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Topic: Help with headphone compatibility (Read 11017 times) previous topic - next topic
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Help with headphone compatibility

Hi

I’ve ordered an O2 amp with ODAC which I should get in a couple of weeks. This is the open source amp and DAC by NWAVGuy who recommends this forum for objective advice.

I already own Sennheiser HD650’s which this amp will have no problem driving looking at the specs and reading user reports. I want to know your thoughts on this amp’s abilities to drive two other headphones I am interested in to experience their different sound signatures.

Firstly the AKG K701 – I keep reading this headphone is hard to drive but the specs I’ve found don’t seem to bear this out. The impedance is 62 ohms which is quite low compared to the HD650 at 300ohms. The sensitivity is 105 db per volt which is similar to the HD650’s 103db per volt and equates to about 97db per milliwatt. I don’t understand why people are saying the AKG’s are more diicult to drive than the Sennheisers as these specs suggest it should be the other way round. Has anyone got any experience with this headphone and the O2 amp?

The second headphone I am interested in is the Beyerdynamic DT880 600ohm. NWAVGuy says this needs at least 5 volts to drive and the O2 can put a maximum of 7 volts into 600ohms. It looks like this is ample to handle this headphone on paper but I want to know if anyone has any experience of actually using this combination rather than relying on hearsay. What I don’t want is to regularly run the amp right up to its limits in case it gets a bit ragged. The music (and games in particular) I own vary quite considerably in volume hence amp requirements. Can anyone with experience confirm whether this amp has enough power for this amp in practical use?

My final question relates to the Beyerdynamic DT880 above. I’m drawn to the 600ohm version as the reports I’ve read suggest this sounds the best and has the best treble. There is also a 250ohm version (the original impedance I think) which is much easier to drive. Does anyone have any direct experience of the actual sonic difference between the 250ohm and 600ohm versions? If it is marginal then the 250ohm seems a safer bet as the O2 should handle this more easily.

Thanks in advance

Mag

Help with headphone compatibility

Reply #1
Hi

I’ve ordered an O2 amp with ODAC which I should get in a couple of weeks. This is the open source amp and DAC by NWAVGuy who recommends this forum for objective advice.

I already own Sennheiser HD650’s which this amp will have no problem driving looking at the specs and reading user reports. I want to know your thoughts on this amp’s abilities to drive two other headphones I am interested in to experience their different sound signatures.

Firstly the AKG K701 – I keep reading this headphone is hard to drive but the specs I’ve found don’t seem to bear this out. The impedance is 62 ohms which is quite low compared to the HD650 at 300ohms. The sensitivity is 105 db per volt which is similar to the HD650’s 103db per volt and equates to about 97db per milliwatt. I don’t understand why people are saying the AKG’s are more diicult to drive than the Sennheisers as these specs suggest it should be the other way round. Has anyone got any experience with this headphone and the O2 amp?

The second headphone I am interested in is the Beyerdynamic DT880 600ohm. NWAVGuy says this needs at least 5 volts to drive and the O2 can put a maximum of 7 volts into 600ohms. It looks like this is ample to handle this headphone on paper but I want to know if anyone has any experience of actually using this combination rather than relying on hearsay. What I don’t want is to regularly run the amp right up to its limits in case it gets a bit ragged. The music (and games in particular) I own vary quite considerably in volume hence amp requirements. Can anyone with experience confirm whether this amp has enough power for this amp in practical use?

My final question relates to the Beyerdynamic DT880 above. I’m drawn to the 600ohm version as the reports I’ve read suggest this sounds the best and has the best treble. There is also a 250ohm version (the original impedance I think) which is much easier to drive. Does anyone have any direct experience of the actual sonic difference between the 250ohm and 600ohm versions? If it is marginal then the 250ohm seems a safer bet as the O2 should handle this more easily.


As long as you keep high linearity, high NFB amps like the 02 from clipping, there will be no audible distortion.

So this statement: "That I don’t want is to regularly run the amp right up to its limits in case it gets a bit ragged."  we be more about paranoia than actual SQ problems as long as clipping is not involved.

OTOH, I find 7 volts peak output into high imepdance loads to be a bit modest.

