Amp Output Impedance Headphone Matching?

[Kitmellow]

Forgive me if this is in the wrong place, but I've looked around and still don't understand this concept and what it means. derp. 

 
I am new to amps and I understand that some drivers especially ones with higher resistance (ohms) require amps to function their best. But I did not anticipate that there was another factor about amp output impedance and what it means to have to match the drivers to be with the most compatible amp, or else they might "sound improper while driven though the amp" such as sounding too sibilant or bassy.
 
End are the times where I thought "Headphones too quiet and/or too compressed-sounding? Just get an amp, any ol' amp will be fine." 

 
I know that certain amps have a reputation of sound warmer or cooler than others too. Perhaps there's a relationship there between amp output impedance and sound signature tilting of a given headphone/earphone being driven through them? 
 
I also read that balanced armature designs can have drastic changes in electrical impedance across the frequency ranges versus dynamic drivers which are mostly linear, which is even more confusing because that suggests a dynamic impedance ohms value compared to the static ohms value that is given in the specs of any headphones/earphones?
 
I'm clearly missing the big picture. How is this all related in non-super technical terms?

 

[ProtegeManiac]

Quote:

Originally Posted by Kitmellow /img/forum/go_quote.gif

 

I am new to amps and I understand that some drivers especially ones with higher resistance (ohms) require amps to function their best. But I did not anticipate that there was another factor about amp output impedance and what it means to have to match the drivers to be with the most compatible amp, or else they might "sound improper while driven though the amp" such as sounding too sibilant or bassy.

 

When your amp's output impedance is higher than the nominal load (ie in some cases the impedance changes depending on what frequency is playing) it causes the amp to get a lower damping factor, ie, how well it can control the movement of the transducers it is sending the amplified signal to.

 

Safe ratio that's being touted around is that your nominal impedance rating should be eight times that of the output impedance, but you don't really need to absolutely stick to that ratio. If you're close enough then likely there won't be any problems. Also, if you're starting out with a high impedance to begin with, you won't even need to follow that ratio - for example a 300ohm headphone won't be as affected by 120ohm output impedance as a 32ohm headphone, but of course there are other factors at play, like power delivery (some amps will deliver more power at 300ohms than at 32ohms, and vice versa).

 

 

Quote:

Originally Posted by Kitmellow /img/forum/go_quote.gif

 

I know that certain amps have a reputation of sound warmer or cooler than others too. Perhaps there's a relationship there between amp output impedance and sound signature tilting of a given headphone/earphone being driven through them? 

 

It depends on a lot of other factors that are harder to predict - how the amp behaves given that nominal load, how dynamic (erratic) that load is, what the nominal load is to begin with, etc. For the latter, in most cases 

 

 

 

Quote:

Originally Posted by Kitmellow /img/forum/go_quote.gif

 

I also read that balanced armature designs can have drastic changes in electrical impedance across the frequency ranges versus dynamic drivers which are mostly linear, which is even more confusing because that suggests a dynamic impedance ohms value compared to the static ohms value that is given in the specs of any headphones/earphones?

 

Not sure where you got that info, but if anything it potentially can be due to highly complex crossover designs, something that single fullrange driver designs like a typical headphone won't need to deal with. That said, this is more along the lines of having a complex load due to dynamic drivers that have a very dynamic (erratic) impedance. Balanced armatures do not behave in the same manner and thus aren't as prone to having a badly designed crossover make their impedance swings worse.

 

 

 

Quote:

Originally Posted by Kitmellow /img/forum/go_quote.gif

 

I'm clearly missing the big picture. How is this all related in non-super technical terms?

 

It will be like a certain girl of low load impedance only pretending to be low maintenance so she can cut high output impedance guy's hair, at which point his legs kinda turn to jelly and he can't punch anymore (can't mention names because as long as it's from that part of the world it's forbidden, but apparently Schiit can do the same with Norse myths; in any case if you pay attention on Sundays then you'd know what I'm referring to).

 

[Me x3]

  Forgive me if this is in the wrong place, but I've looked around and still don't understand this concept and what it means. derp. 

 
I am new to amps and I understand that some drivers especially ones with higher resistance (ohms) require amps to function their best. But I did not anticipate that there was another factor about amp output impedance and what it means to have to match the drivers to be with the most compatible amp, or else they might "sound improper while driven though the amp" such as sounding too sibilant or bassy.
 
