the car I was about to work on. Probably thousands of pairs. Same for the DIY stuff I do now. I don't expect to see manufacturing tolerances of 0.4 Ohm, more like 0.1 Ohm.

 

[DanielT]

Quick question, should I change the title of the thread to : Deviation in Ohm, tweeter. How much is acceptable?

 

[DanielT]

I'm happy to help with REW.
If you already have the UMIK, super. You could be up and running in a few minutes. PM me if you need offline help. Or post to this thread, other's are likely interested in the results and can help too.

Many thanks for the offer! I will return, definitely. Maybe this weekend. I want to get everything started then, REW, UMIK, unpack a microphone stand I bought.
I will get the stuff out.Whether we take it here or via PM, we'll see.

Regarding the differences on my drivers. I don't fully trust my cheap multimeter that I bought at a cheap nick nack store.

The drivers were purchased used, so OP is right to be a bit paranoid....There may be a risk of that, paranoia

 

[MAB]

Quick question, should I change the title of the thread to : Deviation in Ohm, tweeter. How much is acceptable?

If you want to be absolutely correct. Or "DC Resistance". Ohm is great though. He fought hard to get us modern understanding of electricity. And paid a pretty hard price for it...

 

[Verdinut]

Quick question, should I change the title of the thread to : Deviation in Ohm, tweeter. How much is acceptable?

My simple answer is if there is not more discrepancy than 10% in DC resistance or real impedance between any two same model types of driver, either tweeter, woofer etc., then you should stop worrying about the situation and enjoy your music.

 

[DanielT]

If you want to be absolutely correct. Or "DC Resistance". Ohm is great though. He fought hard to get us modern understanding of electricity. And paid a pretty hard price for it...

I took both of them, heh heh.

 

[DanielT]

My simple answer is if there is not more discrepancy than 10% in DC resistance or real impedance between any two same model types of driver, either tweeter, woofer etc., then you should stop worrying about the situation and enjoy your music.

As long as it's not audible, it has no practical meaning to me in and of itself. Also, luckily I'm also not gifted with golden ears so that's an advantage.

If it not audible, that is.

 

[MAB]

Many thanks for the offer! I will return, definitely. Maybe this weekend. I want to get everything started then, REW, UMIK, unpack a microphone stand I bought.
I will get the stuff out.Whether we take it here or via PM, we'll see.

Regarding the differences on my drivers. I don't fully trust my cheap multimeter that I bought at a cheap nick nack store.

The drivers were purchased used, so OP is right to be a bit paranoid....There may be a risk of that, paranoia

As stated by @Verdinut , there is a considerable manufacturing tolerance. If this is normal variation, the two tweeters should both measure acoustically close to each other. If 7% of the voice coil is shorted because you bought a used and abused pair of tweeters, then that will certainly show up in the acoustic measurements! And, 7% is quite large, as explicitly shown above.
The best part, this will be confirmed with acoustic measurements as you build these, and REW/UMIK will confirm. No need to lose sleep, or worry, and I am sure you will 'enjoy the music' after you enjoy building these speakers. Certainly willing to help you enjoy making acoustical measurements over the weekend, since that is what your thread is about. And of course, lots of tutorials on REW on ASR and all over the web.

 

[Verdinut]

As long as it's not audible, it has no practical meaning to me in and of itself. Also, luckily I'm also not gifted with golden ears so that's an advantage.

If it not audible, that is.

The difference within the 10% discrepancy is inaudible, except for the ones who have golden ears. If a serious double blind test was done for such situation, I am sure that nobody would hear a difference. Our ears are not as accurate as test equipment.

 

[MAB]

The difference within the 10% discrepancy is inaudible, except for the ones who have golden ears. If a serious double blind test was done for such situation, I am sure that nobody would hear a difference. Our ears are not as accurate as test equipment.

Agree with much of what you said. And, I am not a golden ear. And this is not about double blind testing discussion. This is about a pair of used tweeters that OP purchased that might be blown.
Where I agree: for instance +- 10% components in almost all crossover applications have no audible difference. Totally agreed. Maybe need to exclude certain notches, etc. But I am in strong agreement. And, when a spec sheet says "8 Ohms", the driver often has a DCR that is way different, like 5 Ohms. So, agreed there too.

But...

