Voice Coil Wiring and Transient Response

Hey Guys (and Gals),

I'm just thinking out loud here, so please feel free to correct me. Working this out on my own limits me to what I can figure out. I'm sorry that it's in a bit of a mixed up order. These thoughts just kept flowing, and I'd like some answers to them.

First, inductance is a function of impedance. Lowering impedance (resistance, in ohms) lowers induction.

Secondly, acceleration of a driver is a function of the current through the driver.

Third, an amplifier is only capable of outputting up to a certain voltage. It's the current that changes, which allows an amp to have varying power outputs for various impedances. When increasing the impedance, the current must drop to maintain the same power output. Since the amp has a maximum voltage it can output, the impedance must drop to maintain the higher currents through the driver.

Would wiring a DVC driver in series vs parallel change the driver's induction, and therefore the driver's transient response, right? For optimum system response, when the option is available, is to have two DVC drivers wired in parallel and then wired into series together, rather than the other way around, correct? You'd get the same final load to the amplifier, but because of the higher impedance, there's higher induction and poorer response.

Ultimately, it boils down to the fact that it's better to have a driver wired in parallel rather than series, if all other factors are equal, correct? And to extend that, two drivers, with all else being equal that have different impedance in their coils (ie: dual 2-ohm versus dual 4-ohm), the dual 2-ohm will have better transient response when receiving the same power, when each is wired into parallel.

Finally, I heard a rumor that dual 4-ohm drivers were "better" choices than dual 2-ohm drivers, all else being equal. Why would that be, if they are less responsive?

Feel free to correct me, or let me know of other things I'm missing. I'm trying to learn all of this on my own, and am having a fun time of it.

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'91 Honda Prelude

Some reading for you:

https://www.adireaudio.com/Files/TechPapers/WooferSpeed.pdf

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That's what I read, and by reading that I got these questions. I'm pretty clear on the definitions of everything, but not 100%, which is why I asked.

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'91 Honda Prelude

Inductance is the ratio of generated magnetic flux to current.  That ratio is fixed for any magnetic system once it is built.  As current flow increases or decreases due to changes in impedance, the gross magnetic field strength changes, but the ratio of the amount of flux produced per unit current flow does not change.  So, while you can change the impedance (resistance to AC current flow) by changing the external wiring, you cannot change the inductance of the coils.

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But wouldn't a DVC driver have greater current when in parallel than in series, or is it that the source (ie: ampliifer) is able to feed more current to the parallel driver because of the lower impedance, and the inductance would be the same no matter how it's wired as long as the amp can give the same power?

How about the dual-2 versus dual-4 question?

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'91 Honda Prelude

Like I said, the inductance at any given frequency is fixed and determined by the physical geometry,materials, etc. of the voice coil/magnet system.  Changing the current flow by changing the impedance will change the magnetic field strength, but not the inductance.  To vary the inductance you'd have to change the coil turns or spacing or materials, or change the core or core position in a solid-core inductor. (Loudspeaker inductance does change with frequency, but that's independant of any resistance changes as well.)

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Alright, works for me.

Now, what about 2-ohm vs. 4-ohm voice coils? They have different physical geometry, all else being equal, and so would have different Ts parameters, no? What are the performance differences between them, or is it up to the manufacturer to compensate between the two when designing and manufacturing the different drivers?

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'91 Honda Prelude

There is no inherent performance difference between 2-ohm and 4-ohm coils, it all depends on the loudspeaker system design.  But, all else being equal, a 2-ohm VC and a 4-ohm VC will have different T/S parameters, correct.  Which will perform better?  Neither, necessarily.  You can't tell by simple VC impedance numbers alone.  The answer is "It Depends."  Besides, you can create a 2-ohm and a 4-ohm coil with nearly identical inductance simply by using different ohms/foot resistance wire in the coil winding process.   Check the Le and the Qes of the same loudspeakers with different VC impedance to see how it has changed.

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dj_mittens wrote:

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Hey Guys (and Gals),

I'm just thinking out loud here, so please feel free to correct me. Working this out on my own limits me to what I can figure out. I'm sorry that it's in a bit of a mixed up order. These thoughts just kept flowing, and I'd like some answers to them.

First, inductance is a function of impedance. Lowering impedance (resistance, in ohms) lowers induction.

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1: No. And yes. They are really a hand-in-hand relationship. You can't have one without the other. Impedance is a complex resistance involving all of the factors in a voice coil - resistance, inductance and capacitance, so there is the "no" part... impedance is a function of inductance. As an example of this, the planer magnetic drivers I have in my house are VERY low inductance and capacitance, yet they present an almost constant (DCR) of 4 ohms to the amplifier - no impedance peaks or dips.