End are the times where I thought "Headphones too quiet and/or too compressed-sounding? Just get an amp, any ol' amp will be fine." 

 
I know that certain amps have a reputation of sound warmer or cooler than others too. Perhaps there's a relationship there between amp output impedance and sound signature tilting of a given headphone/earphone being driven through them? 
 
I also read that balanced armature designs can have drastic changes in electrical impedance across the frequency ranges versus dynamic drivers which are mostly linear, which is even more confusing because that suggests a dynamic impedance ohms value compared to the static ohms value that is given in the specs of any headphones/earphones?
 
I'm clearly missing the big picture. How is this all related in non-super technical terms?

 
Impedance vs Frequency graph is not perfectly flat in the vast majority of cases (headphones)
If the Damping Factor (Headphone Impedance (you can use its minimum) divided by Amplifier Output Impedance) is not over 8 there's a chance you'll hear the effects of the interaction between the headphone and the amplifier.
 
The main effect caused by low Damping Factor is Equalization in the shape of the Headphone's impedance.
 
Most quality dynamic headphones (HD598/HD600/HD650/DT880/DT990/T1/HD700/HD800...) have a bump in the impedance plot at mid-bass frequencies. Then if you pair them with a high output impedance amplifier (like some tube amplifiers or the headphone jack on many receivers) you'll get a poor damping factor and a boosted mid-bass/warmer tone/not as precise overall but some would say "more musical"
 
The shape of the impedance curve is very important. For instance, DT880 has a slight bump in the mid-bass and thus the effect is subtle, even when plugged into amplifiers with really high output impedance (say 200 Ohm). On the other hand the HD600 has a bigger bump in the impedance plot (mid-bass region) and thus this effect is not as subtle.
 
That's why you don't want a poor damping factor when using BA IEMs, their impedance varies quite a lot across the spectrum and can have several spikes here and there, and you really don't want that kind of equalization applied to their smooth frequency response.

 

[tomb]

These conversations about amplifier output impedance and damping factor always seem to miss half of the subject: what happens when the headphone driver is over-damped?  There are indications that this could be a loss of bass and perhaps strident, harsh mids/highs, which seem to be a trait of many simpler solid-state amplifiers.
 
Nelson Pass had this very interesting article about current-drive and single, full-frequency drivers (very similar to the conditions of headphone drivers) years ago:
http://audioxpress.com/article/Current-Source-Amps-and-Sensitive-Full-Range-Drivers.html

 

[Me x3]

  These conversations about amplifier output impedance and damping factor always seem to miss half of the subject: what happens when the headphone driver is over-damped?  There are indications that this could be a loss of bass and perhaps strident, harsh mids/highs, which seem to be a trait of many simpler solid-state amplifiers.
 
Nelson Pass had this very interesting article about current-drive and single, full-frequency drivers (very similar to the conditions of headphone drivers) years ago:
http://audioxpress.com/article/Current-Source-Amps-and-Sensitive-Full-Range-Drivers.html

For most dynamic headphones, low damping factor means the amplifier won't provide a flat frequency response to the headphone. 
You might like the result or not depending on the headphone and your preferences.
 
I can't see a good point to tweak this topic towards an objective territory where we all agree on how much bass headphones should have, because there's no such territory (given the vast number of very different recordings and the key role of personal preferences)
 
I'm not against low damping factor pairings, if you like the results and enjoy your music, that's great.
I used to enjoy my DT880s plugged into a Yamaha integrated amplifier with 470 Ohm output impedance at the headphone jack (warmer and not as clear in the bass)
 
I'm against the "you should use the headphone X with an output impedance over Y, because if you don't you'll lose bass and so on..."
 
I think flat amplifier should be the reference, then a coloured/not flat amplifier (aka high output impedance amplifier) might add or subtract bass/mids/treble, but not the other way around. A flat amplifier won't make you lose bass quantity, a flat amplifier will provide the exact level of bass. Then if you don't like the frequency response of your headphone driven by a flat amplifier, you are free to pick a coloured/not flat amplifier that you like better.
 
For most dynamic headphones:
High Damping Factor = The amplifier provides a flat response
Low Damping Factor = The amplifier provides a coloured frequency response depending the headphone's impedance (vs frequency) plot.
 
