Impeadence rise?

[chad y 1]

Ok I was wondering what is the typical impeadence rise of voice coils?

this is why I ask. I have a TC sounds 3000 15 dvc 2 in a 3ft^3 sealed enclosure. I currently am running it in series to get a 4 ohm load on my Phoenix Gold Tantrum 1200.1, This amp is 2 ohm stable. now I have read that at rest most coils are under their rating (please correct me if I am wrong) so does this mean when power is put to them that thay rise to their stated ohm? maybe totally dependent on manufacture? enclosure size? sealed? vented?

my main question is is there a better way I should be wiring my sub to my amp? (or is this the best way)

if I wired in parallel would I get a 1 ohm load or would it rise higher?

Thanks

Chad

[johnecon2001 82]

DCR rises and drops depending on power applied at frequency.

You'll never have a perfect ohm load. Wiring that sub to 1 ohm is probably a bad idea if your amp is only 2 ohm stable.

[BKOLFO4 29]

DCR rises and drops depending on power applied at frequency.

That is not stated correctly. . .

DCR is DC resistance. When you measure a voice coil reistance with a DMM, you get DC resistance. This is the resistance everyone measures and then always asks "why are my 2 ohm coils only 1.4?".

Impedance is what you get when AC voltage is applied and it varies with frequency. Since a voice coil is wound like an inductor, the impedance with AC applied will not be the same as the DC resistance. There are multiple ways to measure the driver's impedance at a given frequency. If you have a clamp on current meter, you can measure the voltage and current playing a test tone to get the impedance at a given frequency.

Impedance rise occurs when the driver is placed in the enclosure. The impedance at a given frequency will more than likely change if measured free-air vs. in the enclosure, since the coil will react differently with back pressure applied to the cone. Once again, the only way to know how much this change will be for your system is to measure it.

You can do a search to find hundreds of articles on impedance vs. resistance.

http://www.teamrocs.com/technical/pages/re...e_impedance.htm

Brian

[chad y 1]

thanks for the information.

[Guest zedman]

that just explained a question I have been pondering. Z

[007 0]

static coil is just a resistor, once it moves you have two components, a resistive component R and a reactive component Z , the details about how Z is works falls under AC circuit analysis and you'll need some knowledge of inductors and capacitors. but what my point is is simple impedance rise generally refers to one of the more complex parts of a dynamic transducer. sure you get this massive impedance peak at resonance, but there is another, more sublet effect that is also happening. Current thu the voice coil creates a magnetic field. This field moves and that can be calculated as a rate of change of magnetic flux, divide that quantity by current and we have exactly an inductor. This inductor is created from the coil and the inductive core of the motor which consists of steel (mostly) and air. Now, you probably guessed that this is probably not what a speaker is designed to too, and its a good thing the inductive core is poor, but it can't be ignored either. Moreso the inductor created from this circumstance is non-linear! Steel is lossy (conductive) so the inductance drops over time on its own without being discharged. This lossy inductor is very difficult to model accurately, but one of the interesting things that does occur is the impedance is affected by this as the frequency becomes higher and higher. Ideally, you would see a flat impedance curve. With an inductor you will see a rising impedance curve but generally pretty linear and then finally with a non-linear inductor, we get this non-linear curved rising impedance curve. Its not uncommon for say a high inductive woofer to be up to 10 or even 20ohms again by the time it hits 20,000Hz. This is exactly why woofers are bad for high frequency stuff, its really not as much a mass issue as it is an electrical issue.

now when mfr's say 4 ohm nominal, 3 ohm Dcr for example, this generally means that impedance never really dorp all the way back to their DCR after resonance. this is largely because of the inductance already playing a minor role in the speakers sensitivity. An impedance minimum may occur at 50Hz for example in some system, and we already may experience some small % of increase from the inductance. Its important to keep inductive low for sensitivity reasons.

transient or time-domain effects such as current-lag necessarily affect things in the frequency domain, thats why they are important to understand, but don't get caught up on this like "good" transients because you'll never ever ear that stuff on its own. It really just affects other things. I dont care who you are, you can't hear current lag, but you can indeed here a loss of 1dB. And there are many more complex distortion components to a driver than just inductive ones, Klippel has a pretty extensive list, most have to do with some value with respect to displacement.

[95Honda 486]

Ugghh...

There is no such thing as IMPEDANCE RISE.

If you have a driver, in or out of a box, it will have an impedance that fluctuates with frequency, this isn't impedance rise, it is an impedance curve, and has been that way longer than anyone of us on here has been alive.

DCR has less to do with impedance than almost everyone thinks. Measuring DCR tells you that you don't have a shorted or open coil, and ROUGHLY, I mean VERY roughly what the impedance MAY average.

If you don't have an impedance bridge, or something like a Dayton Woofer tester, you, nor anyone else will be able to tell you what your impedance is. You can clamp current and check voltage a hundred times if you feel like it, because that is what you would have to do to plot your impedance without the other things mentioned. And you would have to do it a BUNCH of times...

