Speakers need current to operate right ?

I mean, if you have an output stage with very low current, but very high voltage, both under and over the requirements respectively, will the speaker work ?

The magnetic coil in the speaker actually needs current rather than voltage in order to create the flux required to move it. So if your output stage has very small currents, BUT very high voltage, that's a failure right ?

So therefore, what's the purpose of power amplifiers in speaker circuits? If all you need is a high current, why is power amplified anyways?

 

Essentially a loudspeaker coil is an Inductor, that alters its impeadance with the frequency of the audio signal, it needs Voltage to move it in/out, but Current is also needed for total movement of the coil continously over its frequency spectrum, that is why they are designed in Wattage rating.

 

Speakers need current to operate right ?
I mean, if you have an output stage with very low current, but very high voltage, both under and over the requirements respectively, will the speaker work ?

At conditions you mentioned electrostatic loudspeaker will work very good. https://en.wikipedia.org/wiki/Electrostatic_loudspeaker
For example voltage is 1000 V, current is 10 mA. Then power is 1000 * 0.01 = 10 W.
Dynamic speaker with coil resistance = 4 Ohm needs 6.3 V for output power 10 W. In this case current will be 1.575 A.
https://en.wikipedia.org/wiki/Loudspeaker
In both cases we will have same loudness.

 

So is the ohms given in the dynamic speaker actually the impedance of the inductor? I thought it was the resistance of the wire....

 

So is the ohms given in the dynamic speaker actually the impedance of the inductor? I thought it was the resistance of the wire....

It's a combination of the speaker coil resistance, and the back EMF generated by the motion of the speaker coil through the magnetic field.
It's the power absorbed by the current times this back EMF which is converted to mechanical power that does the work when the speaker is generating a sound.
The rest of the power is absorbed as I²R losses in the coil resistance.
It's similar to the way an AC motor takes power from the input to turn the shaft and generates back EMF in the process.

The DC resistance of a speaker is generally always less than it's ohm rating.

 

So is the ohms given in the dynamic speaker actually the impedance of the inductor? I thought it was the resistance of the wire....

Impedance depends on freguency:

 

It's a combination of the speaker coil resistance, and the back EMF generated by the motion of the speaker coil through the magnetic field.
It's the power absorbed by the current times this back EMF which is converted to mechanical power that does the work when the speaker is generating a sound.
The rest of the power is absorbed as I²R losses in the coil resistance.
It's similar to the way an AC motor takes power from the input to turn the shaft and generates back EMF in the process.

The DC resistance of a speaker is generally always less than it's ohm rating.

Crustachow, I need to have a word with you. Are you available?

Can you clarifity this to me please? I think you and AnalogKid are the best in this forum so I only take your replies into consideration here. For example replies by people like OBWD67583 are worthless.

 

I understand there is impedance in the speakers and hence we need voltage in order to push against this impedance, however........Why dont we just increase the current then? Why power?

Power is V x I.
To increase the current through the speaker impedance you need to increase the voltage which, by definition, increases the power.
It's power that does the work, not current all by itself.

So the speaker has a frequency dependent Z, so when we amplifiy power, we automatically amplify both voltage and current

That's basically it.
The amplifier has a very low impedance output (meaning the output voltage does not change significantly for a varying load output current).
It generates a voltage which is an accurately (for a good amp) amplified version of its input voltage from your audio source.
The current then is determined be speaker impedance for the frequencies of the audio signal.
From the speaker impedance graph in post #6 you can see that for a given voltage, the current will vary will the frequency (V/Z), but that's okay since a speaker is designed to give an accurate acoustic output for the voltage input, not the current.
Thus the speaker input power can vary with frequency for a given input voltage.
This basically means the speaker efficiency (acoustic output power versus input power) varies with frequency such that the acoustic output power is essentially constant for this variation in input power (at different frequencies).

Make sense?

 

Ask yourself this. How much current can you push through a speaker coil with no voltage? Ask yourself what is the difference between a speaker coil and a solenoid? Will a solenoid have a current passed through it with no voltage applied? (ignoring all forms of superconductance, please, I am discussing normal speakers/solenoids).
If you find that a voltage is needed to push a current through a coil (any coil) what would be the power dissipated in the coil?
Simple experiment. Get a speaker(old one preferably) connect a battery to the speaker and observe the speaker cone motion(do it quick or you may burn out the coil or you can use a suitable resistor in series). Now reverse the connections and observe the speaker cone.
If you have the equipment measure the current and volts of the speaker coil. Can you get current to flow with no volts? How much power is the speaker dissipating from your battery?

 

Voltage is difference of potentials of electric circuit.
Current is the movement of electrons under the action of voltage.
Since electrons in free form locate in wires, resistors, semiconductors and so on, therefore current is the result of voltage. Current and voltage must not view apart.

For example voltage is 1000 V, current is 10 mA. Then power is 1000 * 0.01 = 10 W

In this case internal resistance of power supply is 99 996 Ohm + 4 Ohm of loudspeaker. And therefore power for loudspeaker is 0,0004 watt. Extremely loud
But total power is 10 watt, you are right.
PS Sorry for my english

 

In this case internal resistance of power supply is 99 996 Ohm + 4 Ohm of loudspeaker. And therefore power for loudspeaker is 0,0004 watt. Extremely loud

Yes, it is. It will be "Extremely loud" because of electrostatic loudspeaker.
"Electrostatic loudspeakers use high voltages to operate. They need a DC bias of up to 5000 V and use AC voltages up to 5000 V"
http://amasci.com/esloud/eslhwto.html

At conditions you mentioned electrostatic loudspeaker will work very good. https://en.wikipedia.org/wiki/Electrostatic_loudspeaker
For example voltage is 1000 V, current is 10 mA. Then power is 1000 * 0.01 = 10 W.

 

Speakers need current to operate right ?

Yes, and electrons needs voltage to make them move. Semantically, there is no such thing as "current flow". Electron flow = current.

I mean, if you have an output stage with very low current, but very high voltage, both under and over the requirements respectively, will the speaker work ?

It will make sounds, but not very loudly.

The magnetic coil in the speaker actually needs current rather than voltage in order to create the flux required to move it. So if your output stage has very small currents, BUT very high voltage, that's a failure right ?

You misunderstand the relationship between voltage and current. They are not two separate things, but two of the three core aspects of electrodynamics (the third is impedance. The three are completely interrelated. In the classic water analogy, voltage = pressure and electrons equal drops of water. Another term for voltage is potential difference, sorta like the altitude difference between the top and bottom of a waterfall.

So therefore, what's the purpose of power amplifiers in speaker circuits? If all you need is a high current, why is power amplified anyways?

Because what good is a power amplifier that can make 100 amps but at only 1 V, when driving an 8 ohm speaker? Run the numbers.

Voltage times current equals power. A phono cartridge output is around 5 mV into 47 K ohms, for a source power of approximately 53 nW (nanowatts). After the preamp gain (typically 100), the input impedance of the tone controls might be around 10 K; now the signal power is around 25 uW (microwatts). A power amplifier does just that - it increases the signal power into whatever the load is. To make 10 W into a 2 ohm car speaker, you need a circuit that can produce 4.5 V and 2.3 A (both RMS). Therefore the amp has a voltage gain of 9 and a current gain of 46,000. Rerun the numbers for a 32 ohm headphone speaker and the voltage and current numbers will be very different for the same 10 W output.

The normal power amp design flow is to determine the speaker impedance you want to drive and the power level, then solve for the required peak voltage and current values. If you are working with existing parts, then the available voltage and current will tell you the max power available, and combining those with the speaker impedance will tell you how much of that power can be turned into real audio.

ak