Headphone impedance and sensitivity

[rooster81]

Hi everyone! I'm trying to learn about impedance and sensitivity for headphones. One of my main questions is this; if my headphones are loud enough does that mean they are being properly driven? Or is it possible that headphones need more power to drive them "properly" even though they are loud?

I have a pair of DT 770s that are 250 OHM. They sound great to me plugged straight into my phone or fiio BTR3K. But from some things I'm reading it sounds like at 250 OHMs they should need more power. Is that where sensitivity comes in?

Thanks in advance for any replies!

 

[DVDdoug]

One of my main questions is this; if my headphones are loud enough does that mean they are being properly driven? Or is it possible that headphones need more power to drive them "properly" even though they are loud?

If they go loud enough without hearing URL='https://en.wikipedia.org/wiki/Clipping_(audio)']clipping[/URL] (distortion) from your amplifier, everything is cool! Clipping is the most common kind of distortion and you can get it by turning-up the volume too loud... like trying to get 15 Watts out of a 10W amplifier.

If you have something with a built-in DAC like a phone or computer, they are usually designed so even at maximum digital volume the analog amplifier isn't maxed-out and it won't clip. (The digital data can be clipped if you boost the bass digitally, or something like that.)


P.S.
Getting at your "impedance" question, I'm going to throw a little electronics & math at you...

Amplifiers are "constant voltage" devices. The voltage isn't really constant because it varies with loudness moment-to-moment. But, the voltage is mostly independent of the load impedance up to the point where it can't supply the current.

Current flows through wires & resistance and resistance (or impedance) is "the resistance to current flow". Higher resistance or impedance means less current with the same voltage. Lower impedance means more current.

Ohm's Law defines the relationship between Voltage, Resistance (or impedance), and Current as Current = Voltage / Resistance.
Power (Wattage) is calculated as Power = Voltage x Current.
From those two formulas you can derive Power = Voltage squared / Impedance.

So, if you cut the impedance in half and maintain the voltage you get double the wattage. If two headphones have the same efficiency (converting electrical power into sound power), but one has half the impedance, the one with lower impedance will be dissipating twice the power and it will be louder!

So as a generalization, lower impedance headphones tend to be louder.

But of course headphones have different efficiency (usually specified as "sensitivity" with a voltage reference). Planar headphones tend to be low impedance and low sensitivity, but dynamic headphones vary too.

 

[rooster81]

If they go loud enough without hearing URL='https://en.wikipedia.org/wiki/Clipping_(audio)']clipping[/URL] (distortion) from your amplifier, everything is cool! Clipping is the most common kind of distortion and you can get it by turning-up the volume too loud... like trying to get 15 Watts out of a 10W amplifier.

If you have something with a built-in DAC like a phone or computer, they are usually designed so even at maximum digital volume the analog amplifier isn't maxed-out and it won't clip. (The digital data can be clipped if you boost the bass digitally, or something like that.)


P.S.
Getting at your "impedance" question, I'm going to throw a little electronics & math at you...

Amplifiers are "constant voltage" devices. The voltage isn't really constant because it varies with loudness moment-to-moment. But, the voltage is mostly independent of the load impedance up to the point where it can't supply the current.

Current flows through wires & resistance and resistance (or impedance) is "the resistance to current flow". Higher resistance or impedance means less current with the same voltage. Lower impedance means more current.

Ohm's Law defines the relationship between Voltage, Resistance (or impedance), and Current as Current = Voltage / Resistance.
Power (Wattage) is calculated as Power = Voltage x Current.
From those two formulas you can derive Power = Voltage squared / Impedance.

So, if you cut the impedance in half and maintain the voltage you get double the wattage. If two headphones have the same efficiency (converting electrical power into sound power), but one has half the impedance, the one with lower impedance will be dissipating twice the power and it will be louder!

So as a generalization, lower impedance headphones tend to be louder.

But of course headphones have different efficiency (usually specified as "sensitivity" with a voltage reference). Planar headphones tend to be low impedance and low sensitivity, but dynamic headphones vary too.

So if I were to try an analogy, if electricity were water then impedance is like the size of the hose?

If that's correct, what would sensitivity be?

