Question about dual voice coil drivers.

[RMutt]

I have a 12" dual voice coil driver. Both coils are 8 ohms. At the moment it is connected for just one voice coil, the other is just idle. I realise I cannot wire them in series or parallel because this doubles or halves the impedance, but I believe there is another option, to short the other voice coil. My question is, if I go for the last option, how would this affect the sonic behavior of the driver? Please don't say try it and see, I don't want to take everything apart again if I am going to be wasting my time!

[Firebottle]

Do not short the 2nd voice coil :eek:

The two coils will act like a transformer and present a very low impedance to the amp (certainly at high frequency) if the 2nd coil is shorted.

You can connect the coils in series or parallel but you have to get the phasing correct.
If you have an amp that will drive 4 ohms then you can get twice the power.

For parallel operation connect the two +ves together and the two -ves together.
For series 16 ohm operation feed into one +ve and the 2nd -ve, then link the other + and -.

:cool: Alan

[RMutt]

Thanks Alan. No, my amp won't do 4 ohms. This is where I read about shorting the spare coil. http://www.diy-audio.narod.ru/litr/DualVoiceCoilDrivers.pdf

[Barry]

That site is written in Cryllic!

But I would agree with Firebottle - shorting out the second coil will severely dampen the speaker motion. Driving current through the first coil causes the speaker to become a motor (like all speakers), however the second coil will be part of a generator and so there will be a potential difference across its terminals. Shorting these terminals will therefore damp the speaker.

I'm not sure if the AC flux linkage between the two coils is sufficiently strong for them to be regarded as forming a transformer. But regardless of this - leave the second coil open circuit.

[RMutt]

Ha ha. I see what you mean Barry. I bet there's some really interesting stuff there, if we could read it. I don't know how that happened, but if you click the hotlink on the page you first get to, the stuff I read is there.

[Barry]

Just read the link. He seems to be saying exactly the same as my post, save he thinks the dampening effect, through shorting out the second voice coil, will reduce the Q-value of the speaker's natural resonance. Well it will, but I'm not sure if it is the best way to do it.

We have other members here who know more about these matters than I. Perhaps they might offer their views.

[RMutt]

Thanks for taking the time to read it. Any ideas what this 'dampening' effect might mean to the sound?

[walpurgis]

What would be the effect of putting a capacitor across the second coil winding?

[Barry]

What would be the effect of putting a capacitor across the second coil winding?

To be honest, I'm not sure. Suspect there would still be some dampening effect, as the capacitor was alternatively charged and discharged with each half cycle.

No doubt it would depend on the coil inductance and resistance, and the size of the capacitor.

[walpurgis]

Hi Barry, would the capacitor not act like an HF filter, rolling off the bass unit due to increasing active resistance as frequency rises?

[Barry]

Hi Barry, would the capacitor not act like an HF filter, rolling off the bass unit due to increasing active resistance as frequency rises?

The opposite would happen: the capacitor has a reactance which is inversely proportional to frequency. Thus the capacitor would more readily shunt the coil at high frequencies.

It's complicated and all depends on the relative resistances and reactances. Will the system be operating above or below the LC resonant frequency?

Perhaps Mark (Reid Malafant) might be able to answer your query.

Regards