[SanjiWatsuki]

Hello, Head-Fi Sound Science forum. I've been doing a lot of research on amplifiers and damping factor and this question has very much bugged me. I'm wondering if you guys think my logic is solid. 
 
Allow me to say first off that there is no room to doubt that low impedance headphones/earphones, such as balanced IEMs or highly efficient portable headphones, will be greatly affected by high source impedance. Their frequency response will be all messed up, their sound decay time might double in length making their bass muddy and "loose", their crossovers will fail, etc. What I'm concerned with, however, is the effect of a high impedance headphone out (~50 ohms, a number found often in low cost headphone amps and the headphone out of professional audio equipment) on the sound of higher impedance headphones, anything from 50 to 600.
 
To start, let's focus on the frequency response aspect. This part is relatively easy if there is a published impedance chart for the headphones. We can take the maximum impedance, add in the source impedance, and calculate the change in dB and do the sound for the lowest impedance. Using a combination of these two values we can determine a range that the sound changed based upon the source impedance mathematically. Here's an example:
 
Using Tyll's chart for the Grado SR60i, we'll measure the dB differences in this low 32ohm impedance headphone when fed a 50ohm source impedance amplifier. The lowest impedance appears to be 32 and the highest appears to be 42. We will assume a 1 volt source.
Voltage at 32 ohm: 32 / (32 + 50) = .39
Voltage at 42 ohm: 42 / (42 + 50) = .457
Frequency response deviation: 20 * log (.457/.39) = 1.38dB
 
So, at one volt, we experience only a 1.38dB variation in sound -- basically, barely audible for this highly efficient headphone that doesn't require an amp. Results will, of course, differ headphone to headphone. Furthermore, there can be some massive loss in voltage if the headphone is of a lower impedance than the amp, but that's very difficult to predict how much will be lost. The gist of what I'm saying is that, if you can calculate a small difference in the frequency response, this aspect of headphone impedance can be ignored.
 
--
 
The next important aspect of output impedance is the electrical damping factor. Think of it as the amount of control the amplifier has on the driver. The lower the damping factor, the more the driver will vibrate after it isn't supposed to vibrate. The question is how much damping factor is needed and how much does it affect the sound quality?
 
I found this study on the effect of damping factor on speakers for this aspect. Granted, these are speakers and not headphones but the general principles apply. The main thing in my mind when I was reading this was that, because of the lower mass of headphone drivers, the less of an effect electrical damping will have on it. The driver has less mass moving and, therefore, will be less affected by damping factor. I feel Tyll's graphs for him testing the DT 48e at his normal testing impedance and then again with a 120 ohm source impedance (damping factor of .208) backs me up with this idea. The differences between the impulse decay time and the difference in time for it to make the sine waves changed in what appears to be an insignificant time. Furthermore, just the overall impulse response time for headphones just seems much lower than the decay time for speakers. Granted, these are different testing mechanisms and the numbers are not completely compatible, but I think it conveys the gist of the idea. Therefore, we can assume the differences in decay time for speakers is of some level of magnitude greater than it would be for headphones.
 
The study I linked came to the conclusion that any damping factor over 10 could safely be said to have no audible differences. Given that the decay differences is some degree of magnitude greater than it would be for speakers, it seems logical that a damping factor closer to the range of 1 to 3 would safely result in non-audible differences due to the amplifier's control over the driver. If we take the extreme and divide the decay time of the speaker by a Tyll impulse response time and multiply it by the damping factor of 10, the number would be significantly under 1, but that doesn't seem to be a logical step to take.
 
--
 
Heading onto the further implications of these conclusions, let's observe if the HD 650 could be capably powered by a $19 Behringer Micromon MA400 headphone amp. We will try to power it to 110 peak SPL ( Antilog ( ( 110 – 103) / 20 )  = 2.2 Vrms ). The Behringer spec sheet says it has . We calculate Vrms from dBu by antilog (dBu / 20) * .775 = V. Given that the dBu is +10, we can find the rated output to be 2.45Vrms -- more than enough to power the HD 650 to 110 peak SPL! Next, we'll calculate the frequency response changes.
 
From Tyll's charts for the HD 650, we know the lowest impedance to be around 300ohm and the highest to be around 520ohm.
Voltage at 300 ohm: 300 / (300 + 30) = .91
Voltage at 520 ohm: 520 / (520 + 30) = .945
Frequency response deviation: 20 * log (.945/.91) = 0.27dB
 
There is an inaudible frequency response change at 0.27dB.
 
