Any way to manipulate the overal impedance(ohms)?

[duanebro 10+ year member]

You are asking if anyone here has a Klippel machine, which I doubt. People like Sundownz has access to one Im sure, but they aren't something the average DIY'er here will have and can run the testing you request. Besides, it is unnecessary to discuss the topic at hand, simple physics answers most of the questions in this thread.

LOL, sorry, I ment a woofer tester. Or LIMP. These can measure T/S specs in seconds. Klippel isn't needed as the bl curve and xmax, and things of that nature are not going to change.

 

[audioholic 5,000+ posts]

LOL, sorry, I ment a woofer tester. Or LIMP. These can measure T/S specs in seconds. Klippel isn't needed as the bl curve and xmax, and things of that nature are not going to change.

The BL curve wont change, but the BL would. As would most other t/s specs. xmax is one of the few specs that would remain unaltered by using only one coil in a DVC.

 

[duanebro 10+ year member]

The BL curve wont change, but the BL would. As would most other t/s specs. xmax is one of the few specs that would remain unaltered by using only one coil in a DVC.

Yes, the bl would change. The point I am trying to make is that klippel is not needed to test if shorting the coil makes a difference.

 

[audioholic 5,000+ posts]

The point I am trying to make is that klippel is not needed to test if shorting the coil makes a difference.

No woofer tester of any type is needed to know that it will make no difference. I explained why above.

 

[bubbagumper6 5,000+ posts]

.... not meaning to. I have a problem with this type of discussion where I sound like a dikk... but I'm really not trying to be. With that said, a stepping transformer is one coil wrapped inside of another coil with an iron core in the middle. (this simply improves magnetic strength as you know). The coil being powered will have a certain number of turns. The second coil has a certain number of turns. The number of turns is the ratio of the stepping. So if it's a "step up" transformer, the first coil will be powered let's say by 12v. If it's a 1:3 step up, the second coil will have 3x the turns as the first one it will have 36 volts vdc, with the current also reduced proportionally. NOTHING moves.With that being said, the similarities to what we are talking about are many.

Yep yep, I knew all that, took an entire class based on transformers (electrical energy conversion). I wasn't really referring to the energy being transferred through the core, I was talking about the voltage generated on the second coil from simply being moved through the magnet's magnetic field. I wasn't trying to imply I thought this would change the woofer specs in any way, mostly because I don't know a lot about T/S parameters, I was just trying to say I thought it might have an effect because moving an open circuited coil through the field is different than moving a closed (shorted) circuit coil.

I know I can be a dick sometimes too but when it comes to the more knowledgeable members I try to maintain respect (especially outside the dome) because I like to learn.

Also I have a side question for anyone who wants to field it. The first woofers I ever bought were a pair of JL12W3v2's and their manual had a huge warning in it basically stating if you run the subs using only one coil you could seriously damage the woofer and your warranty was instantly void. What exactly could be damaged by running only one coil?

 

[audioholic 5,000+ posts]

Yep yep, I knew all that, took an entire class based on transformers (electrical energy conversion). I wasn't really referring to the energy being transferred through the core, I was talking about the voltage generated on the second coil from simply being moved through the magnet's magnetic field. I wasn't trying to imply I thought this would change the woofer specs in any way, mostly because I don't know a lot about T/S parameters, I was just trying to say I thought it might have an effect because moving an open circuited coil through the field is different than moving a closed (shorted) circuit coil.
I know I can be a dick sometimes too but when it comes to the more knowledgeable members I try to maintain respect (especially outside the dome) because I like to learn.

Also I have a side question for anyone who wants to field it. The first woofers I ever bought were a pair of JL12W3v2's and their manual had a huge warning in it basically stating if you run the subs using only one coil you could seriously damage the woofer and your warranty was instantly void. What exactly could be damaged by running only one coil?

JL placed that warning to simply keep people from thinking they could only hook up one coil, but still maintain the same thermal limits on the subwoofer. When only using one coil, thermal limits are cut (almost) in half. JL is notorious for covering their bases to keep from looking like they sell bad equipment due to poor installs, that's all that warning was meant to do.

