How To Increase Driver Nominal Impedance?

[Jay]

I have some 4 Ohm woofers that I want to use for 3-way. But because of the low impedance they are not so useful so I want to increase this nominal impedance by modifying it. Any suggestion on how I better do that? Here is what I want to do:

1) Change the wire of the voice coil using smaller diameter/gauge cable. Could be the same number of layer, or more if can be done without increasing the coil gap size.

2) Add more layers to the winding. The gap size will be made bigger to accommodate this change.

3) I don't want to increase the length of the coil winding (to avoid distortion)

Thanks

[AndrewT]

wire two identical 4ohm driver voice coils in series to give an effective 8ohm loading.

[Jay]

Originally Posted by AndrewT

wire two identical 4ohm driver voice coils in series to give an effective 8ohm loading.

Can I add only the coil (not the driver) in series? How much power/sensitivity is lost compared to adding a 8-ohm resistor? I think it wont work But never tried it before. I have to try it (even only once) just for the sake of experiencing it

[activexp]

Originally Posted by Jay

I have some 4 Ohm woofers that I want to use for 3-way. But because of the low impedance they are not so useful.... )

Thanks

Why does the low impedance make them not so useful? Isn't modifying the driver a bit extreme? A bit risky I would have thought. If the mid and tweeter are 8 ohm and the XO designed correctly I can't see any problem with 4 ohm woofers. Unless I'm missing something

[gedlee]

Originally Posted by Jay

Can I add only the coil (not the driver) in series? How much power/sensitivity is lost compared to adding a 8-ohm resistor? I think it wont work But never tried it before. I have to try it (even only once) just for the sake of experiencing it

Any resistance that is added in series with the coil that is not linked to the flux for better driving force, lowers the efficiency.

And I would caution you about changing the coil unless you have a lot of experince at this - it is not an easy thing to do.

But, if you are insistant in changing the coil, then generally a smaller guage wire with more turns will result in basically the same efficiency at a higher impedance. You really can't change the gap on an assembled speaker - thats not possible, or at least not reasonably.

[Jay]

Originally Posted by gedlee

And I would caution you about changing the coil unless you have a lot of experince at this - it is not an easy thing to do.

Actually I have some experience with this, but changing from small gauge wire to bigger gauge wire to "improve" the bass. Now I want to do the opposite to increase the impedance.

Originally Posted by gedlee

But, if you are insistant in changing the coil, then generally a smaller guage wire with more turns will result in basically the same efficiency at a higher impedance. You really can't change the gap on an assembled speaker - thats not possible, or at least not reasonably.

Yes, it is not difficult to change the gap size, because the outer ring is usually only around 3 mm thick. I have done this before.

BTW, thank you for confirming or giving the green light for proceeding with the plan. Actually I'm hoping there is other way that I cannot think of to lower the impedance.

Yes, I insist on doing this because in my prediction, with the anticipated crossover, the speaker impedance with 4-ohm woofer will easily reach 3-ohm (even lower) at some frequency.

[Jay]

Originally Posted by activexp

Why does the low impedance make them not so useful? Isn't modifying the driver a bit extreme? A bit risky I would have thought. If the mid and tweeter are 8 ohm and the XO designed correctly I can't see any problem with 4 ohm woofers. Unless I'm missing something

Hmmm... may be I'm just paranoid. I don't want the speaker system impedance to be too low. What do you think is the acceptable minimum impedance of current loudspeaker?

[18Hurts]

So wiring the two 4 ohm woofers in series is out?

You would get your 8 ohms and another 3dB of output. The size of the box will go up which might be your issue.

The other option is to take the second woofer and make a bandpass box and stuff it somewhere. Say your woofer crosses at 800Hz, the bandpass box can be tuned for 40 to 80Hz and naturally filter out the other frequencies through the port. Stick it above the ceiling tiles, under furniture or make it a speaker stand.

It would be rather odd but it would work. If you need a speaker stand, it could be made to do that function and also boost the deep bass response while increasing the impedance to 8 ohms.

[activexp]

Originally Posted by Jay

Hmmm... may be I'm just paranoid. I don't want the speaker system impedance to be too low. What do you think is the acceptable minimum impedance of current loudspeaker?

Difficult to say, really depends on the amp. If it's well designed it should be able to handle 4 ohms or less without distress.

[Jay]

Originally Posted by 18Hurts

So wiring the two 4 ohm woofers in series is out?

The other option is to take the second woofer and make a bandpass box and stuff it somewhere. Say your woofer crosses at 800Hz, the bandpass box can be tuned for 40 to 80Hz and naturally filter out the other frequencies through the port. Stick it above the ceiling tiles, under furniture or make it a speaker stand.

I don't understand. How can I bandpass a woofer to 40-80Hz while putting it in series with other woofer bandpassed for 80-800Hz??