Compound Isobarik, Drivers in series vs //

[pheonix358]

Hi all,

I am designing a speaker at present. It will have 8 Morel MW267 NeoLin drivers in compound isobarik mode, ie 4 pairs.

I would like some advise as to the difference between series connection within the isobarik pairs. This then allows the pairs to be 16 Ohm and the four pairs in // come down to 4 Ohms. Efficiency gain is 6 dB over a single driver (90 dB)

What is confusing me is the action of back emf in relation to the out of phase connection.

Any help appreciated.

Yes, I will describe the speaker project when I have a firmer idea. Other drivers are 4 MW144 and a modified (by Morel) MDT33.

Oh, all the above refers to one mono speaker. Double it all for stereo.

[pheonix358]

Hi again,

The best I came up with was that since back emf is created by vc motion and since each voice coil is moving in opposit directions any back emf produced would cancel out quite well.

Any other opinions?

[pheonix358]

Musing some more.

First we should understand how back EMF (B/EMF) is generated.

The voice coil moves in and out in response to the applied electrical signal that comes from the amplifier.
This voice coil in motion then interacts with the magnetic field it is moving through generating voltage which is overlaid onto the voice coil.

As I understand it, the amplifier damp this extra energy, this is represented as the Amplifiers damping factor.

If we take two woofers in parallel.

Both woofers produce B/EMFand the amplifier sees all of this energy and dampens it.

If we take two woofers in series.

Both woofers produce B/EMF but the amplifier only sees half of the total energy. The other half of the energy is created on the other side of the voice coil that is connected to the other voice coil. This is what ends up as audible distortion.

If we take series woofers run out of phase

Both woofers create B/EMF but this time each voice coil is moving in oposite directions and thus having an inverse relationship. The amplifier will see half of the the energy generated, but the oposing voice coils will see nothing since it cancels out. (assuming close tolerance of the drivers. These are Morels so that won't be a problem.)

Hm, that should sound, well, it shouldn't sound at all!

[john k...]

When in series the back EMF from all the VC add. When in series the DC resistance of the drivers also adds. As a result the current resulting from the back EMF remains unchanged and the system damping remains unchanged (provided the output impedance of the amp is small compared to the DC R of the drivers).

The only thing that changes in a seriers connection when there is a phase reversal of one driver is that the even order distortion componentes in the back EMF cancel.

[pheonix358]

Originally posted by john k...
When in series the back EMF from all the VC add. When in series the DC resistance of the drivers also adds. As a result the current resulting from the back EMF remains unchanged and the system damping remains unchanged (provided the output impedance of the amp is small compared to the DC R of the drivers).

The only thing that changes in a seriers connection when there is a phase reversal of one driver is that the even order distortion componentes in the back EMF cancel.

Hi John, I don't think it is that simple. When in series, the amplifier does not easily see all this voltage because the voice coils get in the way.

Terry

[pheonix358]

To further explain, think of the attached and work out what happens to the B/EMF generated at B and C. Before it can be damped by the amplifier it has to go through the voice coil and this must add artifacts to the signal from the amplifier. Otherwise, where else does it go?

[john k...]

Originally posted by pheonix358




Hi John, I don't think it is that simple. When in series, the amplifier does not easily see all this voltage because the voice coils get in the way.

Terry

It is that simple. Apply Kirchhoff's voltage law.

[LineArrayNut]

Series phobia is just that. I've read plenty of rumours, but never a definitive, rigorous and peer reviewed analysis. The electrons are not really electrons and they don't "move through the wires". Quantum mechanics negates this phobia quite nicely.

[pheonix358]

In a series connection B/EMF is created and this half this energy is created between the two voice coils. This energy must go somewhere, doesn't just disappear. To get to the amp so it can be damped it must go via the voice coils. Perhaps opening your mind to the possibilities ..... no, may I suggest you look from the reverse, ie try to prove it does make a difference. You may be surprised how often you can gain more insights. Otherwise I am more than happy to simply agree to disagree. With the amount of research I have done lately I am now starting to believe that it can make a difference.

[john k...]

Originally posted by pheonix358
In a series connection B/EMF is created and this half this energy is created between the two voice coils. This energy must go somewhere, doesn't just disappear. To get to the amp so it can be damped it must go via the voice coils. Perhaps opening your mind to the possibilities ..... no, may I suggest you look from the reverse, ie try to prove it does make a difference. You may be surprised how often you can gain more insights. Otherwise I am more than happy to simply agree to disagree. With the amount of research I have done lately I am now starting to believe that it can make a difference.

Apply Kirchhoff's voltage law.