The O2 amp itself seems like it could be hacked to produce more power by simply raising the power supply voltage and using IC regulators with higher voltages (e.g. 18 bolts) than the modest 12 volt units in the original design.

Help with headphone compatibility

Reply #2
Firstly the AKG K701 – I keep reading this headphone is hard to drive but the specs I’ve found don’t seem to bear this out. The impedance is 62 ohms which is quite low compared to the HD650 at 300ohms. The sensitivity is 105 db per volt which is similar to the HD650’s 103db per volt and equates to about 97db per milliwatt. I don’t understand why people are saying the AKG’s are more diicult to drive than the Sennheisers as these specs suggest it should be the other way round.


Your calculation is incorrect: the AKG K701s are indeed 105 dB/V, but you have to take their impedance into account (62?):
dBV - (10 * log10(1000/Z)) = 105 - (10 * log10(1000/62)) = 93 dB/mW

The Sennheiser HD 650s are 103 dB/V, 300? = 98 dB/mW
The Beyerdynamic DT 880s are (reportedly) 96 dB/mW.

NwAvGuy says the O2 can drive all those cans just fine.

Help with headphone compatibility

Reply #3
While the NJM4556 is specified for supplies up to +/-18V, it would be increasingly unhappy driving low-impedance loads, potentially becoming uncomfortably warm.

Really, 7 Vrms is just fine for most anything short of K240M/DFs. It still is good for 110+ dB with DT880-600s.

Incidentally, K701s measure about 100 dB / 1 V, so they are in fact a little quieter than the usual Senns, at lower impedance, which makes them harder to drive.

Oh, and when used with the ODAC, the standard 2.5x low gain of the O2 would be fine. That would give you a nominal 5 Vrms output, with a bit of headroom for intersample-overs.

Help with headphone compatibility

Reply #4
When desired atainable SPL is 115dB (peaks for dynamic range taken into account, you wouldn't want to listen to an average volume this high) you get:

antilog((115-96)/10)= 79.43 mW
The O2 can deliver 88 mW @ 600 Ω, so you're good.

Help with headphone compatibility

Reply #5
Firstly the AKG K701 – I keep reading this headphone is hard to drive but the specs I’ve found don’t seem to bear this out. The impedance is 62 ohms which is quite low compared to the HD650 at 300ohms. The sensitivity is 105 db per volt which is similar to the HD650’s 103db per volt and equates to about 97db per milliwatt. I don’t understand why people are saying the AKG’s are more diicult to drive than the Sennheisers as these specs suggest it should be the other way round.


Your calculation is incorrect: the AKG K701s are indeed 105 dB/V, but you have to take their impedance into account (62?):
dBV - (10 * log10(1000/Z)) = 105 - (10 * log10(1000/62)) = 93 dB/mW

The Sennheiser HD 650s are 103 dB/V, 300? = 98 dB/mW
The Beyerdynamic DT 880s are (reportedly) 96 dB/mW.

NwAvGuy says the O2 can drive all those cans just fine.


Help with headphone compatibility

Reply #6
Firstly the AKG K701 – I keep reading this headphone is hard to drive but the specs I’ve found don’t seem to bear this out. The impedance is 62 ohms which is quite low compared to the HD650 at 300ohms. The sensitivity is 105 db per volt which is similar to the HD650’s 103db per volt and equates to about 97db per milliwatt. I don’t understand why people are saying the AKG’s are more diicult to drive than the Sennheisers as these specs suggest it should be the other way round.


Your calculation is incorrect: the AKG K701s are indeed 105 dB/V, but you have to take their impedance into account (62?):
dBV - (10 * log10(1000/Z)) = 105 - (10 * log10(1000/62)) = 93 dB/mW

The Sennheiser HD 650s are 103 dB/V, 300? = 98 dB/mW
The Beyerdynamic DT 880s are (reportedly) 96 dB/mW.

NwAvGuy says the O2 can drive all those cans just fine.

Thanks for reply. I didn't know impedance affected the sensitivity calculation. I know HD600's (and presumably HD650's) are 97 db/mW so I thought I could just substitute this for the AKG's. That makes more sense now as 93 is considerably lower.

