Again, that's not what I said, but I have the feeling your objectives differ. Fletcher Munson notwithstanding, listening to underpowered insensitive Headphones -works- at lower levels, but you don't really get them to perform how they should. To get them to perform to specs, they need enough power, not only to get them louder.
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Best portable USB bus powered headphone amp
- Thread starter lsanbourne
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solderdude
Grand Contributor
That is because at low level all amplifiers provide can easily provide voltage AND current at 'normal and low' listening levels.
The output voltage will be exactly the same and as planars are resistive the current is also exactly the same.
That is ... right up to the point where either the voltage or current limits are reached. Then the more powerful amp is always in the advantage.
LCD2 exists in various forms and ranges from 50 to 70 ohm and sensitivity can be between 104dB/V and 109dB/V.
Sundara = is 104 to 105dB/V and between 37 and 43 ohm.
When your LCD2 plays noticeable louder than Sundara it is likely near 109dBV.
Should you measure the output of an amp under actual load you will not see any difference... there can't be because no limits are reached. The impedance is flat (resistive) and feedback in an amp ensures no load dependency.
So whatever you are hearing at low level is due to frequency response differences between the models or max. output voltage dependent.
Most USB audio interfaces can not provide much 'power' and have issues with providing current.
In the latter case (current limiting and higher output R) the Sundara has the disadvantage and the output will clip earlier as the impedance is lower (current limiting) and lower output voltage dues to voltage division with a lower headphone impedance.
Chances are Sundara makes a lower power output clip much earlier than LCD2 (higher impedance, higher sensitivity).
nonsense.
An amplifier provides an output voltage.
The current draw is determined by the headphone resistance.
As long as neither output voltage limit nor current limit is reached the amps all will perform exactly the same.
The specs of the headphones don't change under different output voltages (at least not with these planars).
Perception can.
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Probably that's what I was hearing then. As for them not sounding differently underpowered, this would be theoretically correct. I would however be willing to bet (if I were a betting man) that their impedance isn't perfectly linear when under minimum voltage requirements.
solderdude
Grand Contributor
I am 100% certain the impedance of planars will remain perfectly linear (not so with most dynamics at higher SPL) so if I were you I would not place a bet on that one.
The impedance of both of these planars is resistive in the audible range regardless of the applied voltage.
When the voice coils start to glow red and the membrane melts (many Watts continuous) the impedance might vary ...
"When this happens and you turn up the volume beyond that point (depending on how 'hard' the clipping is) the loudness (volume) of the sound will still increase and bass levels will 'suffer' first as they have the largest voltage swing. The sound will turn 'nastier' but the volume of the sound keeps increasing but NOT the bass. That is clipped so stays 'behind'.I am 100% certain the impedance of planars will remain perfectly linear (not so with most dynamics at higher SPL) so if I were you I would not place a bet on that one.
The impedance of both of these planars is resistive in the audible range regardless of the applied voltage.
When the voice coils start to glow red and the membrane melts (many Watts continuous) the impedance might vary ...
In these cases using an amplifier that has a higher voltage and or current limit moves the voltage clipping point upwards and so the clipping occurs at higher listening levels.
At some point, where peak SPL of 120dB is reached, the sound is so loud you won't go there simply because it is unpleasant for longer periods.
You can listen to 120dB SPL peaks for about a minute and this is impressively loud and because of equal loudness contours has tremendous bass power (makes Amirs earlobes shake). But you won't be doing that for long.
This means that when the amp chosen for driving your headphone can deliver the needed voltage (= drawn power, not delivered power) without clipping and the amplifier has enough gain and the music source has enough output voltage then having more available power is pointless.
Yes, having 3dB more headroom is desirable but not needed for normal listening levels.
When amplifiers (even a dongle has an amplifier inside) clips at SPL levels of say 90dB SPL in a specific headphone then it will sound as if it struggles with the bass. And it does. It clips the bass as that has the highest amplitude.
90dB SPL for bass is NOT loud at all. 90dB of bass is about 30dB above the hearing threshold.
60dB SPL of bass makes the fundamental of that bass inaudible already while the rest of the music is at a enjoyable soft background level.
90dBA is loud and for bass fundamentals to reach that level the actual SPL = 120dB !!
So in short... when you want to use your headphone at all kinds of levels it needs to reach voltage levels that can make it produce 120 to 123dB SPL. You don't need as much if you never play loud. Around 110dB is good for comfortable loud and 100dB ensures normal listening levels never clip.
