[DerAlte]

Originally Posted by anToNIcHeN

More theory...
P = (2V)^2 / R ==> P = 4 V^2/R
==> P = 4 P0 where P0 is the initial power output...
So there you go.. in theory you get 4 times the power output than from a individual channel.
But like LBM has mentioned but in this world nothing is perfect .

@antoni-mon, definitely nothing is perfect in this world.
* It is Impedance, not resistance, that the power is being pushed through, so R would be too much of a simplification. The L matters more, 'cos R will not provide motive force to the voice coil - it is an incidental physical property which caps the current that CAN flow through the coil when a voltage is applied. The actual current is proportional to d(of something or the other)/dt
* Voltage is double at saturation only, i.e. when the signal is clipping. At other times, it is proportional to the signal, i.e. 0 < amp o/p voltage < supply voltage to final power section. Less than, not 'less than or equal to'
* Power is quoted at a certain distortion level, and is always less than the peak theoretical power capability of the output stage (it ceases to be music at that level)

[santosh.s]

DerAlte, regarding the effect of former, what are you trying to convey?

I was just trying to make it more apparent that the electro-magnetic damping caused by aluminum former may NOT be negligible as compared to that caused by the (shorted) voice coil. I had following in my mind when I said that (presumptions)-

1. former and VC are traversing in the same magnetic field, no difference.
2. their geometries are comparable, one is not negligible as compared to the other in terms of length, diameter, longitudinal cross section (this should include all turns in case of VC).
3. conductivity of aluminum is lesser than copper, but not negligible (this is a fact, I am sure)

Damping is going to be caused by the induced current, which will flow along circular paths perpendicular to the length of the former (just like coil turns). The amount of this current will depend upon the resistance, and I used "current carrying capacity" synonymously as "low resistance". There is no EMF along the length, so whether you consider former as a whole or split into N number of separate rings shouldn't really matter. In case of VC, we have to short two ends because otherwise there won't be any path for induced current to flow since the coil turns are insulated. If the VC didn't have any insulation between its turns, it would be just like another copper former. But note that its damping effect would not change (of course in this case it will be always shorted, no case of being "open"). Now, do you think that damping of aluminum former is "negligible" as compared to the copper "former"?

In fact I was essentially getting at what you said:

The alu former's current capacity is quite large (check longitudinal cross-section area of the former)

If this capacity was negligible as compared to VC, then I would have agreed that it's damping effect too should be negligible. Hopefully, it is clear now (?)

[DerAlte]

Originally Posted by santosh.s

DerAlte, regarding the effect of former, what are you trying to convey?

You have to consider the former as one shorted turn only. If you consider them as separated rings, you are ignoring the fact that such separation automatically assumes insulation between turns, no matter whether air or vacuum separates them.
The electro-magnetic equation is based on (N B v sin ) where:
N = number of turns (insulated from each other; in your example your assumption is incorrect)
B = flux density in lines/area (this is what the shorted VC is being dragged through)
= length of the conductor (length of 1 turn = mean circumference of VC, the larger the better)
v = velocity (here comes the time factor, he he)
= the angle between the conductor and flux field (normally perpendicular)
(No offense meant, Santosh, I am not questioning your knowledge by putting the equation; the exact equations for the VC damping - which are differential equations based on the above - requires a PhD in EE, and I am not)

Originally Posted by santosh.s

I was just trying to make it more apparent that the electro-magnetic damping caused by aluminum former may NOT be negligible as compared to that caused by the (shorted) voice coil

Q.E.D. above!

I had following in my mind when I said that (presumptions)-
1. former and VC are traversing in the same magnetic field, no difference.
Correct.
2. their geometries are comparable, one is not negligible as compared to the other in terms of length, diameter, longitudinal cross section (this should include all turns in case of VC)
Incorrect to generalize 'geometry', since the electro-magnetic equations specify everything precisely
3. conductivity of aluminum is lesser than copper, but not negligible (this is a fact, I am sure)
It is. However, it doesn't play a significant role in the electro-magnetic equation

Originally Posted by santosh.s

There is no EMF along the length, ... compared to the copper "former"?