Thanks again

Mag

Help with headphone compatibility

Reply #7
Hi

Thanks for all your replies chaps - very helpful. Has anyone got any thoughts on sonic differences between Beyer DT880  600ohm and 250ohm versions. I've ordered a pair of AKG K701's so it is just the Beyers I need to make a decision over.

Thanks in advance

Mag

Help with headphone compatibility

Reply #8
Quote
Has anyone got any thoughts on sonic differences between Beyer DT880 600ohm and 250ohm versions.
Of course, the 250 Ohm version should be slightly louder (with the same voltage).    Otherwise if there are any audible differences, I would assume the differences are subtle and it would come down to personal preference.  I also assume the frequency response specs are the same? 

Quote
Thanks for reply. I didn't know impedance affected the sensitivity calculation.
It usually doesn't...    It depends on how sensitivity is defined.    If you see XdB @ Y Volts, impedance is not a factor as long as you know the output voltage rating from the amp and that it's capable of driving the headphone's impedance.    If you see XdB @ Y mW (efficiency) you'll need to know the impedance to calculate the required voltage.

Most amplifiers are "constant voltage" devices.    That doesn't really mean the voltage is constant, since it obviously varies with the music and the volume control.  It means that the internal source impedance is low, so the output voltage doesn't vary (much) when load impedance varies (as long as the load impedance is within spec).

If you cut the impedance in half and keep the voltage constant, you get twice the power, and all else being equal,  twice the acoustic power (+3dB more volume).    In cases where a manufacturer offers the same model in two different impedances, everything else is nearly equal and the headphones will have nearly the same efficiency dB/mW, and the lower impedance headphone will have higher sensitivity (dB/V). 

Since it takes more voltage to get the same power (mW) out of a higher impedance headphone, these higher impedance headphones typically require higher voltage, and someone might say that a 250 or 600 Ohm headphone is "hard to drive", compared to a 32 Ohm headphone.

If you have a poorly designed headphone amp (or a soundcard that's not optimized for driving headphones), it may very from the "constant voltage" ideal.    Since the impedance of all headphones varies over the frequency range, the frequency response of these headphone amps can be different with different headphones.        Or if there is an output capacitor, and it's on the small size, you can lose bass on low impedance headphones.   

These interactions (that only occur with badly designed headphone amps) are minimized  (or virtually eliminated) with higher impedance headphones (250 or 600 Ohms).  But of course, the reduced sensitivity often means that the cheap headphone amp can't put out the voltage needed for the desired volume.

Help with headphone compatibility

Reply #9
Quote
Has anyone got any thoughts on sonic differences between Beyer DT880 600ohm and 250ohm versions.
Of course, the 250 Ohm version should be slightly louder (with the same voltage).    Otherwise if there are any audible differences, I would assume the differences are subtle and it would come down to personal preference.  I also assume the frequency response specs are the same? 

Quote
Thanks for reply. I didn't know impedance affected the sensitivity calculation.
It usually doesn't...    It depends on how sensitivity is defined.    If you see XdB @ Y Volts, impedance is not a factor as long as you know the output voltage rating from the amp and that it's capable of driving the headphone's impedance.    If you see XdB @ Y mW (efficiency) you'll need to know the impedance to calculate the required voltage.

Most amplifiers are "constant voltage" devices.    That doesn't really mean the voltage is constant, since it obviously varies with the music and the volume control.  It means that the internal source impedance is low, so the output voltage doesn't vary (much) when load impedance varies (as long as the load impedance is within spec).

If you cut the impedance in half and keep the voltage constant, you get twice the power, and all else being equal,  twice the acoustic power (+3dB more volume).    In cases where a manufacturer offers the same model in two different impedances, everything else is nearly equal and the headphones will have nearly the same efficiency dB/mW, and the lower impedance headphone will have higher sensitivity (dB/V). 

Since it takes more voltage to get the same power (mW) out of a higher impedance headphone, these higher impedance headphones typically require higher voltage, and someone might say that a 250 or 600 Ohm headphone is "hard to drive", compared to a 32 Ohm headphone.

