# What does putting low impedance headphone into a high gain amp do?



## clairyvic

Just wondering why it's bad and why you need to "match" low impedance to low gain? How does low impedance to high gain effect the sound?


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## Zenja

Damping factor is the ratio of load (headphone) impedance to source (amp output) impedance. A higher damping factor does a better job of controlling the speaker movement, especially around the resonance frequency. More importantly (IMO), if the speaker impedance varies along the frequency range, a lower damping factor impacts the frequency response. That is, if the damping factor is low and, for example, the speaker has a low impedance in the mid range but high in the treble, the amount of treble output will be different than the amount of midrange output. So this can easily make headphones sound very different with different amps if they have different output impedance.
   
  A damping factor of around 8-10 or more is usually considered sufficient. One nice thing about headphones is that many dynamic drivers have a very even impedance across the frequency range so the frequency response isn't affected much by low damping factor. Multi-driver IEMs with crossovers usually have a highly varying impedance so low damping factor is important there. Some headphones like the HD800 do too. Even worse, IEMs usually have low impedance so you need an amp with a good, low output impedance to make them sound proper. Many headphone amps (especially portable ones) (edit: ok, maybe not many) and the usual sources (such as phones, onboard computer outputs especially) have much too high output impedance for them.
   
  I'll give a specific example too. Plugging my JH13 into a receiver headphone out (they almost always have very high output impedance) makes them sound super bright.


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## clairyvic

Well what would happen from putting a low impedence headphone/iem into a high gain amp is what I meant. How would it effect the sound?


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## PurpleAngel

Quote: 





> Originally Posted by *Zenja* /img/forum/go_quote.gif
> Many headphone amps (especially portable ones) and the usual sources (such as phones, on-board computer outputs especially) have much too high output impedance for them.


 
  Portable amplifiers have too high an impedance? Which brands are you referring to?
  I also have a hard time with a blanket statement that (cell) phones have a high impedance, does not make sense.
  I agree that on-board audio at having high impedance.


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## Zenja

Quote: 





purpleangel said:


> Portable amplifiers have too high an impedance? Which brands are you referring to?
> I also have a hard time with a blanket statement that (cell) phones have a high impedance, does not make sense.
> I agree that on-board audio at having high impedance.


 
  I was doing research recently regarding output impedance of various phones. iPhones are one of the only ones I've encountered with very low numbers (like 2 or less). Many have around 10 ohms which is fine for many headphones but not for iEMs. Some popular ones (like Galaxy S2 and my Atrix) have around 40.
   
  As for portable amps, I looked at some before and encountered enough that had somewhat high output impedance. I've also heard others around here mention that many do. After looking up numbers for some of the more popular and well regarded ones, I take that claim back though.


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## PurpleAngel

Quote: 





zenja said:


> I was doing research recently regarding output impedance of various phones. iPhones are one of the only ones I've encountered with very low numbers (like 2 or less). Many have around 10 ohms which is fine for many headphones but not for IEMs. Some popular ones (like Galaxy S2 and my Atrix) have around 40.


 
  40-Ohms!, what cheap headphone outputs.
  Wonder what my Clip Zip and Sony E465 have for an output impedance?


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## proton007

Quote: 





clairyvic said:


> Well what would happen from putting a low impedence headphone/iem into a high gain amp is what I meant. How would it effect the sound?


 

 First of all, you risk damaging the headphone. There's a max power rating, beyond that you'll fry it.  For the same increase in voltage, a low impedance headphone will draw a lot more current, meaning more power transfer.
  Secondly, using higher gain sometimes has the effect of reducing the S/N ratio.


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## ExpatinJapan

Quote: 





purpleangel said:


> Portable amplifiers have too high an impedance? Which brands are you referring to?
> I also have a hard time with a blanket statement that (cell) phones have a high impedance, does not make sense.
> I agree that on-board audio at having high impedance.


 
   
  Quote: 





purpleangel said:


> 40-Ohms!, what cheap headphone outputs.
> Wonder what my Clip Zip and Sony E465 have for an output impedance?


 
  Here are some source and headphone amplifiers impedance charts
   
  http://monoadc.blog64.fc2.com/blog-entry-99.html


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## clairyvic

What does lowering the s/n ratio do, does that cause that strange buzzing noise ?


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## proton007

Quote: 





clairyvic said:


> What does lowering the s/n ratio do, does that cause that strange buzzing noise ?


