Question about impedance!

[eduardokbb]

Sorry for such a dumb question, but these days I was wondering about that.. If I have a real 4 ohms loudspeaker, It'll be more difficult to feed him power, when compared to a real 8ohms speaker. I mean, it's easy for an amplifier to output 8ohms loads, but it's harder to output 4 ohms load.
Nowadays, it's really hard to find an amplifier that can power a trully 1ohm loudspeaker (perhaps that's the reason I think 1ohm loudspeakers aren't produced anymore[I guess]). Assuming what I said is right, the lower the impedance, the harder to drive the speakers.
In another scenario, going from loudspeakers to headphones, we'll find that the most common impedance of a headphone is 32ohms (I guess). It's really easy to find an amplifier capable of amplifying a 32ohms headphone, most smartphones, soundcards can do that. If we try to use the same amplifier to power a 600ohms headphone, we'll notice that it just doesn't work. We'll need something more robust.
The question is: Why in loudspeakers the lower the speaker impedance, the harder to power it and when it comes do headphones, the higher the impedance, the harder to power it? To me, it seems like something at least contradictory, but I'm really sure I'm missing lots of physic concepts that can explain that.

Peace,
Eduardo Barth.

 

[TLS Guy]

Sorry for such a dumb question, but these days I was wondering about that.. If I have a real 4 ohms loudspeaker, It'll be more difficult to feed him power, when compared to a real 8ohms speaker. I mean, it's easy for an amplifier to output 8ohms loads, but it's harder to output 4 ohms load.
Nowadays, it's really hard to find an amplifier that can power a trully 1ohm loudspeaker (perhaps that's the reason I think 1ohm loudspeakers aren't produced anymore[I guess]). Assuming what I said is right, the lower the impedance, the harder to drive the speakers.
In another scenario, going from loudspeakers to headphones, we'll find that the most common impedance of a headphone is 32ohms (I guess). It's really easy to find an amplifier capable of amplifying a 32ohms headphone, most smartphones, soundcards can do that. If we try to use the same amplifier to power a 600ohms headphone, we'll notice that it just doesn't work. We'll need something more robust.
The question is: Why in loudspeakers the lower the speaker impedance, the harder to power it and when it comes do headphones, the higher the impedance, the harder to power it? To me, it seems like something at least contradictory, but I'm really sure I'm missing lots of physic concepts that can explain that.

Peace,
Eduardo Barth.

It is quite simple really.

Ohms law states voltage of a circuit = the current X the resistance.

So if you halve the resistance and keep the voltage the same, the current will double.

If you double the resistance then you need twice the voltage for the same current.

Now the power in the circuit can be expressed as the square of the voltage divided by the resistance, or the square of the current X the resistance.

Now every output device has an internal resistance. So the power dissipated in the device is heat. So the heat in the output device goes up by the square of the current. Now it is heat that destroys devices. So as you lower the resistance the current goes up and you need more robust, larger devices and a beefier power supply.

Now the maximum power into a load is voltage limited. So you need a higher voltage to get the same power into a larger resistance.

So to drive the same power into a 600 ohm impedance takes a much higher voltage than for a 32 ohm impedance.

Now the voltage into the load can never exceed the voltage to the device. For a battery powered device, without an inverter, the voltage to the load can not exceed the battery voltage. So the portable device is voltage limited when driving the 600 ohm load.

Most amps will be severely current limited trying to power a 1 ohm load. For that matter cheaper receivers have trouble with four ohm loads.

 

[cpp]

Some info

http://www.audioholics.com/loudspeaker-design/understanding-impedance-electrical-phase

Loudspeaker Sensitivity & Impedance Explained | Audioholics

 

[eduardokbb]

Thanks for the information.

 

[PENG]

The question is: Why in loudspeakers the lower the speaker impedance, the harder to power it and when it comes do headphones, the higher the impedance, the harder to power it? To me, it seems like something at least contradictory, but I'm really sure I'm missing lots of physic concepts that can explain that.

Peace,
Eduardo Barth.

The question is not quite right. Even for loudspeakers, it is hard to power high impedance speakers. You don't find too many 16 ohm speakers, let alone 32 ohm and 600 ohm ones. There is nothing contradictory here.

 

[eduardokbb]

The question is not quite right. Even for loudspeakers, it is hard to power high impedance speakers. You don't find too many 16 ohm speakers, let alone 32 ohm and 600 ohm ones. There is nothing contradictory here.

Well, I think that a 16ohms loudspeaker is really easy to be driven. Perhaps it needs more raw power to be driven louder, but a week amplifier would run lots cooler running this 16 ohm loudspeaker than running a 1 ohm loudspeaker.
Correct me if I'm wrong.

 

[GranteedEV]

Well, I think that a 16ohms loudspeaker is really easy to be driven. Perhaps it needs more raw power to be driven louder, but a week amplifier would run lots cooler running this 16 ohm loudspeaker than running a 1 ohm loudspeaker.
Correct me if I'm wrong.

You cannot look at "impedance" independant of sensitivity nor can you ever expect flat impedance from dynamic drivers. Most loudspeakers can have 32 ohm peaks at resonance where efficiency is maximal. Solid state amplifiers tend to behave best in this region while some tube amplifiers may lose damping. But simply raising resistance will net you a drop in sensitivity. No point having a nominal 16 ohm speaker if you need to drive twice the voltage to observe the same current draw. End of the day loudspeaker designers are willing to live with 4 ohm speakers as they chase other design goals. The amplifier is rarely the weakest link in most decent systems.