Finally, the damping factor of the headphone is 10 -- effectively inaudible. Assuming the Behringer Micromon MA400 amp has distortion below audible levels, it is a  $20 desktop amp which should be able to power the Sennheiser HD650.
 
Is this a logical conclusion? Just wanted to make sure I wasn't going crazy.
 

 

[fubar3]

You have a thoughtful post but it hints that there is a problem which I think has already been solved. Why not just buy or build a low-Z headphone amp which removes the worry of impedance matching. The DIYs available these days are high quality.

 

[SanjiWatsuki]

I agree, the DIY kits are great and outperform a lot of the commercial amps. Part of the issue is that not everyone has the access or knowledge to pull off the soldering required for some of the DIY project and, if you got a pre-built DIY headphone amp, they are still relatively pricey -- JDSLabs Cmoy runs $60, O2 will run $150, and the Mini-3 (which has a 10 ohm impedance anyway) will run $180.
 
As for buying a low impedance headphone amp with high output, they exist but they are even more expensive than buying a pre-built DIY option. Virtually every single under $100 commercial headphone amp with more than 2V output an output impedance of 50 to 100. Beyond the Fiio E10 (which really does appear to be a good deal with its Wolfson DAC), which likely has the same 0.5 ohm impedance of its E11 brother and probably caps out under 3V, I don't think any budget high-power low-impedance amps out of DIY really exist. 
 
I mostly went through this to try and figure out just how acceptable the output of the cheap sub-$60 headphone amps on the market truly were by the numbers and if they looked like they were sufficient to power high impedance somewhat-difficult-to-drive cans.

 

[RexAeterna]

i wouldn't worry about ti too much when dealing with dynamic drivers. dynamics impedance vary all the time with frequency. speakers never have any issues cause speaker output impedances are always close to 0ohms(for well built solid state of course) and dynamic driver vary with frequency. i usually just go by the 1/8 rule most of the time. like 1/8 of 600ohms is 75 and so forth. i heard of over dampening as well which most people don't mention.

i have used headphones before with very high output impedances of 680ohms but never ran issues with low impedance headphones due to the ability of the power transformer matching the impedance of the headphone. tubes and op-amps are different. while tubes highly rely on output power transformers to give their given output impedance, and while op-amps has a fix output impedance as well. a discrete solid state amp with a large(or some cases dual) transformer(s) not only acts by blocking EMI and giving the amp it's maximum voltage output but matches impedances as well,since the transformer can increase and decrease it given power with certain loads to try to match it.


i would only be concern with electrical dampening with tubes and op-amps. with discrete solid state builds not much of an issue really. you should be more concern on it's maximum output voltage at it's given output impedance.

 

[SanjiWatsuki]

I was mostly thinking about eschewing the 1/8 rule due to the results from the study. It was speakers, and speakers are standardized, but in this case the speakers were given poor dampening ratios to measure the differences between high and low dampening. Given the greater mass of the speaker driver, I would assume that the effects would be even less evident in the tiny headphone drivers. I'm just questioning whether or not even a dampening ratio of 8 is necessary if there are no significant frequency response changes in op-amp based amplifiers -- it's difficult to impossible to find solid-state on a really low budget. I'm trying to question whether or not electrical dampening on op-amp based amplifiers is a significant factor for dampening ratios in the range of 1 to 5, basically.
 
As for overdampening, it is more of a thing that occurs from a mechanical perspective, commonly in the modding community, I don't believe you can overdampen electrically. 
 
Quote:

i wouldn't worry about ti too much when dealing with dynamic drivers. dynamics impedance vary all the time with frequency. speakers never have any issues cause speaker output impedances are always close to 0ohms(for well built solid state of course) and dynamic driver vary with frequency. i usually just go by the 1/8 rule most of the time. like 1/8 of 600ohms is 75 and so forth. i heard of over dampening as well which most people don't mention.
i have used headphones before with very high output impedances of 680ohms but never ran issues with low impedance headphones due to the ability of the power transformer matching the impedance of the headphone. tubes and op-amps are different. while tubes highly rely on output power transformers to give their given output impedance, and while op-amps has a fix output impedance as well. a discrete solid state amp with a large(or some cases dual) transformer(s) not only acts by blocking EMI and giving the amp it's maximum voltage output but matches impedances as well,since the transformer can increase and decrease it given power with certain loads to try to match it.
i would only be concern with electrical dampening with tubes and op-amps. with discrete solid state builds not much of an issue really. you should be more concern on it's maximum output voltage at it's given output impedance.

