Trying to understand impedance

[JustAnAudioLover]

Hi there!

I'm currently having a hard time understanding how impedance works in audio products.

AFAIK, electric impedance is defined by how much "resistance" a circuit has when transmitting electricity. So, the higher impedance, the harder for electricity to "go through" that circuit / cable / product, right?

This seems pretty logical when you look at forums and reviews where people always tell that 300 Ohms headphones are "harder to drive" than, say, 16 Ohms headphones.

But, when it comes to speakers, I always read the opposite: that 4 Ohms speakers are harder to drive than 8 Ohms speakers, despite having a lower impedance. Why is that?

Especially when some people recommend to NOT plug 4 Ohm speakers into 8 Ohm amplifiers to avoid damages, but the opposite seems fine. But on the other side, you can plug 300 Ohms headphones on a smartphone output without any problem - you may not get a great sound, but it won't damage the headphones, right? And the opposite is true too - you can plug 16 Ohms IEMs on a tube amp designed for 300 Ohms headphones, which will have a high output impedance, and yes you'll hear some hiss (elevated noise floor) but no damage to the IEMs themselves.

So, is everything I described here correct, and if so, why is "driving complexity based on resistance" inverted for headphones vs speakers?

Thanks a lot for your explanations

 

[sergeauckland]

4 ohm loudspeakers draw twice as much current as 8 ohm loudspeakers for the same voltage from the amplifier. In that respect indeed they offer less resistance, so are easier to drive...unless you're an amplifier. Amplifiers are designed to provide a fixed voltage output i.e. have zero internal resistance. This is well maintained until the amp runs out of current capacity. An amplifier designed for 8 ohms will struggle more driving 4 ohms as it's being asked to provide twice the current. In that respect, the amplifier sees the loudspeakers as harder to drive. Typically, amplifiers driving 4 ohms will distort more than when driving 8 ohms (although the difference should be small) and will heat up more, so overall, the amp has a harder life driving 4 ohms than when driving 8 ohms.

S.

 

[SIY]

This seems pretty logical when you look at forums and reviews where people always tell that 300 Ohms headphones are "harder to drive" than, say, 16 Ohms headphones.

But that's not even vaguely true. Yes, the impedance (which is complex resistance, if you want to get geeky about it, and is simply the ratio between voltage and current) is higher, but the reason for that is in the motor part of the headphone mechanics, which will probably have more turns of wire on the voice coil which increases the motor force. So, paribus cetaris, it will take more voltage but less current to achieve the same SPL with 300 ohms compared to 16 ohms.

 

[ZolaIII]

 

[JustAnAudioLover]

4 ohm loudspeakers draw twice as much current as 8 ohm loudspeakers for the same voltage from the amplifier. In that respect indeed they offer less resistance, so are easier to drive...unless you're an amplifier. Amplifiers are designed to provide a fixed voltage output i.e. have zero internal resistance. This is well maintained until the amp runs out of current capacity. An amplifier designed for 8 ohms will struggle more driving 4 ohms as it's being asked to provide twice the current. In that respect, the amplifier sees the loudspeakers as harder to drive. Typically, amplifiers driving 4 ohms will distort more than when driving 8 ohms (although the difference should be small) and will heat up more, so overall, the amp has a harder life driving 4 ohms than when driving 8 ohms.

S.

Yeah I got that part right, but why does it seem to be the other way when it comes to headphones? Why amplifiers designed for 300 Ohms headphones aren't going to be damaged when driving 16 Ohms IEMs for instance?

 

[SIY]

Yeah I got that part right, but why does it seem to be the other way when it comes to headphones? Why amplifiers designed for 300 Ohms headphones aren't going to be damaged when driving 16 Ohms IEMs for instance?

They may be unhappy with the low impedance load (or maybe not, the reviews here will tell you). The lower impedance load will draw more current which the device may or may not have been designed to provide.

Think of the extreme case: zero ohms, a short. Will the amp be happy trying to drive that?

 

[JustAnAudioLover]

They may be unhappy with the low impedance load (or maybe not, the reviews here will tell you). The lower impedance load will draw more current which the device may or may not have been designed to provide.

Think of the extreme case: zero ohms, a short. Will the amp be happy trying to drive that?

Oh so it's just that it's not proportional, a.k.a. going from 300 Ohms to 16 Ohms will not multiply the current as much as going from 8 Ohms to 4 Ohms. Is that correct?

 

[digitalfrost]

In terms of driving anything regarding the impedance, think of it like fighters. If I try to push you, and you avoid me completely or simply step back, all that energy that I put into the push will go nowhere. It doesn't really matter how strong I am or how much speed I built up, if there is nothing to drive into, eventually I'm gonna run out of juice.
If you are unaware of me trying pushing you, I can exert most of my force into you before you notice. If you know I'm gonna push you and you actively hold back, I can put the most force into you, given I got the strength.

 

[SIY]

Oh so it's just that it's not proportional, a.k.a. going from 300 Ohms to 16 Ohms will not multiply the current as much as going from 8 Ohms to 4 Ohms. Is that correct?

It is exactly proportional. 300 to 16 is a current increase of 300/16 = 18.75 times greater. 8 to 4 is 2 times greater.

Ohm's Law is Z (impedance) = V (voltage)/I (current). The math is pretty simple.

 

[JustAnAudioLover]

It is exactly proportional. 300 to 16 is a current increase of 300/16 = 18.75 times greater. 8 to 4 is 2 times greater.