 

[maylar 10+ year member]

.... not meaning to. I have a problem with this type of discussion where I sound like a dikk... but I'm really not trying to be. With that said, a stepping transformer is one coil wrapped inside of another coil with an iron core in the middle. (this simply improves magnetic strength as you know). The coil being powered will have a certain number of turns. The second coil has a certain number of turns. The number of turns is the ratio of the stepping. So if it's a "step up" transformer, the first coil will be powered let's say by 12v. If it's a 1:3 step up, the second coil will have 3x the turns as the first one it will have 36 volts vdc, with the current also reduced proportionally. NOTHING moves.With that being said, the similarities to what we are talking about are many.

In a transformer, the magnetic field "moves", expanding and contracting with the AC current applied to the primary. A transformer will not "step up" or "step down" DC current. The magnetic field must cut across the coil windings to induce any voltage on the secondary.

Connect a fixed DC source (battery) to a transformer. You will get a spike of output voltage for the time it takes for the transformer's inductance to charge (changing current, moving magnetic field). But once current becomes steady, there's no more output on the secondary. Then remove the battery, and as the magnetic field collapses ("moves") there is output on the secondary. This is exactly how an automotive ignition coil (which is a step-up transformer) works.

The same is true with a coil in a fixed magnetic field. If the coil is not moving there will be no induced voltage. Like a generator that's not turning.

 

[audioholic 5,000+ posts]

In a transformer, the magnetic field "moves", expanding and contracting with the AC current applied to the primary. A transformer will not "step up" or "step down" DC current. The magnetic field must cut across the coil windings to induce any voltage on the secondary.
Connect a fixed DC source (battery) to a transformer. You will get a spike of output voltage for the time it takes for the transformer's inductance to charge (changing current, moving magnetic field). But once current becomes steady, there's no more output on the secondary. Then remove the battery, and as the magnetic field collapses ("moves") there is output on the secondary. This is exactly how an automotive ignition coil (which is a step-up transformer) works.

The same is true with a coil in a fixed magnetic field. If the coil is not moving there will be no induced voltage. Like a generator that's not turning.

Agreed. But the question involves the coil moving, not stationary (since the first coil would be powered, thus causing motion). But its been suggested the field generated in the second coil would create a situation in which the Qes remains the same as if both coils were powered, which is of course incorrect.

Thanks for the educated reply.

 

[bubbagumper6 5,000+ posts]

In a transformer, the magnetic field "moves", expanding and contracting with the AC current applied to the primary. A transformer will not "step up" or "step down" DC current. The magnetic field must cut across the coil windings to induce any voltage on the secondary.
Connect a fixed DC source (battery) to a transformer. You will get a spike of output voltage for the time it takes for the transformer's inductance to charge (changing current, moving magnetic field). But once current becomes steady, there's no more output on the secondary. Then remove the battery, and as the magnetic field collapses ("moves") there is output on the secondary. This is exactly how an automotive ignition coil (which is a step-up transformer) works.

The same is true with a coil in a fixed magnetic field. If the coil is not moving there will be no induced voltage. Like a generator that's not turning.

I thought this earlier (that you could only supply a transformer with AC) but couldn't remember if there were any applications where DC could be used. It's been a little too long since I took that energy conversion class, haha.

 

[ahole-ic]

ecrack just likes to run his mouth and the users who don't know any better think he's smart. It seems to be working well for him as I see his name mentioned in the "Smartest Member Thread" lol

Why was that necessary?

 

[ahole-ic]

In a transformer, the magnetic field "moves", expanding and contracting with the AC current applied to the primary. A transformer will not "step up" or "step down" DC current. The magnetic field must cut across the coil windings to induce any voltage on the secondary.
Connect a fixed DC source (battery) to a transformer. You will get a spike of output voltage for the time it takes for the transformer's inductance to charge (changing current, moving magnetic field). But once current becomes steady, there's no more output on the secondary. Then remove the battery, and as the magnetic field collapses ("moves") there is output on the secondary. This is exactly how an automotive ignition coil (which is a step-up transformer) works.

The same is true with a coil in a fixed magnetic field. If the coil is not moving there will be no induced voltage. Like a generator that's not turning.

You're right in that the voltage must change. It could be done with dc if the voltage oscillated, but it would generate lots of heat and would need to be liquid cooled so the question is why? That nuance doesn't change the point of my comments.