 

 

[khaos974]

The low impedance issue, as far as frequency response is concerned is mostly a problem for balanced armatures, for example the the Shure SE535 measures 40 ohms at 1500 Hz and 10 ohms at 6000 Hz, with a 50 ohms Zoutput, that's 8.5 dB of difference, which would be very easily noticeable.

 

[mikeaj]

As a complete non-expert in this field, I agree that your reasoning makes sense.  Headphones are probably more mechanically than electrically damped compared to speakers (not to mention the mass being much less as you say), and if people think 1/8th or 1/10th ratio is fine for speakers, then you probably don't need that much for headphones.
 
I don't think there are that many people with high-Z amps complaining excessively about those Audio-Technicas, Grados, or HiFiMAN planar magnetics, many of which have relatively low impedance but relatively flat impedance over frequency curves.
 
Pre-built O2 is $95 with batteries, no enclosure (default one is about $15 including shipping), no AC transformer (transformer is about $5 + shipping), from JDS Labs web store, so a bit under $150 now.  But yeah, that's still relatively not super-cheap.  FiiO E11 would be more interesting, but it cannot operate while being charged.
 
Cheapest with enough voltage for most headphones is probably some kind of dual-battery barebones CMoy on eBay, maybe in the range of $40.  But I'll take no claim of liability if one battery gets disconnected or dies, and you get massive DC on the output, frying your headphones. 

 
If just HD 650, then I would also suspect that the Behringer MicroMon is powerful enough.  But such a headphones monitoring amp (with emphasis on mic inputs, no less) is definitely not designed for high fidelity, so you may or may not get "distortion below audible levels."

 

[SanjiWatsuki]

 
This is most definitely an issue. I'd never match a high Z amp to a balanced armature -- things definitely get dicey when your damping factor is under 1. 
 
Quote:

The low impedance issue, as far as frequency response is concerned is mostly a problem for balanced armatures, for example the the Shure SE535 measures 40 ohms at 1500 Hz and 10 ohms at 6000 Hz, with a 50 ohms Zoutput, that's 8.5 dB of difference, which would be very easily noticeable.

I agree that the CMoy is a great value. My main worry is just QC when it comes from eBay and just the hassle of switching out batteries when using it. Also, if you use two sets of recharging batteries to solve this, they'll put out a lower voltage compared to the normal alkaline batteries which can reduce the effectiveness of the CMoy, but for high impedance loads it'll still be beast. The CMoy, in all honesty, though, still wouldn't be good for low impedance headphones due to voltage reasons, rather than impedance.  

 
Quote:

As a complete non-expert in this field, I agree that your reasoning makes sense.  Headphones are probably more mechanically than electrically damped compared to speakers (not to mention the mass being much less as you say), and if people think 1/8th or 1/10th ratio is fine for speakers, then you probably don't need that much for headphones.
 
I don't think there are that many people with high-Z amps complaining excessively about those Audio-Technicas, Grados, or HiFiMAN planar magnetics, many of which have relatively low impedance but relatively flat impedance over frequency curves.
 
Pre-built O2 is $95 with batteries, no enclosure (default one is about $15 including shipping), no AC transformer (transformer is about $5 + shipping), from JDS Labs web store, so a bit under $150 now.  But yeah, that's still relatively not super-cheap.  FiiO E11 would be more interesting, but it cannot operate while being charged.
 
Cheapest with enough voltage for most headphones is probably some kind of dual-battery barebones CMoy on eBay, maybe in the range of $40.  But I'll take no claim of liability if one battery gets disconnected or dies, and you get massive DC on the output, frying your headphones. 

 
If just HD 650, then I would also suspect that the Behringer MicroMon is powerful enough.  But such a headphones monitoring amp (with emphasis on mic inputs, no less) is definitely not designed for high fidelity, so you may or may not get "distortion below audible levels."

 

 

[nikongod]

Quote:

 
This is most definitely an issue. I'd never match a high Z amp to a balanced armature -- things definitely get dicey when your damping factor is under 1. 
 

 
Irony, sweet irony....
What about the Etymotic earphones? They ALL have resistors in the cables to alter the damping factor, and none of them have a damping factor higher than one. Check it out, the actual drivers have a ~4.5ohm DCR, and ~26ohms more in the cable... much less than 1. For a VERy long time the ETY ER4 was the best IEM available. Depending what you are looking for it is still a very very strong contender in the IEM field... with no reasonable way to get the damping factor higher than even ~1/6. I guess you could recable them without resistors, but why when they have a sound so many like. 
 
