[Chairman]

Hi,
 
Just a question out of curiosity. I've heard a lot of people say that higher impedance headphones can't really be driven by unamplified sources, and that the volume would be very lacking etc. My DT770s and 880s (both 250 ohms) have no volume issues plugged into the front panel jack of my PC (Xonar DX card). I usually keep the volume at about 50% and it's plenty loud. I'm aware volume is largely subjective, but I've turned it up past 75% and I have a hard time believing anyone would consider that to be too quiet. I do own a headphone amp, but I'm just curious as to why this is...is there generally some kind of amplifier in the front panel jack of computer audio that I'm overlooking? Is it just an exaggeration that higher impedance headphones would be too quiet without an amp? Did I just get (un)lucky with both my headphones?
 
Thanks

 

[stv014]

Not all "unamplified" sources are quite the same. Also, there are large differences between what each person considers "loud enough" (even if some will not admit it); for an increase of 10 dB, which is perceived as about twice as loud, you need 10 times as much power. What you are listening to makes a significant difference as well: modern pop music with heavy dynamic compression might need up to 20 dB less peak level (that is, 100 times less peak power) to reach the same average loudness as a very quiet classical track. So, it is highly subjective what is loud enough, and you can only trust your own ears.
 
If your headphones sound fine (not noticeably different than when amplified at matched levels) and plenty loud enough without an amp, then there is nothing wrong with listening to them that way. Of course, loudness is not everything: the Xonar DX has an output impedance of 100 Ω, which affects the frequency response and distortion of the headphones (both mainly in the bass range: you get more bass resonance and distortion, but by an amount of less than 1 dB). You can decide if fixing those issues is worth it. However, the card does not clip even at maximum volume - as expected from a device that is intended to be used mainly as a line output.
 
By the way, I had similar experience with almost exactly the same setup (the only difference is that it was a Xonar D1 instead of DX, but these cards are basically the same other than the PCI vs. PCIe interface).

 

[NA Blur]

From what I remember the loudness level desired and headphone sensitivity set the output power need to reach said volume.  This has nothing to do with resistance.
 
From the power requirement we work backwards to find the voltage needed.  This is seen going from the Joule's law ( P = V^2/R for constant voltage sources like amps ).  From there we can start to see that as resistance goes up the power draw from the amp goes down.  Too high of resistance the too much power draw will be needed to reach a specific volume.
 
Working with Ohm's law and understanding the voltage needed from the Joule's law calculation we see from:
 
V = I*R that as the resistance goes up the current will go down to keep the voltage constant.  This is one reason high impedance cans can be a good thing so they do not draw too much current from a source.  This was a design implementation in years past to allow multiple high impedance headphones to be plugged into the same source without drawing too much current from that source.
 
In the end it depends upon whether the current is the limit or voltage.  Take a portable player.  It may be limited to just 5 volts peak to peak out.  This means that if for some reason more than 5 volts is required to get to a specific loudness then there is no way the source will provide it.  This is a crude example, but you get the idea.
 
You can read more here:
http://en.wikipedia.org/wiki/Headphones
 
and
 
http://www.apexhifi.com/specs.html
 
In short you go from the SPL using Sensitivity to find the power requirement, from there the current / voltage can be acquired.  If the amp can deliver both the current and voltage required to achieve the SPL desired using the impedance of the headphone then it really does not matter what the impedance is of the headphone.

 

[stv014]

By the way, an interesting thing about the Xonar D1/DX is that it can output about the same (relatively low) amount of power into 32 and 250 Ω because of its high output impedance.

 

[PurpleAngel]

  Hi,
 
Just a question out of curiosity. I've heard a lot of people say that higher impedance headphones can't really be driven by unamplified sources, and that the volume would be very lacking etc. My DT770s and 880s (both 250 ohms) have no volume issues plugged into the front panel jack of my PC (Xonar DX card). I usually keep the volume at about 50% and it's plenty loud. I'm aware volume is largely subjective, but I've turned it up past 75% and I have a hard time believing anyone would consider that to be too quiet. I do own a headphone amp, but I'm just curious as to why this is...is there generally some kind of amplifier in the front panel jack of computer audio that I'm overlooking? Is it just an exaggeration that higher impedance headphones would be too quiet without an amp? Did I just get (un)lucky with both my headphones?

When I use my DT770 Pro 250-ohm headphones with a Xonar DX, the volume max out was only a whisper.
Have you tried using your headphone amplifier connected to the Xonar DX and headphone to the headphone amplifier?
What is the make and model of the headphone amplifier?

 

[NA Blur]

  When I use my DT770 Pro 250-ohm headphones with a Xonar DX, the volume max out was only a whisper.
Have you tried using your headphone amplifier connected to the Xonar DX and headphone to the headphone amplifier?
What is the make and model of the headphone amplifier?

 
If this is the case chances are you have a volume set very low somewhere else.

 

[Chairman]

  When I use my DT770 Pro 250-ohm headphones with a Xonar DX, the volume max out was only a whisper.
Have you tried using your headphone amplifier connected to the Xonar DX and headphone to the headphone amplifier?
What is the make and model of the headphone amplifier?

 
The headphone amp is the FiiO E17. I actually haven't used it yet as it's currently in shipping, so I wouldn't be able to tell you much about my experience with it. I'm planning to use it with the Xonar via SPDIF, since my 5.1 speakers are occupying the line outs on the Xonar. I do also have a Focusrite Scarlett 8i6 interface which I use for recording, but the headphone amp in that sounds pretty terrible for music playback and has more of an issue driving the headphones than my front panel jack (but I'm fairly certain that's an issue with the Scarlett).
 
I've tried using a few different low impedance headphones with my front panel, like some Bose on-ear headphones, ATH-M50, Turtle Beach headset, etc, and I definitely have to turn the volume up higher for the Beyers to reach a comparable volume to the other headphones, but it's definitely not whisper volume on either my DT770s or DT880s. Like I said, even having the volume at 50% in the Xonar control panel software is plenty loud...subjectivity aside, I definitely don't think anyone would call it a whisper. I should mention that I haven't tried plugging them into the back panel of the Xonar. I'll try that tonight and provide an update. I also have a laptop with onboard audio, I'll try the Beyers with that too.