horn speaker and normal speaker

[crutschow]

So does a speaker, if there was any need to specualte, it's actually power driven, not voltage or current, but both

You've now gone from the realm of speakers, resistors, motors etc. to active semiconductor devices, there's really no basis for comparing them.

I wasn't speculating. A speaker needs to be driven by a voltage source, not a current source, which is why I referred to it as a voltage operated device. Of course it also takes current (and thus power) but so do virtually all electrical or electronic devices.

I was trying to give a somewhat generic explanation of the difference between a voltage operated and a current operated device with the speaker being one and the LED (which was the first example I though of) being the other. I wasn't comparing them other than to show an example of each type of device.

 

[carbonzit]

I still have no idea what means a "voltage source" or a "current source".

I understand, of course, that there are such things as constant current sources or voltage sources. Is this what is meant by that? If so, why not just call it that ("a speaker needs to be driven by a constant-voltage source", or whatever is the case)?

Isn't this just a needless abstraction? or does it have some fundamental meaning that I'm missing here?

Look, let's say I hand you a black box with two output terminals, and ask you to tell me whether it's a voltage source or a current source. Even assuming you can find the Thevenin or Norton equivalent, how would you determine this? and would it really matter?

 

[Nigel Goodwin]

I still have no idea what means a "voltage source" or a "current source".

I understand, of course, that there are such things as constant current sources or voltage sources. Is this what is meant by that? If so, why not just call it that ("a speaker needs to be driven by a constant-voltage source", or whatever is the case)?

Isn't this just a needless abstraction? or does it have some fundamental meaning that I'm missing here?

I would say it's a 'meaningless abstraction', and probably incorrect as well?.

The LED example is also pretty meaningless, as while an LED 'could' be considered 'current driven', a speaker can't be considered 'voltage driven' as it's no different to a resistor, motor etc.

 

[carbonzit]

Right. I was thinking about probably the clearest example one could think of as what some would consider a "current-driven" device: an ammeter.

True enough, an ammeter, placed in series in a loaded circuit, measures current. But what does it mean to say that it's "current driven"? Obviously, it requires some non-zero voltage to operate; otherwise, the needle wouldn't move (or the little LCD digits wouldn't change).

So why not just say that it is a current-measuring device and leave it at that?

 

[4pyros]

Current and voltage source comparisonMost sources of electrical energy (mains electricity, a battery, ...) are best modeled as voltage sources. Such sources provide constant voltage, which means that as long as the amount of current drawn from the source is within the source's capabilities, its output voltage stays constant. An ideal voltage source provides no energy when it is loaded by an open circuit (i.e. an infinite impedance), but approaches infinite power and current when the load resistance approaches zero (a short circuit). Such a theoretical device would have a zero ohm output impedance in series with the source. A real-world voltage source has a very low, but non-zero output impedance: often much less than 1 ohm.

Conversely, a current source provides a constant current, as long as the load connected to the source terminals has sufficiently low impedance. An ideal current source would provide no energy to a short circuit and approach infinite energy and voltage as the load resistance approaches infinity (an open circuit). An ideal current source has an infinite output impedance in parallel with the source. A real-world current source has a very high, but finite output impedance. In the case of transistor current sources, impedances of a few megohms (at DC) are typical.

An ideal current source cannot be connected to an ideal open circuit because this would create the paradox of running a constant, non-zero current (from the current source) through an element with a defined zero current (the open circuit). Also, a current source should not be connected to another current source if their currents differ but this arrangement is frequently used (e.g., in amplifying stages with dynamic load, CMOS circuits, etc.)

Similarly, an ideal voltage source cannot be connected to an ideal short circuit (R=0), since this would result a similar paradox of finite non zero voltage across an element with defined zero voltage (the short circuit). Also, a voltage source should not be connected to another voltage source if their voltages differ but again this arrangement is frequently used (e.g., in common base and differential amplifying stages).

Contrary, current and voltage sources can be connected to each other without any problems and this technique is widely used in circuitry (e.g., in cascode circuits, differential amplifier stages with common emitter current source, etc.)

Because no ideal sources of either variety exist (all real-world examples have finite and non-zero source impedance), any current source can be considered as a voltage source with the same source impedance and vice versa. These concepts are dealt with by Norton's and Thévenin's theorems.

From Wiki

 

[KeepItSimpleStupid]

Let's add the "plasma speaker" to the mix: https://en.wikipedia.org/wiki/Plasma_speaker

"he air itself is driven directly by expansion of the plasma as the current through it varies."

 

[carbonzit]

Let's add the "plasma speaker" to the mix: https://en.wikipedia.org/wiki/Plasma_speaker

"he air itself is driven directly by expansion of the plasma as the current through it varies."

So what?

As they used to say, "what does that have to do with the price of tea in China?".

 

[crutschow]

I would say it's a 'meaningless abstraction', and probably incorrect as well?.