Plan on this, if the manufacturer tells you it's a 4 ohm woofer, there is 99% chance that your impedance will hardly ever drop below this. It will be above this the rest of the time due to the box and the Le of the voice coil. It is impossible (unless you short windings) to have an impedance on any frequency above .00001 Hz that will be less than the DCR.

The guys that are "Strapped at .35 ohms" are more at 2+ ohms most of the time... This is due to the box, the Le of the driver, the frequency, the heat of the coils, the resistance of the cables and all the connections, etc.....

This why amps that are run at low inpedance will shut off or blow with some songs and not others or sine waves instead of songs, it is all due to the varing impedance and phase magnitude the load presents.

Your 1 ohm subs could be 20 ohms at certain frequencies in cerertain boxes... Things really get screwy around tuning and/or resonance...

[BKOLFO4 29]

static coil is just a resistor, once it moves you have two components, a resistive component R and a reactive component Z.

It really is not if it is in static position, it is if you have DC current or AC current. DC current, the resistance is the coil's DCR, AC current is the impedance with the 'Z' portion as you described.

Apply DC (like a 9 volt battery) to a coil and the cone will jump, but the coil resistance is still the DCR.

There is no such thing as IMPEDANCE RISE.

But the measured impedance at a given frequency will be different for a driver in and out of the box. Every time I have ever measured it, it is always higher with the woofer in the box. . . Do you not agree??

Brian

Edited July 16, 2008 by BKOLFO4

[95Honda 486]

I agree 100%.

But this isn't "Impedance Rise". It is a free-air impedance curve vs a system alignment curve. I guess what I am trying to get people to understand is there is no such technical term as "Impedance Rise".... This is becuase the impednace goes up, it goes down, it goes up again.... Etc Etc Etc... And this is an impedance curve.... Not "Impedance Rise"

I guess peole will just have to let the whole DCR = Impedance thing go.... It will be hard... But they can do it!

[jonbearsmt 919]

i like you guys.

[007 0]

Ugghh...

There is no such thing as IMPEDANCE RISE.

If you have a driver, in or out of a box, it will have an impedance that fluctuates with frequency, this isn't impedance rise, it is an impedance curve, and has been that way longer than anyone of us on here has been alive.

DCR has less to do with impedance than almost everyone thinks. Measuring DCR tells you that you don't have a shorted or open coil, and ROUGHLY, I mean VERY roughly what the impedance MAY average.

If you don't have an impedance bridge, or something like a Dayton Woofer tester, you, nor anyone else will be able to tell you what your impedance is. You can clamp current and check voltage a hundred times if you feel like it, because that is what you would have to do to plot your impedance without the other things mentioned. And you would have to do it a BUNCH of times...

Plan on this, if the manufacturer tells you it's a 4 ohm woofer, there is 99% chance that your impedance will hardly ever drop below this. It will be above this the rest of the time due to the box and the Le of the voice coil. It is impossible (unless you short windings) to have an impedance on any frequency above .00001 Hz that will be less than the DCR.

The guys that are "Strapped at .35 ohms" are more at 2+ ohms most of the time... This is due to the box, the Le of the driver, the frequency, the heat of the coils, the resistance of the cables and all the connections, etc.....

This why amps that are run at low inpedance will shut off or blow with some songs and not others or sine waves instead of songs, it is all due to the varing impedance and phase magnitude the load presents.

Your 1 ohm subs could be 20 ohms at certain frequencies in cerertain boxes... Things really get screwy around tuning and/or resonance...

http://users.ece.gatech.edu/~mleach/papers/vcinduc.pdf

page 447

look at the impedance graph model (it was done in pspice)...... it increases a lot with respect to frequency, that's what i was referring to, and that i what i would call a rising impedance curve... this is an inductance issue.

perhaps we're talking about different things?

Edited July 18, 2008 by 7

[95Honda 486]

Yes, we are talking about different things. You are talking about an actual impedance rise in respect to frequency due to inductance, that isn't what I have been refering to, and this also isn't really dependant upon the box.

I am talking about the term "Impednace Rise" that gets thrown around here 10 times a day, when people are actually talking about thier box impedance, which goes up and DOWN, hense "Impedance Rise" is not correct...

[chad y 1]

thank you all for your information. when I started this thread I was trying to learn and to get the most out of my system. I have learned quite a bit. I still have my sub wired in series to my tantrum 1200.1 I have however built a vented box and was amazed at the output difference.

once again thanks for all the information

Chad

[007 0]

drop it to one ohm (parallel) and turn the gain down a touch...see if it works

you should be able to get more current which is what you need.

[BKOLFO4 29]

I guess peole will just have to let the whole DCR = Impedance thing go.... It will be hard... But they can do it!

I don't think they can.