2: To lower the inductance of a voice coil will NOT NECESSARILY mean that you lower the resistance. A geometry change is required for this to happen. However, by reducing the number of turns in a voice coil, you WILL reduce the inductance, but if you use smaller wire, the inductance will change little, but the resistance will go up accordingly. You can also keep the wire size the same - to maintain power handling, but by enlarging the voice coil diameter, you will reduce the number of turns around that iron pole piece. This will also reduce your inductance, without changing the resistance of the coil. The impedance MAY change. Most likely, the impedance PEAKS/DIPS will change, while the net impedance of the driver will remain pretty close to what it was... You will come closer to a DCR - an ideal load for an amplifier.

dj_mittens wrote:

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Secondly, acceleration of a driver is a function of the current through the driver.

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Yes. It is called AMP TURNS. The more wire you can have in a voice coil RIGHT IN THE MAGNETIC FIELD, the better your efficiency will be. Short, multi-layer voice coils are perfect examples of this. Herein squats the toad. The more turns you have in a short voice coil - to keep as many turns as possible in the magnetic field - the higher your inductance. There goes your transient response. Additionally, there goes your Xmax, as well. This is one of the dilemmas that keep speaker designers like Dan Wiggins, of Adire Audio fame, awake at night. can you add more turns on a longer coil? Yes, but add the corresponding inductance increase (due to the additional turns of wire) and the additional mass (due to the bigger former and added wire weight), and you end up with an inefficient, slow driver - BUT you gain Xmax.

dj_mittens wrote:

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Third, an amplifier is only capable of outputting up to a certain voltage. It's the current that changes, which allows an amp to have varying power outputs for various impedances. When increasing the impedance, the current must drop to maintain the same power output. Since the amp has a maximum voltage it can output, the impedance must drop to maintain the higher currents through the driver.

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Well, if you increase the impedance, your amp CANT make the same amount of power. Power equals voltage times current, right? High resistance equals low current. You have to increase the voltage (electromotive FORCE) at the amp terminals to FORCE the current through the voice coil, if you raise the impedance. This is why the drive for lower and lower impedance voice coils. Easier to make current than voltage. I am certain you already understand that if you halve the impedance, you double the power, right? Well the opposite also holds true. If you double the impedance, you halve the power.

dj_mittens wrote:

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Would wiring a DVC driver in series vs parallel change the driver's induction, and therefore the driver's transient response, right? For optimum system response, when the option is available, is to have two DVC drivers wired in parallel and then wired into series together, rather than the other way around, correct? You'd get the same final load to the amplifier, but because of the higher impedance, there's higher induction and poorer response.

Ultimately, it boils down to the fact that it's better to have a driver wired in parallel rather than series, if all other factors are equal, correct? And to extend that, two drivers, with all else being equal that have different impedance in their coils (ie: dual 2-ohm versus dual 4-ohm), the dual 2-ohm will have better transient response when receiving the same power, when each is wired into parallel.

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The number of turns of wire do not change, regardless of series or parallel wiring, so you will have minimal effect on overall inductance, so you can shoot that theory in the foot as well.

dj_mittens wrote:

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Finally, I heard a rumor that dual 4-ohm drivers were "better" choices than dual 2-ohm drivers, all else being equal. Why would that be, if they are less responsive?

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The rumor part, I think, comes from the "better" portion of it. Amps that are stable to 2 oms per channel are a dime a dozen today, as are 1 ohm stable mono amplifiers. Dual 4 ohm cols will provide more "safe" wiring options for more amplifiers available today - 8 ohm, 4 ohm, and 2 ohm wiring options (per woofer) - and 4 ohm, 2 ohm, and 1 ohm options with multiple woofers. Not that the rumor is completely "wrong", but if the d2o and d4o woofers are dsigned SIMILARLY, there won't be (or, at a minimum, SHOULDN'T be) a tremendous effect on transient response...

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Awesome! Thank you so much DYohnand haemphyst. I'm starting to understand all of this. Thanks for bearing with me, and not flaming me (as is wont to happen in certain less mature forums).

I'll try to hang out more and contribute if I can. Again, thanks for starting me on the right path.

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'91 Honda Prelude

haemphyst wrote:

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Yes. It is called AMP TURNS. The more wire you can have in a voice coil RIGHT IN THE MAGNETIC FIELD, the better your efficiency will be. Short, multi-layer voice coils are perfect examples of this. Herein squats the toad. The more turns you have in a short voice coil - to keep as many turns as possible in the magnetic field - the higher your inductance. There goes your transient response. Additionally, there goes your Xmax, as well. This is one of the dilemmas that keep speaker designers like Dan Wiggins, of Adire Audio fame, awake at night. can you add more turns on a longer coil? Yes, but add the corresponding inductance increase (due to the additional turns of wire) and the additional mass (due to the bigger former and added wire weight), and you end up with an inefficient, slow driver - BUT you gain Xmax.

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Oddly enough Dan Wiggins loses a lot less sleep at night than other engineers because he has the best answer to this dilema.  The XBL^2 motor he helped invent is much more flux efficient than other motor topologies for a given excursion.