 

[maylar 10+ year member]

You're right in that the voltage must change.

The magnetic field must change.

It could be done with dc if the voltage oscillated,

An oscillating DC voltage is... wait for it... AC

but it would generate lots of heat and would need to be liquid cooled so the question is why?

Umm.. OK. I must've missed that part during the 7 years that I designed DC-DC converters for a living. Whatever.

That nuance doesn't change the point of my comments.

I was respoding to your question about the operation of a transformer, and your incorrect assertion that "NOTHING moved". As I said, the magnetic field moved. That "nuance" is rather important in this context.

 

[ahole-ic]

The magnetic field must change.

You proved with your last post that the voltage must fluxuate... why would you change it now?

An oscillating DC voltage is... wait for it... AC

That isn't true. I double checked before I posted because I knew someone would say that. I thought you had significantly more knowledge so I didn't assume it would be you to say this. A dc circuit that in regular intervals raises and lowers the voltage does not make it AC. It DOES make it oscillating DC. The difference would obviously be that the polarity would change with each cycle. In this case we're not talking about the polarity changing... again I'm sure you know this so I really don't understand your wildly inaccurate comment.

Umm.. OK. I must've missed that part during the 7 years that I designed DC-DC converters for a living. Whatever.

So if you apply a constant DC current to a tiny coil it will handle it indefinitely? I'm pretty sure dc current is a common killer of subwoofer voice coils. We have no reason to believe that it wouldn't kill a coil in a transformer without special cooling.

I was respoding to your question about the operation of a transformer, and your incorrect assertion that "NOTHING moved". As I said, the magnetic field moved. That "nuance" is rather important in this context.

That's fine. I'm not offended. Getting to the correct answer is really all that matters.... me being right isn't. I thought we were having a discussion... why would you get defensive all of a sudden? I believed bubba to be saying that the coil must move in and out of the magnetic gap. That doesn't happen in transformers. Nothing physically moves. The magnetic field develops and collapses......

 

[maylar 10+ year member]

Agreed. But the question involves the coil moving, not stationary (since the first coil would be powered, thus causing motion). But its been suggested the field generated in the second coil would create a situation in which the Qes remains the same as if both coils were powered, which is of course incorrect.
Thanks for the educated reply.

Funny how a thread morphs into a new topic, eh? I wonder if the OP is still following this //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif

I'm not a speaker guy, so I'll leave the Qes stuff to you and others. I am however an EE, and I have a fair knowledge of electromagnetic induction and motor action. A few points that are worth mentioning in the context of this thread:

Any permanent magnet motor can be used as a generator. Apply mechanical energy and the motor puts out a voltage. The more load you put on a generator, the more energy it takes to move it. A speaker can be both a motor and a generator - think about intercoms that use the speaker as a microphone.

If you short out the voice coil of a speaker it will take more effort (energy) to move the cone through the magnetic field. Whether you can discern that by "tapping' on the cone I don't know. But actually pushing on it you WILL feel more resistance.

If you power a DVC sub with just one coil, the voltage across the unused coil will be exactly the same as the voltage across the powered coil. You have the same number of turns traveling at the same rate through the same magnetic field. It's a generator. Now if you short out the unused coil, current will flow. Power will be consumed. That power must come from the amplifier. More input current, same voltage, means the impedance that's reflected back to the amplifier is lower. This is Physics 101.

Try this experiment - power up a DVC sub on just one coil with some 50-60 Hz level and measure the voltage and current. You will find that the voltage on the open coil is the same as what's on the powered coil. Now short out the unused coil. The current into the powered coil will double. It's exactly the same impedance to the amplifier as running both coils in parallel.

So Qes aside, the original question should be answered that if you want to change the impedance of your sub by running only one coil, you should NOT short out the unused coil.

I think I'll have another glass of Merlot now... hic...

 

[maylar 10+ year member]

That's fine. I'm not offended. Getting to the correct answer is really all that matters.... me being right isn't. I thought we were having a discussion... why would you get defensive all of a sudden? I believed bubba to be saying that the coil must move in and out of the magnetic gap. That doesn't happen in transformers. Nothing physically moves. The magnetic field develops and collapses......

OK, I understand. My apologies for being a dik.