That said.. efficiency levels are often given at 1kHz or 500Hz. Looking at the frequency response of headphones you will find most of them roll-off and some 'boost' in the lows. This too has an effect of how bass is perceived. When you have to boost it the voltage limit is reached much, much, much earlier as well.
It is a complicated 'play' between headphones, voltage efficiency and voltage levels that can be reached which determine how impressive bass will be.
It is not costly to make amps that can provide enough to power all but very rare and inefficient headphones.
There you have it. It's all science not magic and the laws of that science cannot be broken.
Audio may seem like magic and things may seem 'inexplicable' but they aren't.
Aside from all these technical things that need to be right, including distortion and frequency response and in lesser sense phase, there are other aspect that also have great impact."
Do you remember writing this? Multiple users report the same thing, "bass goes limp" on the Sundara. I guess the output of the Babyface is so low that that happens at "quiet" levels, your description of the volume getting louder, but bass staying behind also seems accurate to my experience. If instead, you simply switch amps at the same volume, bam, there's all the bass and all the "life" in the sound (other users reported them feeling "lifeless" with weak amps).
Also, I just realized there's one point not being considered in the case of the OP and me with regards to the Babyface Pro FS and its puny amp xDI am 100% certain the impedance of planars will remain perfectly linear (not so with most dynamics at higher SPL) so if I were you I would not place a bet on that one.
The impedance of both of these planars is resistive in the audible range regardless of the applied voltage.
When the voice coils start to glow red and the membrane melts (many Watts continuous) the impedance might vary ...
We're talking about playing music that is being captured and before any form of rendering. Those are QUIET sources. Probably around -23 to -18 LUFS averaged, against -12 to -9 LUFS finished masters for an average listener.
The amp has to make up for all that level, and there is where I suspect you're going to experience a lot of non-linear behavior without a serious amount of headroom at hand. Even if all things considered, impedance remains the same, the behavior cannot be called linear (considering what I and others have experienced, and what you wrote in that post from 2021). Non-linear in which way though, how would you describe it?
solderdude
Grand Contributor
The goal of an amp is to provide an output voltage in a resistance.
It does not care about LUFS, dynamic range, or whatnot.
The amp (soft) clips or it doesn't.
The clipping can be caused by either a voltage limit or a current limit being reached.
This is the point where all headroom is exhausted (the 'knee' in the distortion plots)
In the case below the knee (crosshairs) is caused by the current limiter.
This current limit forces the output voltage to clip at 1.6V where the max output voltage of the amp section (in Amirs measurements) did not even reach the voltage clipping point (which is somewhere just above 2.6V)
This is a big issue in many of the external USB sound cards around.
This simply is a matter of the amp section being too wimpy and thus an output power question (headroom) and not a power 'quality' issue.
2 amps of very different power ratings when driven below the saturation point of the weakest amp will sound exactly the same.
Any perceived differences are either caused by the weakest amp clipping or imaginary or by a substantial difference in tonal balance between the headphones.
Non linearity of a driver only occurs at higher SPL (distortion) not at low levels.
This can be seen as compression above a certain SPL (very soft 'clipping')
The lower the level the more linear the behavior of the driver is.
Only at very low levels (below audible levels) an extremely small current variation might not result in displacement of the driver.
We are talking of levels below the noise floor.
Portable USB devices with a headphone out will always be limited.
One can increase those limits easily when using USB-C as that is allowed to draw more current than 'normal' USB.
A way to do that (internally) is to use a battery inside which in turn drives DC/DC converters.
It does not care about LUFS, dynamic range, or whatnot.
The amp (soft) clips or it doesn't.
The clipping can be caused by either a voltage limit or a current limit being reached.
This is the point where all headroom is exhausted (the 'knee' in the distortion plots)
In the case below the knee (crosshairs) is caused by the current limiter.
This current limit forces the output voltage to clip at 1.6V where the max output voltage of the amp section (in Amirs measurements) did not even reach the voltage clipping point (which is somewhere just above 2.6V)
This is a big issue in many of the external USB sound cards around.
This simply is a matter of the amp section being too wimpy and thus an output power question (headroom) and not a power 'quality' issue.
2 amps of very different power ratings when driven below the saturation point of the weakest amp will sound exactly the same.
Any perceived differences are either caused by the weakest amp clipping or imaginary or by a substantial difference in tonal balance between the headphones.
Non linearity of a driver only occurs at higher SPL (distortion) not at low levels.
This can be seen as compression above a certain SPL (very soft 'clipping')
The lower the level the more linear the behavior of the driver is.