OP is worried they bought used tweeters online with a defective or blown voice coil. Partially shorted voice coils in overdriven tweeters is common. Changes of a few percent are common because of the geometry of the voice coil winding. And a tweeter with a 7% of the voice coil shorted is actually very audible. And dramatically measurable. Often has massive and shockingly audible distortion when driven hard.
And, used speakers sold online are sometimes blown.
And, OP's tweeters measure much different than each other.
And, I measured 21 drivers across 6 different groups, and the magnitude difference the OP sees would be an outlier in each of those groups. And, some of those groups involve speakers of same model manufactured 20 years apart.
So far, not enough data to tell if this is normal manufacturing tolerance, or shorted VC.
The great thing is, with REW and UMIK, OP will be able to compare the two tweeters with test equipment, which is the goal here. If shorted, will be obvious. And, likely the OP will be able to hear the difference in the REW sweeps. If this is part tolerance, the differences will be subtle at best, and not audible.

 

[Verdinut]

Agree with much of what you said. And, I am not a golden ear. And this is not about double blind testing discussion. This is about a pair of used tweeters that OP purchased that might be blown.
Where I agree: for instance +- 10% components in almost all crossover applications have no audible difference. Totally agreed. Maybe need to exclude certain notches, etc. But I am in strong agreement. And, when a spec sheet says "8 Ohms", the driver often has a DCR that is way different, like 5 Ohms. So, agreed there too.

But...

OP is worried they bought used tweeters online with a defective or blown voice coil. Partially shorted voice coils in overdriven tweeters is common. Changes of a few percent are common because of the geometry of the voice coil winding. And a tweeter with a 7% of the voice coil shorted is actually very audible. And dramatically measurable. Often has massive and shockingly audible distortion when driven hard.
And, used speakers sold online are sometimes blown.
And, OP's tweeters measure much different than each other.
And, I measured 21 drivers across 6 different groups, and the magnitude difference the OP sees would be an outlier in each of those groups. And, some of those groups involve speakers of same model manufactured 20 years apart.
So far, not enough data to tell if this is normal manufacturing tolerance, or shorted VC.
The great thing is, with REW and UMIK, OP will be able to compare the two tweeters with test equipment, which is the goal here. If shorted, will be obvious. And, likely the OP will be able to hear the difference in the REW sweeps. If this is part tolerance, the differences will be subtle at best, and not audible.

IMO, a partly shorted voice coil would be a very rare occurrence. As I said, a 10% reduction in DC resistance is nothing to worry about. Just listen to the damn thing and ask someone else to compare as well while listening to both drivers simultaneously one aside the other.

If the voice coil was blown, there wouldn't be any sound coming out of the speaker.

 

[MAB]

IMO, a partly shorted voice coil would be a very rare occurrence.

No. It actually isn't uncommon, depends on driver and use. And, OP bought the drivers used, so history isn't known. And, as I showed with measurements on over 20 drivers in several groups, 0.4 Ohm difference is abnormal.

As I said, a 10% reduction in DC resistance is nothing to worry about.

If due to part to part tolerance, yes. If due to shorted voice coil, there is definitely something to worry about.

Just listen to the damn thing and ask someone else to compare as well while listening to both drivers simultaneously one aside the other.

OP is building a speaker. You so funny saying "listen to the thing", especially because you make measurements when you build a speaker. Unless you are Chuck Norris...

The only remote possible audible difference would be that the lower DC resistance driver sounds slightly louder.

Yes, agreed if the different DCR was a result of (for instance) different wire resistivity. Not so if the manufacturer accidentally wired 7% different number of turns though. And certainly not if the VC is shorted between adjacent wires.

If the voice coil was blown there wouldn't be any sound coming out of the speaker.

No, as I said. And it's not uncommon, depending on the diver and the use. And it is audible. Back in the day, I replaced and repaired hundreds of blown car stereo tweeters. A significant percentage of them were overheated voice coil with adjacent wires shorted. They test lower DCR by 5% or more, just like OP is seeing. Drivers with this type of short sound bad in varying degrees, especially if driven hard. Even easier to measure just to take the uncertainty of our ear out.

The great news, Eighteen Sound knows that tweeters blow in all sorts of ways, and has replacement diaphragms for $20 euro. So this isn't the end of the world. And to be clear, OP either messed up the DCR measurement or likely has an overheated tweeter that got dumped online. A proper acoustic measurement with REW and UMIK for instance is actually what's called for. And since OP is building speakers, the measurements will happen. Possibly a good time to practice replacing tweeter diaphragms too!