The damping is by opposing forces, right? The force is dependent on mag field strength generated the shorted VC. And that force is dependent on number of turns, right? Or am I getting something horribly wrong here?

Originally Posted by santosh.s

Hopefully, it is clear now (?)

I sincerely hope so too - I am not perfect, OEO!

[santosh.s]

DerAlte, as clip said in the other thread, it is turning out to be an exercise for brain which has been idle off late...let me try to explain.

The equation mentioned by you gives the EMF, i.e. electro-motive force that gets generated (not to be confused with the mechanical "force", it is a voltage). You are missing one important point- damping is not merely caused by this EMF. There needs to be resulting current for the opposite mechanical force to be produced. The opposite force is nothing but the concerned damping. This implies another point that you are missing- this current obviously depends upon the resistance, so resistance is important. If it was a non-conducting material, the EMF would make no difference at all.

OK, so let us come back to mathematical equation (no I am not going into differential equations...as if I know them). For one turn (N=1):

EMF = B l v sin(theta) = K1 (constant)

Let us say one turn has resistance R, then current is:

I = EMF/R = K1/R

The mechanical opposite force is proportional to this current and the length, so:

F = K2 l/R

That means R=0 is infinite damping, R=infinity is no damping. If there are N such completely independent, insulated turns, the net force simply gets multiplied by N:
Ftotal= K2 N l/R

Now consider a proper VC, where N turns are connected in series and shorted at two ends. So both EMF and the resistance gets multiplied by N. So the equation for current remains unchanged:

I = (N K1) / (N R) = K1 / R

Again the mechanical force is proportional to current and length, with the same proportionality constant as before (rest of the system is unchanged):

Ftotal = K2 N l/R

So, whether we have N separate rings or a single shorted coil, the net result is same. Going one step ahead, if you short (abut) those separate rings together, it is not going to change the behavior. Since there is no voltage along the length of the former or coil, connection or disconnection of equi-potential points do not matter.

[low_bass_makker]

Originally Posted by santosh.s

DerAlte, as clip said in the other thread, it is turning out to be an exercise for brain which has been idle off late...let me try to explain.

So, whether we have N separate rings or a single shorted coil, the net result is same. Going one step ahead, if you short (abut) those separate rings together, it is not going to change the behavior. Since there is no voltage along the length of the former or coil, connection or disconnection of equi-potential points do not matter.

Correct. more the brain does the exercise it is improved more...

About the Voltage across the VC. if there is no voltage across it how does it get to function. I am trying to say that if there is no voltage then there will be no EMF generated then how does the VC moves...

[DerAlte]

There needs to be resulting current for the opposite mechanical force to be produced. The opposite force is nothing but the concerned damping.
Correct.
This implies another point that you are missing- this current obviously depends upon the resistance, so resistance is important. If it was a non-conducting material, the EMF would make no difference at all.
OK, so let us come back to mathematical equation (no I am not going into differential equations...as if I know them). For one turn (N=1):
EMF = B l v sin(theta) = K1 (constant)
Let us say one turn has resistance R, then current is:
I = EMF/R = K1/R
Thamba! Here current is not static as in DC circuits, it is dynamic - no movement of VC, no current. So both EMF and current are time-dependent. That is why the differential equation.
Simplified, d(EMF)/dt = dI/dt*(coil impedance). Current is produced by the coil moving in the mag field, which produces and EMF across the L and R of the coil. When the coil is shorted, the EMF is a notional entity. L is proportional to Nturns. Higher the turns, more the EMF - can produce a spark, but not much power unless the conductor is thick - less R, more I, more P.