Ohm's Law is Z (impedance) = V (voltage)/I (current). The math is pretty simple.

Ok so my first impression was right, but then does that mean most headphone amplifiers can just accommodate a 18x current increase going from 300 to 16 Ohms? And if so, why can't speaker amplifiers do the same?
Sorry if these seem like dumb questions but I have a hard time wrapping my head aroudn it...

 

[Lambda]

This seems pretty logical when you look at forums and reviews where people always tell that 300 Ohms headphones are "harder to drive" than, say, 16 Ohms headphones.

Well, people say this, but it's simply wrong.
The lower the impedance, the more current they need (for the same power), the harder they are to drive properly.

you can plug 16 Ohms IEMs on a tube amp designed for 300 Ohms headphones, which will have a high output impedance, and yes you'll hear some hiss (elevated noise floor) but no damage to the IEMs themselves.

You can’t say this with certainty. It depends—for example, on the listening level, amplifier, output impedance, and so on.


Everything being equal, a higher impedance headphone or speaker is easier to drive (puts less strain on the amplifier), and in general, better quality (lower THD+N).
But you might get lower max power (volume).


The other way around, you might compromise performance, and you might damage something. It depends. but you Maybe get more power

 

[SIY]

Ok so my first impression was right, but then does that mean most headphone amplifiers can just accommodate a 18x current increase going from 300 to 16 Ohms?

Note the difference in the size and current capability of speaker amplifiers versus headphone amps. Putting it in power terms (the product of voltage and current), it takes 100 times or more power to run a loudspeaker than a headphone. Speakers and headphones are VERY different, so it's not surprising that the electronics to drive them tend to be quite different.

 

[Scrivs]

Ok so my first impression was right, but then does that mean most headphone amplifiers can just accommodate a 18x current increase going from 300 to 16 Ohms? And if so, why can't speaker amplifiers do the same?
Sorry if these seem like dumb questions but I have a hard time wrapping my head aroudn it...

Legit question. Most folks wouldnt think twice (or even check the impedance spec) before plugging in almost any HP into an HPA.

Speaker amps, not so much.
I'm sure my Rumble 40 Bass amp wouldn't appreciate anothet set of drivers daisy chained to it.

 

[JustAnAudioLover]

Well, people say this, but it's simply wrong.
The lower the impedance, the more current they need (for the same power), the harder they are to drive properly.


You can’t say this with certainty. It depends—for example, on the listening level, amplifier, output impedance, and so on.


Everything being equal, a higher impedance headphone or speaker is easier to drive (puts less strain on the amplifier), and in general, better quality (lower THD+N).
But you might get lower max power (volume).


The other way around, you might compromise performance, and you might damage something. It depends. but you Maybe get more power

Makes sense that way, thanks!
So that means a "good" amplifier should be able to deliver twice as much power at 4 Ohms than it does at 8 Ohms right? In that case, why is Topping PA5 Plus (for instance) recommended when it seems to have roughly equivalent power levels at 4 vs 8 Ohms?

 

[NTK]

This picture from the video actually shows a bad analogy.

The electronic-hydraulic analogy equates voltage to pressure, flow resistance to electrical resistance, and volumetric flow rate to electrical current. However, an amplifier magnifies voltage according to its gain, which means output voltage = input voltage × gain. Therefore, it is the voltage that the amplifier works to maintain.

Using the hydraulic equivalent, the pump (amplifier) works to maintain the target pressure (voltage). If the flow resistance (electrical resistance) is low, the pump has to work very hard to maintain the target pressure (voltage) because that will require a high flow (current). That's why it is harder for a voltage amplifier to drive into a low impedance load, and is easier for it to drive into a high impedance load.

If the amplifier is a current amplifier (that tries to deliver a target current, which is NOT the case in standard audio implementations), the situation reverses.

 

[Sokel]

Since you are in the HP world, just think of the hard to drive low impedance headphones.
People get crazy enough to use speaker power amps to drive them.

 

[JustAnAudioLover]

Since you are in the HP world, just think of the hard to drive low impedance headphones.
People get crazy enough to use speaker power amps to drive them.

Well technically shouldn't speaker amplifiers be able to drive any headphone? Just put the amplifier's master volume at super low levels and it'll work fine! Right?

 

[Sokel]

Well technically shouldn't speaker amplifiers be able to drive any headphone? Just put the amplifier's master volume at super low levels and it'll work fine! Right?

Right. By why such a waste and more importantly risk?

 

[JustAnAudioLover]

Right. By why such a waste and more importantly risk?

Yeah I agree that's not a good idea, hence why I said "technically"

 

[Lambda]

So that means a "good" amplifier should be able to deliver twice as much power at 4 Ohms than it does at 8 Ohms right?

Well if there is no other botel neck... Yes but this obviously can't scale forever.

In that case, why is Topping PA5 Plus (for instance) recommended when it seems to have roughly equivalent power levels at 4 vs 8 Ohms?

Because it’s a good amp for 8ohm and AMPs are mostly Ranked by SINAD...
In my personal opinion an Speaker amp should heave like a ideal voltage source down to 4 ohme and for bursts down to 2 ohm... but thats just like my opinion.

Well technically shouldn't speaker amplifiers be able to drive any headphone? Just put the amplifier's master volume at super low levels and it'll work fine! Right?

You will get a lot of noise...