If you have a poorly designed headphone amp (or a soundcard that's not optimized for driving headphones), it may very from the "constant voltage" ideal.    Since the impedance of all headphones varies over the frequency range, the frequency response of these headphone amps can be different with different headphones.        Or if there is an output capacitor, and it's on the small size, you can lose bass on low impedance headphones.   

These interactions (that only occur with badly designed headphone amps) are minimized  (or virtually eliminated) with higher impedance headphones (250 or 600 Ohms).  But of course, the reduced sensitivity often means that the cheap headphone amp can't put out the voltage needed for the desired volume.


Thanks for your reply.

Can I just clarify something? When a headphone is described as say 97 dB/V is this correctly described as a measure of its sensitivity? When a headphone is described as say 100 dB/mW is this correctly described as a measure of its efficiency?

I think I was incorrect in assuming both dB/V and dB/mW were measures of sensitivity.

Thanks in advance

Mag


Help with headphone compatibility

Reply #10
Both are measures of efficiency/sensitivity, and their values are related by the impedance.

Help with headphone compatibility

Reply #11
As I read this thread I'll add another question - the impedances of headphones given by manufacturers are 'nominal' numbers. The impedance of a transducer varies depending on the frequency of a sound it has to generate, Beyer T1's impedance at the bass frequencies, centered on 80-90Hz, is not 600 Ohm but around 1430 Ohm.- www.innerfidelity.com/images/BeyerdynamicT1SN3964.pdf -
An amplifier's voltage that manages to deal with 600 Ohm impedance might not be enough for 1430 Ohm impedance barrier. So what would be the required voltage to make T1 sound even across all frequencies ? What is the voltage needed to drive headphones with 1430 Ohm peak ?

Help with headphone compatibility

Reply #12
As I read this thread I'll add another question - the impedances of headphones given by manufacturers are 'nominal' numbers. The impedance of a transducer varies depending on the frequency of a sound it has to generate, Beyer T1's impedance at the bass frequencies, centered on 80-90Hz, is not 600 Ohm but around 1430 Ohm.- www.innerfidelity.com/images/BeyerdynamicT1SN3964.pdf -
An amplifier's voltage that manages to deal with 600 Ohm impedance might not be enough for 1430 Ohm impedance barrier. So what would be the required voltage to make T1 sound even across all frequencies ? What is the voltage needed to drive headphones with 1430 Ohm peak ?


The evidence above shows that the increase in impedance is almost precisely matched by an increase in efficiency resulting in flat response.

This means that dealing with the higher impedance isn't causing a problem in the test.

All other things being equal, higher impedances are easier to drive.  But, all things aren't always equal.

High impedance is only suggestive of a problem when the headphone is speced in terms of SPL and power.  The higher impedance means that more voltage needs to be provided for a given SPL which may be difficult for most portable digital players to provide since they are usually voltage limited.

If you have a portable player that struggles to provide enough voltage to drive your high impedance headphones all you have to do is obtain a headphone amp that provides relatively high voltage with very low noise and distortion.

A unit such as the ca. $40 Topping NX-1 will solve the problem in almost every case. If its claimed 22 volt output voltage is representative, its probably more competent than many far more expensive solutions.

Help with headphone compatibility

Reply #13
A unit such as the ca. $40 Topping NX-1 will solve the problem in almost every case. If its claimed 22 volt output voltage is representative, its probably more competent than many far more expensive solutions.


Huh? It's rated at 8.2Vpp…

Help with headphone compatibility

Reply #14
As I read this thread I'll add another question - the impedances of headphones given by manufacturers are 'nominal' numbers. The impedance of a transducer varies depending on the frequency of a sound it has to generate, Beyer T1's impedance at the bass frequencies, centered on 80-90Hz, is not 600 Ohm but around 1430 Ohm.- www.innerfidelity.com/images/BeyerdynamicT1SN3964.pdf -
An amplifier's voltage that manages to deal with 600 Ohm impedance might not be enough for 1430 Ohm impedance barrier. So what would be the required voltage to make T1 sound even across all frequencies ? What is the voltage needed to drive headphones with 1430 Ohm peak ?


The evidence above shows that the increase in impedance is almost precisely matched by an increase in efficiency resulting in flat response.

This means that dealing with the higher impedance isn't causing a problem in the test.