Tchah, and that is where the clue is - this (coil-based damping) is a technique used for long in instrumentation (remember galvanometers? seismometers?). And even I made a fundamental mistake - the damping is by ENERGY DISSIPATION (taking away energy from the moving SYSTEM), not mechanical opposition. Shorted coil takes away mechanical energy and dissipates it as heat energy by way of the electrics. Fine as long as there is adequate ventilation.

More turns, more R, more Pdiss (R*I^2). Bell curve:
- too much R, too less I to matter
- too less R, too less power to matter.
Shorted coil is within bell curve middle. Alu former is the second case, and WILL produce damping - but in the higher frequency range where dI/dt is higher due higher acceleration of the VC system.

Does my rambling make any sense, OEO?

I can visualize a sagely *raising of eyebrows and closing of eyes, with an enigmatic smile* by Navin: q.v. Driver conversions and Re: Shiva Wiring Question

[navin]

Originally Posted by DerAlte

I can visualize a sagely *raising of eyebrows and closing of eyes, with an enigmatic smile* by Navin: q.v. Driver conversions and Re: Shiva Wiring Question

Just I was wondering about jumping in. Der Alte and Santosh were really having fun there for a while. :-)

Dan Wiggins is an excellent engineer and allround person. I suggest that you study hsi work. Mike Dzurko (who built my DV12s) is more reticient.

[hydrashok]

Good god! This thread reads like a mad scientist's convention!

I think now TBHP needs an Uber-tech ICE section fenced away from normal folks (like me) where you folks can be locked in (and the key thrown away )!

Disclaimer: Guys you know I'm joking, right? I don't want to offend anybody by mistake. Though 99.99% of all this goes over my simple head, it is really nice to see more mature ICE talk here. I wouldn't see any of this anywhere else

[DerAlte]

Originally Posted by navin

Mike Dzurko (who built my DV12s) is more reticient.

OK, let's hear about it

[anToNIcHeN]

Originally Posted by Lifewater

Situation is such that I can neither change the amp nor the sub. The sub installation manual says "NEVER connect only one voice coil of the subwoofer. The product may be irrrepairably damaged" the amp manual says "In bridged mode ensure the minimum impedence is not less that 4ohms. otherwise the product may be damaged". Looked around the threads in this context but could not decide what connection to use. Some says - series mode (Amp runs cooler) some says --One voice coil(bur the sub manual says otherwise) some says- individual coils to individual channels(some advice against it). Oh lord what to do????

Originally Posted by Sam Kapasi

4 different opinions!! Ha, if I was a newbie I'd have burst into tears!

"Oh Lord what to do???.... I asked a simple question and look at what I got!"...
hahahaha.... I am just thinking what this poor soul is going thru right now!..

[navin]

Originally Posted by DerAlte

OK, let's hear about it

It was 1994 or something when we did that. The DV12 is the precursor of teh SV12 used in the Titan sub. Mike built a limited number of DV12 (dual ring magnets, huge motor, reasonable Xmax, resoanable Mms, etc..) for DIY sale at $95 each. I was a lucky one and got 6. I gifted 2 to a friend (I also gave the same friend my JBL 2245 woofers) and kept 4.

[santosh.s]

Originally Posted by DerAlte

Thamba! Here current is not static as in DC circuits, it is dynamic - no movement of VC, no current. So both EMF and current are time-dependent. That is why the differential equation.
Simplified, d(EMF)/dt = dI/dt*(coil impedance). Current is produced by the coil moving in the mag field, which produces and EMF across the L and R of the coil.

Well, I was trying to avoid differential equations as promised. I assumed "v" to be constant in the "illustration". That doesn't mean VC is not moving. If it is stationary, then anyway v=0! For understanding purpose, you can think of it as a "point" in time where a particular value of v is applicable, and the coil obviously moves only by distance "delta-x" which is by definition described as "infinitesimally close to, but not equal to zero". An other option is to assume that the coil is really moving with a constant v, which also means that you have to assume that the driver has unlimited Xmax! (next version of XBL^2 => XBL^infinity)

- the damping is by ENERGY DISSIPATION (taking away energy from the moving SYSTEM), not mechanical opposition. Shorted coil takes away mechanical energy and dissipates it as heat energy by way of the electrics.