 

[DanielT]

The great news, Eighteen Sound knows that tweeters blow in all sorts of ways, and has replacement diaphragms for $20 euro. So this isn't the end of the world. And to be clear, OP either messed up the DCR measurement or likely has an overheated tweeter that got dumped online. A proper acoustic measurement with REW and UMIK for instance is actually what's called for. And since OP is building speakers, the measurements will happen. Possibly a good time to practice replacing tweeter diaphragms too!

SuperDuper! Like Taco said.

I'm looking forward to getting REW and UMIK up and running this weekend. I study some instructional videos on Youtube for so long. But I'll be happy to get in touch with you when (not if, I know myself that well) things start to struggle for me with the installation this weekend.

This is going to be fun. And $20 / Euro for a new replacement diaphragm (if needed) is it more than worth it for me to get started with the measurements. Tuition money as it is called. Then I will measure the FR on a few more speaker elements.

 

[DanielT]

Now I have tried measuring some other speaker elements with my multimeter.

I was thinking of using these in some kind of budget three-way construction in the future, perhaps together with my Peerless SLS 10 basses.

According to the manufacturer : DC Resistance (Re) 3.2 ohms
(see attached image data sheet)

Dayton Audio - ND25FW-4 1" Soft Dome Neodymium Tweeter with Waveguide 4 Ohm

ND25FW-4 1" Soft Dome Neodymium Tweeter with Waveguide 4 Ohm

www.daytonaudio.com

My multimeter oscillates between 3.2-3.3 when I measure them. Exactly the same on both speaker elements:

____

This tc9, according to the manufacturer: DC Resistance-6.32 Ohm , 5%
(see attached image data sheet)

There, my multimeter oscillates between 6.2-6.3 and finally ends up at 6.2, for both elements:

XD125 , one still measures 6 Ohm, but I'll remove the solder and measure again since tonight. Not that I think it will make any difference, but I will try.


____
OT:

Check here, I thought this was bad by Dayton. Not marking the contacts +/- black/red on the tweeter ND25FW-4:

ND25FW-4 , tweeter. What are + and -? Red-black?

I was going to plug them in later today. But there is no marking on the connectors where I will attach speaker cables. The small bass element I have is excellent with red and black maked respectively, but nothing on these tweeters. One connector on the tweeter is a little narrower, see picture...

audiosciencereview.com

My tip with bass SLS 10 considering its low price and its power, use two in each speaker box. Especially if you have a slightly larger room. If you want to be fussy, you need to add a sub that digs down to 20 Hz, if you now want to reach the absolute lowest frequencies. If you are not satisfied with that far down in frequency, you can get a pair of SLS 10.

Seems to be a good budget driver:

Experiences of and / or measurements Peerless SLS series?

Seems to be speaker element with good performance - price ratio.:) You who have used these speaker elements, what are your experiences? Are there any distortion measurements on any of the elements in the SLS series? I tried to find some but I did not find any.

audiosciencereview.com

 

[Verdinut]

No. It actually isn't uncommon, depends on driver and use. And, OP bought the drivers used, so history isn't known. And, as I showed with measurements on over 20 drivers in several groups, 0.4 Ohm difference is abnormal.

If due to part to part tolerance, yes. If due to shorted voice coil, there is definitely something to worry about.

OP is building a speaker. You so funny saying "listen to the thing", especially because you make measurements when you build a speaker. Unless you are Chuck Norris...

Yes, agreed if the different DCR was a result of (for instance) different wire resistivity. Not so if the manufacturer accidentally wired 7% different number of turns though. And certainly not if the VC is shorted between adjacent wires.

No, as I said. And it's not uncommon, depending on the diver and the use. And it is audible. Back in the day, I replaced and repaired hundreds of blown car stereo tweeters. A significant percentage of them were overheated voice coil with adjacent wires shorted. They test lower DCR by 5% or more, just like OP is seeing. Drivers with this type of short sound bad in varying degrees, especially if driven hard. Even easier to measure just to take the uncertainty of our ear out.

The great news, Eighteen Sound knows that tweeters blow in all sorts of ways, and has replacement diaphragms for $20 euro. So this isn't the end of the world. And to be clear, OP either messed up the DCR measurement or likely has an overheated tweeter that got dumped online. A proper acoustic measurement with REW and UMIK for instance is actually what's called for. And since OP is building speakers, the measurements will happen. Possibly a good time to practice replacing tweeter diaphragms too!