 

 More like a hiss. For example the 'snow' in tv signals.
  The buzzing noise is a 'hum', probably made by grounding issues.


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## thekenner33

Quote: 





zenja said:


> Damping factor is the ratio of load (headphone) impedance to source (amp output) impedance. A higher damping factor does a better job of controlling the speaker movement, especially around the resonance frequency. More importantly (IMO), if the speaker impedance varies along the frequency range, a lower damping factor impacts the frequency response. That is, if the damping factor is low and, for example, the speaker has a low impedance in the mid range but high in the treble, the amount of treble output will be different than the amount of midrange output. So this can easily make headphones sound very different with different amps if they have different output impedance.
> 
> A damping factor of around 8-10 or more is usually considered sufficient. One nice thing about headphones is that many dynamic drivers have a very even impedance across the frequency range so the frequency response isn't affected much by low damping factor. Multi-driver IEMs with crossovers usually have a highly varying impedance so low damping factor is important there. Some headphones like the HD800 do too. Even worse, IEMs usually have low impedance so you need an amp with a good, low output impedance to make them sound proper. Many headphone amps (especially portable ones) (edit: ok, maybe not many) and the usual sources (such as phones, onboard computer outputs especially) have much too high output impedance for them.
> 
> I'll give a specific example too. Plugging my JH13 into a receiver headphone out (they almost always have very high output impedance) makes them sound super bright.


 
  This post was very helpful to me thank you.  I have another question though, what is the difference between headphone impedance and sensitivity?  I know they are completely different units, Ohms and Db, but don't they give you similar information?  Thanks for the help.


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## Zenja

Quote: 





thekenner33 said:


> This post was very helpful to me thank you.  I have another question though, what is the difference between headphone impedance and sensitivity?  I know they are completely different units, Ohms and Db, but don't they give you similar information?  Thanks for the help.


 
  I'd say they don't really give similar information, though headphones with lower impedance often have higher sensitivity. It's best to look at them separately though.
   
  Higher impedance headphones can be good because they're not as sensitive to the output impedance of the amp, and also because they usually don't hiss as much when the amp is nosiy. This is because noise usually has a certain voltage level for a given amp (and doesn't change much with volume) and higher impedance headphones require more voltage for the music to be the same loudness, so the noise is relatively smaller signal. Don't confuse this as meaning the amp needs to have more power though - the voltage is higher (so yes, it needs more gain, which describes how much the amp multiplies the voltage coming into it), but the current is lower because of the higher impedance, so the power (which is voltage * current) can be about the same.
   
  Sensitivity on the other hand determines how loud the headphones will be for a given amount of power, so it's possible for low sensitivity headphones to need a more powerful amp. For example, JH16 IEMs have 116dB at 1mW power. That's a really loud volume for a very small amount of power (most things can provide that). HE-6 have I think 84 dB output at 1mW. That's a huge difference. For the HE-6 to be as loud as the JH16, it needs more than 1000 times as much power.


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## thekenner33

Quote: 





zenja said:


> I'd say they don't really give similar information, though headphones with lower impedance often have higher sensitivity. It's best to look at them separately though.
> 
> Higher impedance headphones can be good because they're not as sensitive to the output impedance of the amp, and also because they usually don't hiss as much when the amp is nosiy. This is because noise usually has a certain voltage level for a given amp (and doesn't change much with volume) and higher impedance headphones require more voltage for the music to be the same loudness, so the noise is relatively smaller signal. Don't confuse this as meaning the amp needs to have more power though - the voltage is higher (so yes, it needs more gain, which describes how much the amp multiplies the voltage coming into it), but the current is lower because of the higher impedance, so the power (which is voltage * current) can be about the same.
> 
> Sensitivity on the other hand determines how loud the headphones will be for a given amount of power, so it's possible for low sensitivity headphones to need a more powerful amp. For example, JH16 IEMs have 116dB at 1mW power. That's a really loud volume for a very small amount of power (most things can provide that). HE-6 have I think 84 dB output at 1mW. That's a huge difference. For the HE-6 to be as loud as the JH16, it needs more than 1000 times as much power.


 
  Okay i think i see, so the JH16 IEMs require less power to achieve the same volume than the HE-6, _and_ to achieve that power requires less output voltage from an amp because the impedance is less than the HE-6.  So its a much more efficient headphone, although maybe not as controlled as the JH16.


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