Damping factor matters on multi-way speakers and headphones not because of electrical damping on the drivers themselves*, but because crossovers only work correctly with a specific source impedance. Miss-matched up crossover points trump any sound difference as a result of electrical damping on the drivers, so a standard needs to be agreed upon to make sure that the output impedance of the amplifier does not interfere. There is absolutely no reason that a passive crossover will not work with an amp with a fairly high output impedance, provided the crossover is designed to work with that impedance. 
 
*regarding the damping factor on the drivers, please consider the output impedance of passive crossovers. When you include them it becomes very apparent that the damping factor on the actual drivers is never more than 10 no mater how low the output impedance of the amplifier is. 

 

[SanjiWatsuki]

Very cool. I will admit, I'm definitely not a sound engineer and I'm pretty new to the whole headphone field, but I'm trying to learn and put the pieces together. Thanks for that knowledge and correcting my mistake, I was mistaken on the effect of source impedance on multi-driver balanced armature earphones. I suppose a better revision of this topic would be the effects of source impedance on dynamic-driver headphones, because planar magnetics don't suffer from frequency response deviations and balanced armatures are a whole different monster when it comes to multiple drivers.
Quote:

 
Irony, sweet irony....
What about the Etymotic earphones? They ALL have resistors in the cables to alter the damping factor, and none of them have a damping factor higher than one. Check it out, the actual drivers have a ~4.5ohm DCR, and ~26ohms more in the cable... much less than 1. For a VERy long time the ETY ER4 was the best IEM available. Depending what you are looking for it is still a very very strong contender in the IEM field... with no reasonable way to get the damping factor higher than even ~1/6. I guess you could recable them without resistors, but why when they have a sound so many like. 
 
Damping factor matters on multi-way speakers and headphones not because of electrical damping on the drivers themselves*, but because crossovers only work correctly with a specific source impedance. Miss-matched up crossover points trump any sound difference as a result of electrical damping on the drivers, so a standard needs to be agreed upon to make sure that the output impedance of the amplifier does not interfere. There is absolutely no reason that a passive crossover will not work with an amp with a fairly high output impedance, provided the crossover is designed to work with that impedance. 
 
*regarding the damping factor on the drivers, please consider the output impedance of passive crossovers. When you include them it becomes very apparent that the damping factor on the actual drivers is never more than 10 no mater how low the output impedance of the amplifier is. 

 

 

[Chris J]

Quote:

Hello, Head-Fi Sound Science forum. I've been doing a lot of research on amplifiers and damping factor and this question has very much bugged me. I'm wondering if you guys think my logic is solid. 
 
Allow me to say first off that there is no room to doubt that low impedance headphones/earphones, such as balanced IEMs or highly efficient portable headphones, will be greatly affected by high source impedance. Their frequency response will be all messed up, their sound decay time might double in length making their bass muddy and "loose." What I'm concerned with, however, is the effect of a high impedance headphone out (~50 ohms, a number found often in low cost headphone amps and the headphone out of professional audio equipment) on the sound of higher impedance headphones, anything from 50 to 600.
 
To start, let's focus on the frequency response aspect. This part is relatively easy if there is a published impedance chart for the headphones. We can take the maximum impedance, add in the source impedance, and calculate the change in dB and do the sound for the lowest impedance. Using a combination of these two values we can determine a range that the sound changed based upon the source impedance mathematically. Here's an example:
 
Using Tyll's chart for the Grado SR60i, we'll measure the dB differences in this low 32ohm impedance headphone when fed a 50ohm source impedance amplifier. The lowest impedance appears to be 32 and the highest appears to be 42. We will assume a 1 volt source.
Voltage at 32 ohm: 32 / (32 + 50) = .39
Voltage at 42 ohm: 42 / (42 + 50) = .457
Frequency response deviation: 20 * log (.457/.39) = 1.38dB
 
So, at one volt, we experience only a 1.38dB variation in sound -- basically, barely audible for this highly efficient headphone that doesn't require an amp. Results will, of course, differ headphone to headphone. Furthermore, there can be some massive loss in voltage if the headphone is of a lower impedance than the amp, but that's very difficult to predict how much will be lost. The gist of what I'm saying is that, if you can calculate a small difference in the frequency response, this aspect of headphone impedance can be ignored.
 