I don't see how half of the explanation might be missing.

 

[Kitmellow]

 

 

It will be like a certain girl of low load impedance only pretending to be low maintenance so she can cut high output impedance guy's hair, at which point his legs kinda turn to jelly and he can't punch anymore (can't mention names because as long as it's from that part of the world it's forbidden, but apparently Schiit can do the same with Norse myths; in any case if you pay attention on Sundays then you'd know what I'm referring to).

 
Wow, I think I'm going to take everything I know about life and throw it out the window. If I knew what you were referring to, then I think I would be Jesus. 

 
 
 
Thanks for all the great replies. I've gathered some more info and everything I've been wondering about is pretty much solved. The 1/8th rule of minimum headphone impedance to amp output impedance seems to be popping up everywhere and apparently some people even recommend 1/10 for overhead.
 
If anybody else happens to find this thread with a similar question, I recommend these 2 excellent sources: http://nwavguy.blogspot.ca/2011/02/headphone-amp-impedance.html and lachlanlikesathing's post at https://www.reddit.com/r/headphones/comments/27mowj/output_impedance_is_it_really_that_important/
 
 
I guess my only questions that remain are: Does output impedance apply in the same way to unamped sources like standalone DACs? They have the same phenomenon just with lesser output/current right?
 
Does using an amp through a DAC & AMP combo make any sense? If the goal is to change the high output impedance of the DAC & AMP combo through a low output impedance amp? Or will there be incompatibilities like being too loud through the double amp?

 

[ProtegeManiac]

 
I guess my only questions that remain are: Does output impedance apply in the same way to unamped sources like standalone DACs? They have the same phenomenon just with lesser output/current right?

 
What do you mean, the output impedance of a DAC/CDP and the input impedance of an amplifier? That matters also, except that in practice you will not encounter any DAC/CDP/TTphonopreamp nor amplifier with a problem on their output or input impedance (respectively), unlike how older speaker amps have a headphone driver with a high output impedance and then later on you start seeing headphones with impedance loads a lot lower than that.
 
 

 
Does using an amp through a DAC & AMP combo make any sense? If the goal is to change the high output impedance of the DAC & AMP combo through a low output impedance amp? Or will there be incompatibilities like being too loud through the double amp?

 
Well if you already had the DAC-HPamp unit, but realized now that there's a problem with its output impedance for some headphones, then if it has a line out then you might as well hook up an amp to that than buy a new DAC and amp or DAC-HPamp.

 

[tomb]

 

  These conversations about amplifier output impedance and damping factor always seem to miss half of the subject: what happens when the headphone driver is over-damped?  There are indications that this could be a loss of bass and perhaps strident, harsh mids/highs, which seem to be a trait of many simpler solid-state amplifiers.
 
Nelson Pass had this very interesting article about current-drive and single, full-frequency drivers (very similar to the conditions of headphone drivers) years ago:
http://audioxpress.com/article/Current-Source-Amps-and-Sensitive-Full-Range-Drivers.html

For most dynamic headphones, low damping factor means the amplifier won't provide a flat frequency response to the headphone. 
You might like the result or not depending on the headphone and your preferences.
 
I can't see a good point to tweak this topic towards an objective territory where we all agree on how much bass headphones should have, because there's no such territory (given the vast number of very different recordings and the key role of personal preferences)
 
I'm not against low damping factor pairings, if you like the results and enjoy your music, that's great.
I used to enjoy my DT880s plugged into a Yamaha integrated amplifier with 470 Ohm output impedance at the headphone jack (warmer and not as clear in the bass)
 
I'm against the "you should use the headphone X with an output impedance over Y, because if you don't you'll lose bass and so on..."
 
I think flat amplifier should be the reference, then a coloured/not flat amplifier (aka high output impedance amplifier) might add or subtract bass/mids/treble, but not the other way around. A flat amplifier won't make you lose bass quantity, a flat amplifier will provide the exact level of bass. Then if you don't like the frequency response of your headphone driven by a flat amplifier, you are free to pick a coloured/not flat amplifier that you like better.
 
For most dynamic headphones:
High Damping Factor = The amplifier provides a flat response
Low Damping Factor = The amplifier provides a coloured frequency response depending the headphone's impedance (vs frequency) plot.
 
