Changing the Impedance on a driver?

[Shawn_K]

I would like to wire three Midrange/Midbass drivers in Parallel but still have a nominal 4 ohm impedance. If I wire three 8 ohm driver in parallel you get 2.66 ohms. I would like to change the impedance to 12 ohms then I can get 4 ohms with three drivers in parallel. The only way I can think of doing this would be to replace the voice coil with one with thinner wire. I don't know if its possible to replace a driver voice coil without destroying the rest of it. I would be making this modification to a either a Dayton Audio RS125P or Tang Band W4-2142 both have aluminum phase plugs. I would like to keep the existing cone, spider and surround. I'm thinking that I either wind the new voice coil myself or have it made by a company that makes voice coils. As an added bonus the new coil former could be made of Titanium with the lead wires 180 degrees apart. Is this a pipe dream? I'm thinking I could attempt the modification on a cheap driver first to get my feet wet.
Shawn

[Æ]

More than likely if you attempt to modify the drivers, you'll ruin them. You might consider having the voice coils replaced professionally. You could always add a couple of ohms of resistance in series with each driver then parallel the whole bunch. Maybe better yet would be to use four drivers, two by two series/parallel.

[Wolf]

You could use a large value small gauge coil for the low-pass as well, and bring up the impedance.

Later,
Wolf

[billfitzmaurice]

I don't know if its possible to replace a driver voice coil without destroying the rest of it.

It isn't. The voice coil, spider, cone and surround are replaced as a unit. Use four 4 ohm drivers.

[Shawn_K]

Thanks for the feedback - It sounds like changing the impedance of a driver is impossible to nearly impossible. Now I really want to do it; because they said "it couldn't be done".

P.S. Now I just need to be brave enough to hack up a nice new driver.

Thanks,
Shawn

[billfitzmaurice]

Thanks for the feedback - It sounds like changing the impedance of a driver is impossible to nearly impossible. Now I really want to do it; because they said "it couldn't be done".

Before you do view a youtube video on driver re-coning. It will be immediately apparent why you can't swap out a voice coil alone.
When 'they' say it can't be done there's usually a good reason why.

[make_some_noise]

You could wire them up for 2.66 ohms and use a series resistor before the crossover circuit to get the impedance back up to 4 ohms. Designers play these sorts of tricks all the time. While you might be able to replace the coil, your chances to get it straight so it travels linear is very low, not to mention it will not sound anything like the original and will have completely different t/s parameters. Really you should just compensate in your crossover and call it a day.

[mzisserson]

You could wire them up for 2.66 ohms and use a series resistor before the crossover circuit to get the impedance back up to 4 ohms. Designers play these sorts of tricks all the time. While you might be able to replace the coil, your chances to get it straight so it travels linear is very low, not to mention it will not sound anything like the original and will have completely different t/s parameters. Really you should just compensate in your crossover and call it a day.

Along this line I did this in the "Iron Cyborgs". I wired 3 2" fullrange speakers in parallel which created a very high effeiency, the large resistance needed to bring them back down raised the Z from a nominal 2.5 ish ohms to almost 6. Granted these are woofers, but if you can give up a little and use a big resistor, you can likely get the Z friendly across the entire band using a high wattage resistor.

[Face]

You could use a large value small gauge coil for the low-pass as well, and bring up the impedance.

Later,
Wolf

IMO, this is your best solution. If these drivers are to be used as woofers, I would NOT recommend a series resistor.

[mzisserson]

IMO, this is your best solution. If these drivers are to be used as woofers, I would NOT recommend a series resistor.

Why not?

A high DCR of a small wire gauge will have more non-lineraity, saturate qucker, and have a host of other potental ill effects.

My application was high passed, so I did not deal with the challanges in a woofer, but I have never seen conclusive evidence, other than its effect of efeciency, for using a series resistor with woofers.

My final thought is any effect the resistor would have is easily predictable and able to be simulated. The expense isnt really a deterrant either since the 50watt, non inductive 1% vishay resistors are available for about $5.

[make_some_noise]

IMO, this is your best solution. If these drivers are to be used as woofers, I would NOT recommend a series resistor.

He said midrange/midbass. I would also assume that using three of these drivers would be for mid usage as it's only a 5" driver and it's a wideband. It makes me think of something like this: http://ca.jbl.com/product-detail-new-jbl/loft-50.html , when dealing with 3 mids.

If you want bass, there is much better options than (3) 5" drivers. Dual 8" drivers will cost less and put out more bass, let alone a proper 10-15" driver.

At the same time a high DCR coil is just a resistor, yet it's has more variables to deal with.

[Shawn_K]

My idea is to use the three drivers in the 150-1500 Hz range in a sealed box critically damped to 0.5 Q and an F3 around 150 Hz. Three drivers with 50-60cm Sd each will provide me 150-180 Sd total, which is equal to a 6.5 inch driver; but I get better dispersion with the smaller drivers. I also plan to space them out a little bit on the front baffle to counter some of the midbass lower midrange floor bounce effect. The bass will most likely be produced with a side mounted 10 inch powered subwoofer.
Shawn

[Face]

You're going to have some serious lobing and phase issues in that configuration. Two under the tweeter or in MTM configuration would be more ideal.

[Face]

At the same time a high DCR coil is just a resistor, yet it's has more variables to deal with.

But a coil is less of a fire hazard.

[monkish54]

I believe the trepidation some are feeling with regards to series resistance on a woofer, is the fact that it increases the driver's Qts...

Face, you have a PM.