--
 
The next important aspect of output impedance is the electrical damping factor. Think of it as the amount of control the amplifier has on the driver. The lower the damping factor, the more the driver will vibrate after it isn't supposed to vibrate. The question is how much damping factor is needed and how much does it affect the sound quality?
 
I found this study on the effect of damping factor on speakers for this aspect. Granted, these are speakers and not headphones but the general principles apply. The main thing in my mind when I was reading this was that, because of the lower mass of headphone drivers, the less of an effect electrical damping will have on it. The driver has less mass moving and, therefore, will be less affected by damping factor. I feel Tyll's graphs for him testing the DT 48e at his normal testing impedance and then again with a 120 ohm source impedance (damping factor of .208) backs me up with this idea. The differences between the impulse decay time and the difference in time for it to make the sine waves changed in what appears to be an insignificant time. Furthermore, just the overall impulse response time for headphones just seems much lower than the decay time for speakers. Granted, these are different testing mechanisms and the numbers are not completely compatible, but I think it conveys the gist of the idea. Therefore, we can assume the differences in decay time for speakers is of some level of magnitude greater than it would be for speakers.
 
The study I linked came to the conclusion that any damping factor over 10 could safely be said to have no audible differences. Given that the decay differences is some degree of magnitude greater than it would be for speakers, it seems logical that a damping factor closer to the range of 1 to 3 would safely result in non-audible differences due to the amplifier's control over the driver. If we take the extreme and divide the decay time of the speaker by a Tyll impulse response time and multiply it by the damping factor of 10, the number would be significantly under 1, but that doesn't seem to be a logical step to take.
 
--
 
Heading onto the further implications of these conclusions, let's observe if the HD 650 could be capably powered by a $19 Behringer Micromon MA400 headphone amp. We will try to power it to 110 peak SPL ( Antilog ( ( 110 – 103) / 20 )  = 2.2 Vrms ). The Behringer spec sheet says it has . We calculate Vrms from dBu by antilog (dBu / 20) * .775 = V. Given that the dBu is +10, we can find the rated output to be 2.45Vrms -- more than enough to power the HD 650 to 110 peak SPL! Next, we'll calculate the frequency response changes.
 
From Tyll's charts for the HD 650, we know the lowest impedance to be around 300ohm and the highest to be around 520ohm.
Voltage at 300 ohm: 300 / (300 + 30) = .91
Voltage at 520 ohm: 520 / (520 + 30) = .945
Frequency response deviation: 20 * log (.945/.91) = 0.27dB
 
There is an inaudible frequency response change at 0.27dB.
 
Finally, the damping factor of the headphone is 10 -- effectively inaudible. Assuming the Behringer Micromon MA400 amp has distortion below audible levels, it is a  $20 desktop amp which should be able to power the Sennheiser HD650.
 
Is this a logical conclusion? Just wanted to make sure I wasn't going crazy.
 

Basically, your logic looks pretty sound.
I don't think you are going crazy, but for a professional opinion I would go see a registered psychologist.
I like your conclusions on damping factor.
Makes sense, headphones don't have a lot of mass relative to loudspeakers.
 
In my experience (and this is completely subjective, I didn't measure anything) low damping factor does make for bloomy bass, but this is only based on me plugging in my 62 ohm AKG Q701s into the headphone jack on my Bryston 2B-LP power amp. The 2B-LP headphone jack has 150 ohm resistors in the path.  I thought the bass was a lot boomier and fuller thru the Bryston than thru my Matrix M Stage which has an output impedance of 5 ohms (or so the manual says).
 

 

[Chris J]

Quote:

 
Irony, sweet irony....
What about the Etymotic earphones? They ALL have resistors in the cables to alter the damping factor, and none of them have a damping factor higher than one. Check it out, the actual drivers have a ~4.5ohm DCR, and ~26ohms more in the cable... much less than 1. For a VERy long time the ETY ER4 was the best IEM available. Depending what you are looking for it is still a very very strong contender in the IEM field... with no reasonable way to get the damping factor higher than even ~1/6. I guess you could recable them without resistors, but why when they have a sound so many like. 
 
Damping factor matters on multi-way speakers and headphones not because of electrical damping on the drivers themselves*, but because crossovers only work correctly with a specific source impedance. Miss-matched up crossover points trump any sound difference as a result of electrical damping on the drivers, so a standard needs to be agreed upon to make sure that the output impedance of the amplifier does not interfere. There is absolutely no reason that a passive crossover will not work with an amp with a fairly high output impedance, provided the crossover is designed to work with that impedance. 
 
