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Driving headphones properly

NDRQ

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What is important to drive headphone properly?
In many other forums i read that not just the voltage but also the current is very important and some headphones like high current output, but usually most amplifier only strong with voltage and thats why many hard to drive phone sounds bad from most amplifier even though they measure well.
So what is truth behind these things?

I dont know too much about this, really thank you for any comment.
 

sergeauckland

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Headphones, like loudspeakers, have an impedance that varies with frequency, consequently they should be driven from as low an output impedance as practicable, certainly no more than 10% of their minimum impedance, and better is 5%. After that, they need as many volts as are necessary to achieve the loudness one needs. Current needs are then a simple matter of Ohms's Law.

The old practice of having a headphone output from a power amplifier with a relatively high value resistor in series is a very poor solution, as the results will be very variable depending on the headphones. I personally use a 5532 opamp as a headphone driver as it drives my 75 ohm AKGs and 400 ohm KOSS headphones perfectly adequately with a +-15v supply, and has a satisfactorily low output impedance.

S
 
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NDRQ

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Thanks for the reply.
I know about the ohm part, the damping factor should be at least 8-10 and higher is better, but this voltage vs current thing is confusing.
 

sergeauckland

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Yes, a damping factor of 10-20 is ideal, but it needs to be based on the minimum impedance, not just the nominal. Few headphones specify that, so as high a damping factor as possible is good.

As to volts and amps, headphones specify their sensitivity in various ways, but these always come back to a certain number of volts for a certain loudness, so that's what's important. Then, the current requirement can be calculated from the volts and impedance using Ohm's Law, I=V/R.

S
 

solderdude

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Low impedance headphones can be driven with low output voltage devices.
Most phones etc. can put out max 1V.
So portable equipment works well with low impedance (and/or high efficiency) headphones.

High impedance headphones require a higher voltage.
For this you need specialized portable equipment with a higher supply voltage rails or desktop equipment.
Phones can not deliver enough voltage to play them loud.
These amps do not require high current capabilities.

a 300 Ohm headphone requires about 3.3x (SQR10) more voltage than a 30 Ohm headphone to play equally loud when the efficiency (dB/mW) is the same.
But at the same time the 300 Ohm headphones draws 3.3x less current than the 30 Ohm headphone.

High impedance headphones require a higher output voltage and draw less current.
Low impedance headphones require a lower output voltage but draw more current.

But in every case there are exceptions. There are also low impedance headphones with a low efficiency which thus require a higher voltage AND need to be able to provide more current.

So... buy a headphone amp that has enough voltage swing to be able to drive high impedance headphones loudly. But to be able to play low efficiency and low impedance headphones as well it should be able to provide enough current as well.

There are plenty of those around.
 
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NDRQ

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Thanks for the reply, it is very informative.
But how can i know what amp can provide high current and high voltage at the same time? Usually there are only watts and voltages in every specs, and even though there are many high power output amp they easily fail with hard to drive phones like Hifiman HE6.

And one more thing: What is the meaning of thephase and impedance peaks in a headphone measurement and how is that interact with the headphone amp? For example i saw headphones that have nominal 150ohm but at 100hz they have 500ohm peak.
 
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amirm

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And one more thing: What is the meaning of thephase and impedance peaks in a headphone measurement and how is that interact with the headphone amp?
Most of music energy is in bass. So only look in that region for impedance and phase response. If impedance dips low and phase goes up, that is the worst case situation, requiring even more current than would be needed. Think of phase as an additional handicap.

On your larger question, I will paraphrase Dr. Toole: if you don't know the load, you need to over-purchase your amplifier. This is why I test amps with very loud levels. If they perform there, then they are likely to perform in many cases.

That said, I really need to get an HE-6. I sent email to Hifiman and to get one on loan and they just ignored it. :( If you all see a good deal on an HE-6, please let me know and I will buy and test amps in my reviews with it.
 
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NDRQ

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Thanks for the answer, so if a headphone having higher output performance, usually also have higher current output.

I will say if i see some good deal.
 

sergeauckland

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Thanks for the answer, so if a headphone having higher output performance, usually also have higher current output.

I will say if i see some good deal.
If you mean 'if a headphone amplifier having a higher output' then yes, probably so, but voltage output and current capability are not necessarily connected. You really need to find out what the maximum voltage the headphone amp can provide, and into what minimum load. It's the load that defines the current for any particular voltage. Headphone amplifiers (and amplifiers generally) are specified in terms of volts out into a minimum load impedance, although it's confused by quoting power rather than voltage. However, as power is Volts x Current, and current is Volts/impedance, they're all related.

S
 

solderdude

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When the amp has a Wattage > 100mW in 300 Ohm it has enough output voltage to drive most high impedance headphones.
When the same amp also has a higher wattage > 0.5W in 30 Ohm it can also provide enough current.