I don't see how half of the explanation might be missing.

Then you need to re-read what I posted and also Nelson Pass's comments.
 
For every driver, there exists an optimum damping solution.  By perfect corollary, that means there is an under-damped condition and an over-damped condition.
 
In the race toward super-low output impedance for amplifiers, one half of the system description is almost never discussed - the over-damped condition.  It has consequences that affect frequency response, too.
 
My point (besides no one ever talks about one-half of the system description), is that the below is a huge assumption, nothing more:

For most dynamic headphones:
High Damping Factor = The amplifier provides a flat response
Low Damping Factor = The amplifier provides a coloured frequency response depending the headphone's impedance (vs frequency) plot

 
You state that "flat amplifier should be the reference," but that's exactly the point: you go on to describe that damping factor affects whether that amplifier is flat with a given headphone driver.  That's the real issue regarding amplifiers in the analog business of reproducing sound: whether the combination of source, amplifier, and driver all combine to produce the best frequency response.  There would be no discussion at all around here and elsewhere if that were not the case.
 
Anyway, I'm just attempting to put up a marker that the race toward super-low output impedance with amplifiers is not necessarily the best goal in all cases.

 

[Me x3]

  Then you need to re-read what I posted and also Nelson Pass's comments.
 
1) For every driver, there exists an optimum damping solution.  By perfect corollary, that means there is an under-damped condition and an over-damped condition.
 
In the race toward super-low output impedance for amplifiers, one half of the system description is almost never discussed - the over-damped condition.  It has consequences that affect frequency response, too.
 
My point (besides no one ever talks about one-half of the system description), is that the below is a huge assumption, nothing more:
 
2) You state that "flat amplifier should be the reference," but that's exactly the point: you go on to describe that damping factor affects whether that amplifier is flat with a given headphone driver.  That's the real issue regarding amplifiers in the analog business of reproducing sound: whether the combination of source, amplifier, and driver all combine to produce the best frequency response.  There would be no discussion at all around here and elsewhere if that were not the case.
 
3) Anyway, I'm just attempting to put up a marker that the race toward super-low output impedance with amplifiers is not necessarily the best goal in all cases.

 
1) 
What I say is that the "optimum damping solution" determines a frequency response that you may like better or not depending on the headphone + your personal preferences + your recordings. Then we can not say that's the optimum.
 
(It could be the optimum for the sake of an experiment/measurement but not optimum when it comes to practical purposes since there are other important variables involved)
 
Pick a bassy recording and a K702 driven with high damping factor and it would suit it very well, pick a really bass light recording and the HD650 driven with a 100 Ohm (output impedance) amplifier might be more realistic. 
 
2)
Damping factor affects whether the amplifier is flat or not because of the interaction between the amplifier's output impedance and the (variable across the spectrum) headphone's impedance.
That's fact, 100% measurable.
 
I think flat amplifier should be the reference because there's no good reason to pick a different reference.
Flat is flat, for you, for me, for everyone since it's something easily measurable and easily applicable to each and every headphone.
 
Reference doesn't mean optimum for everyone's preferences/headphones/recordings, that's for sure.
 
You can go ahead and make a Table of the  "optimum" damping for each and every headphone.
Then use those parameters (combination between amplifiers' output impedance and headphones) as a new reference.
 
After a lot of work, the new (damping optimized) reference still won't be the optimum for everyone's preferences/headphones/recordings, and now it's more tricky to apply.
 
a- Pick a headphone
b- Go to the Optimum damping solution table
c- Find an amplifier with the exact output impedance 'needed' for your headphone
d- If you are lucky enough to find one, then listen and decide whether you like it or not.
 
I'm not saying this would be useless, I think it might be interesting indeed. Just not that practical for the sake of reference.
 
3)
We agree. 
Different headphones, personal preferences and recordings play key roles when it comes to perceived sound quality.
There's no such a thing as the Perfect output impedance number applicable to every headphone and every person and thus the " lower means better " can't remain true for all cases.
 
People normally tend to oversimplify these kind of phenomena to create an ilusion of understanding.
 
I've spent several minutes the other day writing to someone who claimed the m9XX was significantly better than the Magni 2 Uber due to the much higher damping factor
(0.08 Ohm vs 0.2 Ohm) !!
 
Regards.