*regarding the damping factor on the drivers, please consider the output impedance of passive crossovers. When you include them it becomes very apparent that the damping factor on the actual drivers is never more than 10 no mater how low the output impedance of the amplifier is. 

Interesting stuff...........
Just my opinion here:
For Etymotic headphones the 26 ohms in the cable assembly is deliberately designed in.
I suspect they can do this because the ETY ER4 driver has a very high efficiency so you can afford to loose a lot of voltage drop across the cable.
I would also suspect that very few headphone amplifiers can safely drive a 4.5 ohm impedance, i.e. it would look like a short circuit to a lot of headphone amplifiers.
And I would also guess that the ETY ER4 driver has a flat impedance across the audio bandwidth.
 
For for crossovers, they are generally designed to work with an almost zero output impedance source.
This is probably one of the causes of the colouration of vacuum tube power amps. 
But I agree that they would work with a specific high output impedance source if they were designed to work with that specific source impedance.
Makes sense that the crossover would be detrimental to the damping factor of a loudspeaker system.
 
Mr. Rex there are a few errors in your post, if you will allow me.............
 
"........speakers never have any issues cause speaker output impedances are always close to 0ohms(for well built solid state of course) and dynamic driver vary with frequency. i usually just go by the 1/8 rule most of the time. like 1/8 of 600ohms is 75 and so forth.............
 
I asume you mean audio power amplifier output impedances are close to zero so I basically agree with you.

"i have used headphones before with very high output impedances of 680 ohms but never ran issues with low impedance headphones due to the ability of the power transformer matching the impedance of the headphone. tubes and op-amps are different. while tubes highly rely on output power transformers to give their given output impedance, and while op-amps has a fix output impedance as well. a discrete solid state amp with a large(or some cases dual) transformer(s) not only acts by blocking EMI and giving the amp it's maximum voltage output but matches impedances as well,since the transformer can increase and decrease it given power with certain loads to try to match it."
 
 
The power transformer is not used to match the impedance of the headphone, the power transformer is part of the power supply circuit and is used to convert 120 Vac into a lower voltage for the headphone amplifier power supply.
In a tube amp with an output transfomer, the output transformer is used to decrease the output voltage of the output tubes, increase the output current of the output tubes and decrease the output impedance of the amp. So in this case the output impedance is strongly dependent on the characteristics of the output transformer.


"i would only be concern with electrical dampening with tubes and op-amps. with discrete solid state builds not much of an issue really. you should be more concern on it's maximum output voltage at it's given output impedance."
 
Op Amps and discrete circuits basically follow the same rules, the output impedance is set by two things: the output impedance of the output transistors and whatever value resistor they put on the output of the op amp or discrete solid state circuit.
 
 
 

 

[kingpage]

Quote:

As for buying a low impedance headphone amp with high output, they exist but they are even more expensive than buying a pre-built DIY option. Virtually every single under $100 commercial headphone amp with more than 2V output an output impedance of 50 to 100. Beyond the Fiio E10 (which really does appear to be a good deal with its Wolfson DAC), which likely has the same 10 ohm impedance of its E11 brother and probably caps out under 3V, I don't think any budget high-power low-impedance amps out of DIY really exist. 

I just needed to correct some mistakes here. E9 has an impedance of 10ohm (43 for the small jack), not E11. E11 is tested to be 0.5ohm and E10 is stated (by FiiO) to be 0.3ohm but yet to be tested by you-know-who. So for now, basically except E9, all FiiO amps have low output impedance.
 

 

[SanjiWatsuki]

I corrected it, thanks!
 
Quote:

I just needed to correct some mistakes here. E9 has an impedance of 10ohm (43 for the small jack), not E11. E11 is tested to be 0.5ohm and E10 is stated (by FiiO) to be 0.3ohm but yet to be tested by you-know-who. So for now, basically except E9, all FiiO amps have low output impedance.
 

 

 

[markkr]

So if I'm understanding this correctly, using specific examples
 
Centrance DACmini (10ohm) -> Grado (32ohm) = bad
Centrance DACmini (1ohm) -> Grado (32ohm) = good
 
Centrance DACmini (10ohm) -> Beyer DT880 (600ohm) = good
Centrance DACmini (1ohm) -> Beyer DT880 (600ohm) = bad
 
Is this correct?
 
Thanks