So, you say that with a blown voice coil, there will be sound coming out of the driver? That's completely incorrect and impossible.
Have you ever built speakers? I have been for over 50 years. Over the years, I have seen surprising discrepancies in Thiele/Small parameters of various drivers. For example, I built several speaker systems using the pro audio Altec Lansing drivers. Some of their 8 ohm drivers showed variations in DC resistance between 5.6 ohms and 7 ohms. I've never heard of anyone complaining about their performance.
If the OP is worried about this DC resistance discrepancy, then he should return them for a refund and be over with.

 

[DanielT]

So, you say that with a blown voice coil, there will be sound coming out of the driver? That's completely incorrect and impossible.
Have you ever built speakers? I have been for over 50 years. Over the years, I have seen surprising discrepancies in Thiele/Small parameters of various drivers. For example, I built several speaker systems using the pro audio Altec Lansing drivers. Some of their 8 ohm drivers showed variations in DC resistance between 5.6 ohms and 7 ohms. I've never heard of anyone complaining about their performance.
If the OP is worried about this DC resistance discrepancy, then he should return them for a refund and be over with.

I'm mostly curious. Not too worried about it all.

Of course, removing the solder didn't matter. Still measuring 6 Ohms. Never mind, if I hadn't done that I would still have just wondered if it would have mattered.

 

[MAB]

So, you say that with a blown voice coil, there will be sound coming out of the driver? That's completely incorrect and impossible.

Actually, this is not correct. I even described how it happens (twice), perhaps you didn't read it. I saw other posters mention here too. Let me explain it again but maybe you won't read it anyway.
If a voice coil is overheated, two or more adjacent windings on the voice coil can short. These inter-winding shorts, the shorted windings no longer plays a role and the rest of the VC remains conductive. The reduction in resistance depends on the quantity of coils that got fused to each other. If 7% of the VC windings are shorted, the DCR reduces by ~7%, and the T/S parameters for the driver dramatically change (all of those shorted windings no longer play a role in the motor, inductance drops, and the defect introduces a non-linearity into the motor because the magnetic field in the vicinity of the short is quite non-uniform. Lots of stuff moves in this case, and the driver ends up testing much different than a good driver for the electrical parameters associated with the motor. Different drivers have different probability of this type of fail, some always blew to an open circuit, some have a large probability of the VC developing a partial short due to abuse. I have seen a few drivers with partial shorts due to misaligned VC rubbing the magnet.
And in case you don't want to read my text, here is a tutorial on voice coils that might help you visualize what is going on, and it touches on the problem of shorted turns, although more from the perspective of the type of bobbin the coil is wound on.

Voice Coils: A Tutorial

Mike Klasco (Menlo Scientific) provides an overview on how to specify or manufacture voice coils. In this reference article, Mike Klasco recaps on voice coil basics, bobbin materials and sizes, collars, winding techniques, configurations, tips and tricks and wire types and considerations - a...

audioxpress.com

Have you ever built speakers?

Yes I have. Perhaps you noticed I tested 22 drivers lying around my shop in this thread! It's not an accident! Back in the day, I installed thousands of car stereos, most built from separates. I worked at home hifi stores too, just slightly less blown tweeters! I can typically tell just from the sound if a driver has a VC rub or is partially shorted, so could all my co-workers. One thing for sure, if I got handed a pair of tweeter from the parts counter that were mismatched by 5%, no way I would begin the install... We tested every driver on an Ohm meter before install, no way you want to find out at the end of the build that you got a bad driver. So, yeah, experience. Literally thousands of drivers. YOu just don't see large DCR on a regular basis unless you measured wrong.

I have been for over 50 years. Over the years, I have seen surprising discrepancies in Thiele/Small parameters of various drivers. For example, I built several speaker systems using the pro audio Altec Lansing drivers. Some of their 8 ohm drivers showed variations in DC resistance between 5.6 ohms and 7 ohms. I've never heard of anyone complaining about their performance.

Perhaps you didn't abuse your tweeters the way some of my customers did! Interesting about your Altec Lansing drivers, I really don't know what to say about such a large mismatch without the data. Voice Coils are a length of wire wrapped into a precise number of turns. It is extremely unusual to see variation much larger than 1%, wire resistivity between samples, and hard to imagine the factory accidentally wound 25% more turns on the bobbin. It is very challenging to get the number of turns or the resistivity of the wire that different. In reality, VC matching is really quite precise, and not subject to large variation on a speaker that is working properly. That's why voice coil DCR variation is typically closer to 1% as I showed, not 7% as the OP measured, and certainly not 25% like you saw.