As Amir stated, it can't hurt to have an over spec'd amp. That is unless you have high efficiency IEM's or headphones with power ratings below 50mW.
These are realy easy to damage with high powered amps. These can be driven loud from phones etc so don't need amping anyway.

Then it has to have a correct amount of gain, low distortion (< 0.01%) and a wide enough frequency range into 30 Ohm (<10Hz to >50kHz) and the looks and functionality you are looking for and is within your budget than you're good.

Sometimes it is tough to see through specs. from manufacturers

When you have found 1 or more you think suit the task and list them incl. the headphones you (plan) to use then it is easier for folks here to give recommendations.
 
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NDRQ

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Many people say that even though the K712 can be drived very loudly from almost any device, these are hard to drive headphones and the bass has no body and the sound will be uneven if the amp is not good enough. So i thought maybe this is something to do with the current, because the problem is not the loudness level.

Curently im using a Concero HD + Myryad Z40 + AKG K712 pro, and this is probably good enough, sounds nice, but maybe its not optimal and i can still improve with a better performance amp.
 

solderdude

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The K712 is not 'difficult' to drive. Regardless what many people say.
The fact that it won't do thumping bass at loud levels directly from a phone does not make it 'difficult' to drive.
An urban myth. Brought on by folks reiterating what they 'read' somewhere and perhaps finds its origin in some folks not liking how it sounds at louder levels (think 2kHz bump and relative lack of lows).
frequency-response-graph.png


It produces 105dB at 1V and the impedance is not low and far from being high as well with 60 Ohm.
You don't hear any complaints about the HD599 being 'difficult' to drive, yet it produces 106dB at 1V and is 50 Ohm.
Looking for improved performance... use EQ.
You want it louder look for an amplifier that can deliver more power in 60 Ohm.

The Myryad Z40 can easily reach 6V in 60 Ohm (0.8W) so can reach 120dB peak levels.
With DR20 recordings an average level of 100dB will make you deaf before you know it.

As the amp can drive 32 Ohm to 4V = 125mA so there is NO shortage of current nor shortage of voltage.
When you want a different sound either use EQ or look for a headphone that is better suited to your taste.
 
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Maki

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The K712 is not 'difficult' to drive. Regardless what many people say.
The fact that it won't do thumping bass at loud levels directly from a phone does not make it 'difficult' to drive.
An urban myth.

It produces 105dB at 1V and the impedance is not low and far from being high as well with 60 Ohm.
You don't hear any complaints about the HD599 being 'difficult' to drive, yet it produces 106dB at 1V and is 50 Ohm.
Looking for improved performance... use EQ.
You want it louder look for an amplifier that can deliver more power in 60 Ohm.

The Myryad Z40 can easily reach 6V in 60 Ohm (0.8W) so can reach 120dB peak levels.
With DR20 recordings an average level of 100dB will make you deaf before you know it.

As the amp can drive 32 Ohm to 4V = 125mA so there is NO shortage of current nor shortage of voltage.
When you want a different sound either use EQ or look for a headphone that is better suited to your taste.
Is the K712 more sensitive than the 701? I remember my 701 being the least sensitive headphone I had, even less sensitive than the HD600. Maybe it was just unit to unit variation or something.
 
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NDRQ

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The K712 is not 'difficult' to drive. Regardless what many people say.
The fact that it won't do thumping bass at loud levels directly from a phone does not make it 'difficult' to drive.
An urban myth. Brought on by folks reiterating what they 'read' somewhere and perhaps finds its origin in some folks not liking how it sounds at louder levels (think 2kHz bump and relative lack of lows).
frequency-response-graph.png


It produces 105dB at 1V and the impedance is not low and far from being high as well with 60 Ohm.
You don't hear any complaints about the HD599 being 'difficult' to drive, yet it produces 106dB at 1V and is 50 Ohm.
Looking for improved performance... use EQ.
You want it louder look for an amplifier that can deliver more power in 60 Ohm.

The Myryad Z40 can easily reach 6V in 60 Ohm (0.8W) so can reach 120dB peak levels.
With DR20 recordings an average level of 100dB will make you deaf before you know it.

As the amp can drive 32 Ohm to 4V = 125mA so there is NO shortage of current nor shortage of voltage.
When you want a different sound either use EQ or look for a headphone that is better suited to your taste.

It was just a theoretical question, i dont have problem with the sound, and it is loud enough even at 30-40% at low gain.
I just wanted to know that maybe i dont have optimal performance with this setup.

About the hard to drive thing i didnt mean the sound level, but the sound quality. For example from my phone and PC its also very loud but much worse than my DAC+AMP setup. Altough maybe that only happens because they are poor sources..

Btw. how do you know that the Z40 can output 0.8watt at 60ohm?
In the specs only stated that 0.5w at 32ohm and 0.1w at 600ohm.
Usually the power not going lower with higher impedance?
 