Only at very low levels (below audible levels) an extremely small current variation might not result in displacement of the driver.
We are talking of levels below the noise floor.
Portable USB devices with a headphone out will always be limited.
One can increase those limits easily when using USB-C as that is allowed to draw more current than 'normal' USB.
A way to do that (internally) is to use a battery inside which in turn drives DC/DC converters.
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There is an Amir review for the RME Babyface Pro FS here, the 6.35mm hp out has an 11Ohm impedance. That would be the high power out (amir measured that at 56mW, it's rated 90mW, but in this case its specs make them bad for low-impedance headphones). The low-power out, the 3.5mm connector, has a 0.1 Ohm impedance. So I was just using the wrong out for the Sundara when I used the headphone out in that unit (thank goodness that is maybe 5 years behind me). But that is not all. RME chimed in in that thread:
--- "Thanks for this review, Amir!
This unit is USB bus powered. As such we had to make sure it will not cease operation the moment you record the take of your life. The whole unit is carefully balanced between power consumption and performance. The reason for the two headphone outputs is part of that - a high power headphone output can easily shut down USB bus power with higher levels on low impedance phones. So we added two outputs with separated driver stages. One gives a high output level, but its output impedance (a 10 Ohm resistor) limits the available current. Note that changing this to 0 Ohm would not have resulted in higher output power as measured on a 300 Ohm load! Only higher levels could do that, and these are not possible without upping the power consumption. Also the effects on frequency response and damping are no problem with phones of 80 Ohms and up.
For low impedance headphones 10 Ohms is too high, so we added a second output (3.5 mm) that is limited to a 6 dB lower output level, but near zero Ohms output impedance. From my practical experience with a lot of different headphones, you will not have a problem with either low or high impedance ones, and you could even connect two at the same time (thanks to the separated driver stages)." ---
The quieter output is too quiet for quiet sources on harder to drive headphones. A capped out low-output amp cares about LUFS, you can't turn the dial past zero, and you can't add gain to the digital level on the interface without causing digital clipping at some point depending on dynamics (whether the theory says otherwise or not, you only need to get some raw signals and try to work with them to experience that). You could limit your mixbus, but you don't want to do that at a very early stage, and certainly not if you're working on classical music.
So brother, it wasn't just my perception that was causing the differences. You either have the -6db neutered out with the correct impedance on that device, or you have the one that's skewing frequency response on the Sundara that would've had more power to work on quiet sources (albeit still super weak). Going from those two outs, to the UCX-2 (0.1 Ohm out, 240mW), or to an ADI-2 FS (0.1 Ohm 700mW), or even to the Fosi SK02 (280mW or 1.100mW balanced) connected to the BabyFace via optical SPDIF (which is my mobile setup now) makes a ton of difference on how the Sundara sounds. BTW OP, Fosi SK02 is very portable and an absolute upgrade connected to the Babyface Pro FS, I don't need any other devices and only need an extra USB-C charger around to power that, plus I can keep using the top notch RME drivers to get sound out, can EQ my headphones in TotalMix before sending that to its ADAT out, and can adjust digital levels before conversion. And I still have all the things the Babyface Pro FS does great with me when I'm out working.
I stand by what I said, the hp out on the Babyface Pro FS is its glaring weak spot. I could hear that. Now I can see the data xD
I was wrong in assuming the cause was just lack of power. But for working on unfinished sources with less sensitive headphones, that's also a problem that (otherwise great) interface manages to present.
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solderdude
Grand Contributor
Lack of power is actually the reason.
You were clipping the output.
10ohm output resistance is NOT an issue with planars other than the super low impedance ones.
Sundara would be down 2dB on the 'high Z out' and the LCD 2 merely 1.3dB down.
Yes, that kind of output power is a bit low for planar magnetics.
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Either way, it was unreliable and caused me to have to work harder and listen to more sources to get a good picture if what was going on. The moment I finished my room and got it working full range and dampened enough, it stopped serving as added perspective.
Btw I was also using spatialization and corrective software with it that needed an extra 6.5db of headroom. That boosted the lows more than anything, so if you take that into account with the quiet sources and the subpar damping on the drivers that your waterfall graphs demonstrate (maybe aggravated through the impedance mismatch), I guess that was the last straw. The LCD 2 kind of always sounded like itself btw, even though I almost never use it with the Babyface (I don't like carrying them around...), so I can't tell that for sure, other than it was way more dramatic of a step up (or down) with the Sundara.
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