Yes, "energy dissipation" is the standard definition of damping. But if you analyze it carefully, dissipated energy and the opposing force are closely related, they are just two sides of the coin.

OK, what is dissipation?.... Energy can neither be created nor destroyed, so dissipation= conversion into heat. But then how would you define dissipation if you were talking about a system whose purpose is to produce heat (say a geyser)? I guess if it creates some sound pollution, then that should be called it's dissipation...exactly opposite, you see!

So what is getting "dissipated"?...coil's motion is getting dissipated as heat. We don't want it to move by itself, i.e. it should stop as quickly as possible once the amp's signal becomes zero or when amp is feeding some signal, it should strictly follow the command without deviating. Basically the opposite force that I was talking about actually stops its motion by indirectly converting it into heat. The point is that the work done by that opposite force must be the same as heat dissipated (and you should be able to believe this even without looking into equations, right?). That is nothing but what we are calling damping. How good the coil is at that depends upon how fast it can do it.

Let us tally, by calculating how fast the heat is dissipated (i.e. power) instead of the mechanical force. Please stick to the assumption that I made, it should be enough for understanding purpose, and my previous simple equations can be reused.

Power dissipated in one single turn or a ring:
= I^2 * R
= (K1/R)^2 * R
= K1^2 / R
= K1' /R (K1' => another constant)

Power dissipated in N separate rings:
= K1' * N/R

Power in case of whole coil with N turns:
= (K1/R)^2 * NR
= K1' * N/R

The bottom line is that it is proportional to N/R in both cases with same constant of proportionality. They are providing same power dissipation, so same amount of damping.

We can even tally with the mechanical power also, you have to just multiply Ftotal by v. So if v is same, mechanical power in both cases is also same. In fact if one resolves K2, it should be exactly equal to the electrical power dissipation

More turns, more R, more Pdiss (R*I^2). Bell curve:
.....
.....
Does my rambling make any sense, OEO?

No..no... this is completely wrong. Before drawing any conclusion about how R affects the equation, you must be sure that I is independent of it, when rest of the system doesn't change. But in this case, I is dependent on R, EMF is not. So, you should use the equation EMF^2 / R instead of above. You are saying open circuit will dissipate maximum heat whereas a short will not dissipate anything at all? That would have been true for a given current, but it is exactly opposite for a give voltae!!

[santosh.s]

Originally Posted by low_bass_makker

About the Voltage across the VC. if there is no voltage across it how does it get to function. I am trying to say that if there is no voltage then there will be no EMF generated then how does the VC moves...

We are trying to understand how the moving VC stops... so how it got into motion is not important, you can just tap it for testing purpose!

(Hope I got your question right...otherwise sorry )

[low_bass_makker]

Ever tried this.

First take a sub and push the diapram with a hand. It will feel like you are only opposing the suspension of the sub.

Now try this. short the speaker treminal and now press it again. if you press it slowly you would not feel the differnce. but if you press it fast you will feel a very strong force which is opposing it. That is the EMF generated.

Try it ...

the power to stop the VC of the driver will also depend on the amp connected to it. when the signal from the amp is stopped the sub should stop but it is very difficult to have this type of stuff in the real world. without going in to details of equations as it make other member scare...I would suggest to stick to little of plain english.ok when the amp opposes the back current genrated by the sub the sub VC gets hot. also when the sub is getting loads of power it also get hot. And I have fried number of speaker with this.

Yaar there are hell of lot parameter

[santosh.s]

Completely agree, LBM.
If you compare the speaker to car, then amp is like the engine. Playing and damping is like accelerating and engine-braking!