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solderdude

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A question of math and knowledge about how output stages work.
At 60 Ohm the output will even be slightly higher than the given values.
The output of this amp has both a voltage and current limit.
This delivers this kind of power output


As can be seen in 60 Ohm the most power will be available. No problem for most amps that are voltage and current limited.

The K712 sounds 'worse' from the phone and PC at higher levels because the output clips.
 
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solderdude

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Is the K712 more sensitive than the 701? I remember my 701 being the least sensitive headphone I had, even less sensitive than the HD600. Maybe it was just unit to unit variation or something.

The K701 and K712 are both 105dB/V. The HD650 = 103dB/V acc. to manufacturer data.

When comparing how loud a headphone plays compared to others one really should only look at dB/V values.
The problem is there is also the, lower in value, dB/mW value.
Some manufacturers also just give the maximum SPL level (at the max rated power) and to make it worse some just give a value but do not state if it is max. SPL, dB/mW, dB/V etc. Tyll specified sensitivity by giving a voltage (and power) at 90dB SPL.
No uniformity.
I took the liberty to make a list with most known headphones (need to update it which is very time consuming) where both efficiency numbers are given.
RAA also has a practical list.
They measured values and came up with other values for the AKG and Sennheiser.

When the headphone amp has an output resistance higher than 10 Ohm the HD650 will play louder than the K7** at the same volume knob setting due to voltage division.
 
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NDRQ

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Thanks for the reply. :)

"When the headphone amp has an output resistance higher than 10 Ohm the HD650 will play louder than the K7** at the same volume knob setting due to voltage division. "

What is the exact math behind this?

I checked your link and based on that, maybe not totally a myth the "hard to drive K712" , because they need much higher voltage than 95% of the listed headphones and in the same time they also need high current. Maybe this can be challenging workload to many amp.

And another question: How is the output impedance effect the headphone frequency response?
Is there a way to estimate the effect of the output impedance to the headphone frequency response?
I mean this seems like a good way to alter frequency responses.
 
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peder2tm

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Here is the voltage division explained:
https://support.audient.com/hc/en-us/articles/205565985-Audient-Headphone-Amplifiers-Safe-SPL-Levels

One thing I miss from these discussions (and I am not sure how important it is) is the back-emf of the headphones. When combined with an high output impedance amplifier this should be worse that the voltage division effect? Again this should be worse for the bass response. We have also seen it with some of the amps measured here that when tested with real loads the THD for the bass frequency increases a lot.
 
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NDRQ

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Thanks.
Not sure but maybe the Chord Hugo 2 was, where the bass distortion went high, when used real test with headphones.
Amir said he will check other amps behaviour, but i dont know what happened after..
 

solderdude

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"When the headphone amp has an output resistance higher than 10 Ohm the HD650 will play louder than the K7** at the same volume knob setting due to voltage division. "

What is the exact math behind this?

The voltage across the headphone relates to the impedance of the headphone and the output R of the source.
U headphone = U unloaded x R headphone / (Rheadphone + R out)
As R headphone is lower in the K7** and Rout is a constant the voltage across the headphone will be relatively lower for 60 Ohm headphones than for 300 Ohm.

I checked your link and based on that, maybe not totally a myth the "hard to drive K712" , because they need much higher voltage than 95% of the listed headphones and in the same time they also need high current. Maybe this can be challenging workload to many amp.

You have to crank up the volume control a bit higher compared to most other headphones. It is about equally 'hard to drive' as the HD650 in that regard.
Yes, a phone can't drive the K7** and HD650 as loud as low impedance headphones. This does not make it hard to drive, it just needs a bit more voltage.
60 Ohm isn't a very low impedance and most amplifiers that can supply a bit more voltage won't have any trouble driving 60 Ohm.
Yes, some of the OTL all tube amps may not be able to drive it as well as a 300 Ohm. So for those amps the K7** is 'harder' to drive than any 300 Ohm headphone.
Both the voltage it needs nor the current that goes with it (current is not supplied it is drawn) are 'difficult' for amplifiers.

And another question: How is the output impedance effect the headphone frequency response?
Is there a way to estimate the effect of the output impedance to the headphone frequency response?
I mean this seems like a good way to alter frequency responses.

To estimate the influence you need to have the impedance plots and know the output resistance of the amp.
With this data and some math (and dB conversion) you can accurately calculate how the sound changes.
As this requires math and knowledge I find it easier to measure headphones at 0 Ohm and 120 Ohm and one can guesstimate for the in between values.
That's why I measure some of the headphones that have a varying impedance plot and show the effect in dB directly.
Not all headphones have a varying impedance.
The frequency response only changes (normal one driver dynamic headphones that aren't that well damped) around the resonance frequency. Most headphones don't sound better at a higher output R but some do. This is why my designs have selectable output resistances in 3 steps.
 
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