The LED example is also pretty meaningless, as while an LED 'could' be considered 'current driven', a speaker can't be considered 'voltage driven' as it's no different to a resistor, motor etc.

We seem to be having a semantics issue, so here is my understanding of the definitions:

By voltage source I was referring to a constant voltage source with an ideal output impedance of zero.

By current source I was referring to a constant current source with an ideal output impedance of infinity.

A voltage operated device is one that is designed to operate directly from a voltage source.

A current operated device is one that is designed to operate directly from a current source.

Thus a typical loud speaker or incandescent bulb is a voltage operated device, and an LED or neon bulb is a current operated device.

Now in practice you can operate these devices with less than ideal sources but the source for each type of device should be predominately the appropriate type for proper operation.

If you don't agree with those definitions, that's your prerogative, but I believe they serve as a useful distinction. For example, many of the newbies try to use an LED as a voltage operated device with often catastrophic results (for the LED) when, of course, it needs to be used as a current operated device.

 

[KeepItSimpleStupid]

Fundamentally when you look at Maxwell's equations for magnetic/electric fields: https://en.wikipedia.org/wiki/Magnetic_field the independent variable is current. This, the typical voice-coil loudspeaker is a current controlled device.

The incaadescent light bulb is also a CURRENT controlled device. It is often referred to as a current dependent resistor. Current is the independent variable.

 

[carbonzit]

Thus a typical loud speaker or incandescent bulb is a voltage operated device, and an LED or neon bulb is a current operated device.

Fundamentally when you look at Maxwell's equations for magnetic/electric fields: https://en.wikipedia.org/wiki/Magnetic_field the independent variable is current. This, the typical voice-coil loudspeaker is a current controlled device.

Hmm; reminds me of the old riddle: "You come to a fork in a road and don't know which way to go. There are two people there: one always lies, the other always tells the truth ...".

You know what? I don't care about any of this. It's like arguing over how many angels can dance on the head of a pin. Or semantic fun and games ... and really, what does any of this matter?

 

[KeepItSimpleStupid]

Probably, but similar discussions might in understanding things like inductance.

I've been trying to learn free Solid Edge CAD and I could not grasp a fundamental concept.

You HAVE to pick up the hammer first before you hit the nail rather than pick up the nail and hit with the hammer. No wonder why I was having a hard time because I lacked a fundamental concept that I could not extract from the documentation.

It's like:

Algebraic: a+b,
RPN: a b +
and
LISP: + a B

I never liked LISP

and the operations are not Polymorfic like you might find in C++ or LabVIEW. This application is more like PASCAL.

The above are analogies.

 

[crutschow]

You know what? I don't care about any of this. It's like arguing over how many angels can dance on the head of a pin. Or semantic fun and games ... and really, what does any of this matter?

You know what? If you don't care about this than don't read the posts.

Edit: Reminds me of the old saying: "You can lead a horse to water but you can't make him drink."

In engineering and science, accurate and agreed upon definitions are necessary for the unambiguous exchange of information. If each has his own definition of terms then the exchange becomes babel.

 

[crutschow]

Fundamentally when you look at Maxwell's equations for magnetic/electric fields: https://en.wikipedia.org/wiki/Magnetic_field the independent variable is current. This, the typical voice-coil loudspeaker is a current controlled device.

The incandescent light bulb is also a CURRENT controlled device. It is often referred to as a current dependent resistor. Current is the independent variable.

You are confusing dependent and independent in normal operation of the devices. The independent part is that which does not vary due to changes in the device characteristics. In both these devices, that is normally the voltage.

It's true that the magnetic field from the voice-coil current moves the cone. But the applied independent variable in normal operation is a voltage not a current. The current depends upon the impedance of the speaker, which varies with frequency. It is the dependent variable.

Similarly in normal operation the independent variable when powering an incandescent bulb is the voltage. That's why they are specified for voltage not current. The current is the variable that depends upon the fixed operating voltage and the bulb resistance at its operating point thus it is the dependent variable

 

[ronsimpson]

I still have no idea what means a "voltage source" or a "current source".

An audio amplifier with a gain of 10; with 1 v in you get 10v vout. The 10v does not change if the load is 4 ohms or 8 ohms or 16 ohms or open. The amplifier has feedback to keep the output/input = 10.

A current amplifier; with a gain of 1V/2A will, with 1V in will try to deliver 2A into any load. 4, 8 or 16 ohms makes no difference in current.

Several times I designed equipment where something is moved by electricity. A coil if wire causes something to move. In most cases 0.01% error is too much. For a speaker, the temperature changes, the resistance changed and thus the current changes and the loudness changes. A change of 0.5db is no problem. As the voice coil self heats it causes a low frequency distortion (sub audio) that no one cares about. In the case of scientific equipments 1 degree of temperature causes resistance changes and thus current changes that is not acceptable. By measuring coil current, the amount of movement is controlled even with resistance changes. Under heavy load coils often have 50C of self heating.