All other things being equal, higher impedances are easier to drive.  But, all things aren't always equal.

High impedance is only suggestive of a problem when the headphone is speced in terms of SPL and power.  The higher impedance means that more voltage needs to be provided for a given SPL which may be difficult for most portable digital players to provide since they are usually voltage limited.

If you have a portable player that struggles to provide enough voltage to drive your high impedance headphones all you have to do is obtain a headphone amp that provides relatively high voltage with very low noise and distortion.

A unit such as the ca. $40 Topping NX-1 will solve the problem in almost every case. If its claimed 22 volt output voltage is representative, its probably more competent than many far more expensive solutions.



A transportable amp manufacturer sent me an email that 12V driving voltage is enough for Beyerdynamic T1. I am trying to make him modify the amp for T1 and raise the voltage output from 5V to something like 15V. I am not sure 12 V is enough.

Help with headphone compatibility

Reply #15
A unit such as the ca. $40 Topping NX-1 will solve the problem in almost every case. If its claimed 22 volt output voltage is representative, its probably more competent than many far more expensive solutions.


Huh? It's rated at 8.2Vpp…



My error.  I don't recall where I saw the 22 volt number. 8.2 v p-p is almost 3 volts RMS

The O2 is rated indirectly. It works out as follows:
Code: [Select]
Power, W      Impedance, ohms                   Voltage
0.633                   33                     4.570448556
0.355                  150                     7.29725976
0.088                  600                     7.26636085



Help with headphone compatibility

Reply #16
A transportable amp manufacturer sent me an email that 12V driving voltage is enough for Beyerdynamic T1. I am trying to make him modify the amp for T1 and raise the voltage output from 5V to something like 15V. I am not sure 12 V is enough.


Beyer by implication says that 9.5 volts RMS is their recommended maximum.

at their recommended 300 mw max, the calculated SPL is about 126 dB SPL - definite ear bleed territory.

Help with headphone compatibility

Reply #17
I also have the HD 650 and K702 (same as K701, but with the detachable cable), and I also have the O2+ODAC. This might sound subjective, but I don't hear any distortion at all. I pretty much love what I hear.

Help with headphone compatibility

Reply #18
A transportable amp manufacturer sent me an email that 12V driving voltage is enough for Beyerdynamic T1. I am trying to make him modify the amp for T1 and raise the voltage output from 5V to something like 15V. I am not sure 12 V is enough.


Beyer by implication says that 9.5 volts RMS is their recommended maximum.

at their recommended 300 mw max, the calculated SPL is about 126 dB SPL - definite ear bleed territory.


It is all about the amp having enough 'headroom' so as not straining to work at the limit of its specifications.
Thanks for the help.

Help with headphone compatibility

Reply #19
It is all about the amp having enough 'headroom' so as not straining to work at the limit of its specifications.


Amps don't "strain" as such - they just clip if you exceed the amplitude they can't handle.

Help with headphone compatibility

Reply #20
It is all about the amp having enough 'headroom' so as not straining to work at the limit of its specifications.



"Straining to work at the limit of its specifications"  is yet another an audiophile myth.

SS amplifiers have uniform to barely increasing or even decreasing nonlinearity right up to the point where they clip.  Any modern amplifier has at least 10 times less distortion than is audible, at any power level right up to just under clipping  under the most ideal of circumstances that are conceivable. With real world music, the safety margin is at least 10 times greater than that.

There may have been a time in the early 50s or earlier when the highly underdeveloped tubed power amplifiers of the day may have had so much distortion that they did sound strained at reasonable listening levels and had marginal enough power capabilities that the now myth may have had some reality to it.

Bottom line is that if you are listening with music, even a little clipping can slip right by the ears without being perceived.

On balance, modern portable digital music players can be marginal enough (in some countries by law) that some listeners may push them into audible clipping or simply not be able to drive certain headphones to sufficient SPLs for every listener to obtain what he perceives to obtain a balanced, dynamic sonic presentation.  But, this is a different problem than "Straining to work at the limit of its specifications".

It is possible to design the gain staging of a music player with a digital source so that it is impossible to make it clip even in the slightest.

Sighted evaluations will and have confirmed any myth that the human mind can conceive of including this one.