KLF-30: Woofers in parallel or series?

[PrestonTom]

Guys,

Are the two K-31 woofers on a KLF-30 wired in series or in parallel.

IOW, If you measure the DCR (with the crossovers disconnected) would it be less than 6 ohm or greater than 6 Ohm? The only spec I can find suggests they are nominally 8 Ohm speakers.

Thanks,

-Tom

Edited February 18, 2016 by PrestonTom

[ClintonH]

The crossover schematic is in the Crossover thread, here it is

 

[WMcD]

I've only seen woofers in parallel. This is because the woofer needs the low output impedance of the amp without the other woofer in series.

You don't have to disconnect the crossover to measure the d.c. resistance at the terminals. You will be adding the dcr of the inductor, but that should be well under 1 ohm.

So I think you'll see 4 ohms or a little less.

WMcD

[PrestonTom]

I've only seen woofers in parallel. This is because the woofer needs the low output impedance of the amp without the other woofer in series.

You don't have to disconnect the crossover to measure the d.c. resistance at the terminals. You will be adding the dcr of the inductor, but that should be well under 1 ohm.

So I think you'll see 4 ohms or a little less.

WMcD

I understand what you are saying. I have seen cases where woofers are wired in series. The benefit, I am guessing, was to present a higher ("easier") impedance to the amp, but the cost was distortion from the first transducer "adding" distortion to the second transducer. 

[WMcD]

I don't think it is a distortion thing.

I have to noodle with the situation a bit more.

We see a high impedance at resonance. That is because the motion of the driver is creating a voltage at the terminals where we are applying voltage from the amp.

We have to look at like two dry cells in parallel, plus to plus and minus to minus. Each battery "sees" a voltage from the other battery and no current flows. And the V/I has a very small denominator. Hence high resistance.

We know that resistance is the ratio of voltage divided by current. It is always a ratio. This is an important idea because in some simplistic thinking, resistance is just a block of carbon. In reality it is that ratio. Like speed is not a thing, it is miles / hours.

So thinking a bit farther. Assume the woofers are in series.

Start with the lower one in the series. The reverse emf (electromotive force is similar to voltage) is high at the plus terminal and low at the negative terminal. But the negative one is at ground because of the low impedance of the amp.

But at the upper one in the series, the reverse emf is driving the negative terminal lower than the upper terminal (all relative). And the upper one is at ground again because of the impedance of the amp.

This gets complicated.

But I think that the junction of the plus in the "lower" woofer and the minus in the "upper" woofer form a virtual ground, which is to say, zero voltage.

In this way, each woofer in the series is trying to dump current into a short circuit. This is the same as a parallel set up or just with a single woofer connected to an amp.

So I was wrong to say that there is some interference. It all balances out.

There are a couple of difficult concepts here.

One is that SS amps have a very low output impendence. That is to say that if a woofer becomes a source of voltage and current, these are developed back across the output of the amp. The amp looks like a low electrical impedance or a short circuit. This is the damping factor. When the woofer becomes a generator or microphone, the amp is a load and when we put a hand cranked generator into a heavy electrical load (zero ohms, it is hard to crank. There is eventually mechanical damping.

The second is "virtual ground." In the circuit analysis we pick something as ground or zero volts. Usually the chassis. But when things are this or that, some other place or junction is forced to zero volts. So it looks like (virtual) that zero volts.

Sorry if this got complicated.

WMcD.

[PrestonTom]

Ahhh, I see there is now a schematic (thanks Clinton). I know the the crossover point is nominally 825Hz and the woofers are about six-ish Ohms. So I can work backwards once I have had my coffee.

Thanks

[pzannucci]

Yes, the crossover thread is indispensable.  Parallel though 

 

If you are looking at crossover changes or how the crossover works in the KLF-30 you will have to work against the inductance and rising impedance at crossover.  That's why many use a zobel network on the woofer (mid also) so you can have more consistent impedance and not have to fight the variation of the driver along with the associated frequency response variations.  Some say zobels rob power and there are extra parts cost which go way up in a multi-driver system so is justified depending on your thought process and target.  I would think once you are at that area of the response where the zobel is needed, you really don't need the power since output should be tapering off.

 

As you notice, those values are no where close to text book for say 6-8 ohms where the woofers are likely at near 825hz.  Enjoy the dial in.

Edited February 19, 2016 by pzannucci

[PrestonTom]

In all likelihood I will wire them in parallel (just like on a Jubilee) and use an electronic crossover. My plan is to mimic a two-way KLF 30 and substitute a K-510 for the mid and tweeter. 

 

This will be used a center channel for music. The room is only 11 ft wide and the L&R Jubilees already take up considerable real estate. Other wise I would use my other Jubilee bass bin. Alas, I will need to find a home for those.