Thanks!

 

[unpluggged]

If that's correct, what would sensitivity be?

Probably the weight of an obstacle (a leaf) the water hits on its way, that determines how far it would be pushed away But why do you need such a forced and artificial analogy?

 

[NTK]

So if I were to try an analogy, if electricity were water then impedance is like the size of the hose?

If that's correct, what would sensitivity be?

Thanks!

The electricity / water flow analogy equates water pressure to voltage, flow restriction to resistance, and flow rate to current.

However, for headphone drivers, the sound pressure output depends on more than just the amount of current. It also depends on the moving mass, magnetic field strength, mechanical compliance, and the "effective length" of the voicecoil (for dynamic drivers; balanced armature drivers/planar magnetic/e-stats have very different characteristics). The voicecoil length and cross-sectional area in turn affect the impedance (and therefore current) and mass. So, the relationship of voltage to SPL (and electrical power to SPL) is much more complicated than the simple water flow analogy.

 

[rooster81]

Probably the weight of an obstacle (a leaf) the water hits on its way, that determines how far it would be pushed away But why do you need such a forced and artificial analogy?

Because I'm daft.

 

[rooster81]

Came across this article that states "Higher-impedance headphones require more voltage to work properly, so portable, energy-efficient devices can’t run them correctly" and "Driving headphones loudly doesn’t mean efficiently".

What is Headphone Impedance? High vs. Low, Sensitivity, and More

Impedance can affect the sound quality of your headphones, but not in terms of loudness. Learn everything you need to know before buying an amp.

headphonesaddict.com

However later in the article he also notes there are only minor improvements with an amp and in a separate article states that the HD650s can be easily driven by a smart phone.

So these are a few examples of things that are confusing me, because I've always read that headphones like the HD650s are hard to drive because of their high IMPEDANCE but some sources say a phone is fine to drive them because they have low SENSITIVITY.

Thanks again!

 

[Soandso]

… "Driving headphones loudly doesn’t mean efficiently".…

Before mobile audio devices stationary amplifiers would supply adequate voltage to headphone voice coils having many turns of relatively fine wire (creating high impedance) which allowed operational heat dissipation that limited the incidence(s) of distortion. With portable audio amplification there were limits to voltage supply and headphones having relatively less wire coils (low impedance) became practical with a trade off getting relatively louder with less voltage. But the low impedance headphones gets by with less wiring which make heat dissipation a more complex factor leading to potential incidences of distortion.

Device impedance changes with sound frequency (except for planar magnetic headphone designs) so as turn up the music through modern small amplifiers then potentially this induces distortion of some frequencies. Thus cell phones may sound better with an added on portable amplifier to give low impedance headphones more ability to swing voltage and allay distortion.

Design factors among headphones' internals account for different sensitivity. In the above context better sensitivity headphones have better response to any supplied amplification voltage with regards to transitory changes of frequency impedance. Put simply: for getting your preferred listening volume (SPL, sound pressure level) better sensitivity means less voltage is required leading to minimal voice coil heat and less potential distortion.

 

[rooster81]

Before mobile audio devices stationary amplifiers would supply adequate voltage to headphone voice coils having many turns of relatively fine wire (creating high impedance) which allowed operational heat dissipation that limited the incidence(s) of distortion. With portable audio amplification there were limits to voltage supply and headphones having relatively less wire coils (low impedance) became practical with a trade off getting relatively louder with less voltage. But the low impedance headphones gets by with less wiring which make heat dissipation a more complex factor leading to potential incidences of distortion.

Device impedance changes with sound frequency (except for planar magnetic headphone designs) so as turn up the music through modern small amplifiers then potentially this induces distortion of some frequencies. Thus cell phones may sound better with an added on portable amplifier to give low impedance headphones more ability to swing voltage and allay distortion.

Design factors among headphones' internals account for different sensitivity. In the above context better sensitivity headphones have better response to any supplied amplification voltage with regards to transitory changes of frequency impedance. Put simply: for getting your preferred listening volume (SPL, sound pressure level) better sensitivity means less voltage is required leading to minimal voice coil heat and less potential distortion.

Thanks for the response!