Quote:
Originally Posted by
hans030390 
I've had my HD555s for a couple months now, and I've noticed that on some sources they sound pretty good! On some, they sound thin and lifeless. In my case, they sounded awful out of my iPod Touch 3G. Thin sound, no bass, etc. So, I hooked them up to my Xonar DX. I plugged them into the main output jack. They sounded great out of that! They're not bass heavy by any means, but they instantly sounded more full, involving...better in every way! Very enjoyable.
Wanting to use them as portable headphones, I decided to try out the Nationite S:Flo2. I figured the iPod Touch just didn't have enough juice for these, and I knew the S:Flo2 would be good. It's running the latest firmware (2.3).
However, my HD555s sound just as bad from the headphone out on the S:Flo2 as the iPod Touch! Thin, lifeless, no bass...same story. Disappointed and confused, I hooked them into the line-out of the S:Flo2. Now they sound great, just like from my Xonar DX! I've noticed some subtle differences hooking up my ATH-M50s to the HO and LO of the S:Flo2, but nothing compared to what happens to my HD555s.
Can someone explain to me what exactly is going on here?
Most likely it's the output impedance of those devices.
Imagine the output impedance like a resistor in series with the headphones - effectively a voltage divider. If the headphones had a fixed impedance throughout the audible frequency range, the voltage divider would just attenuate the signal by some dB.
But that's how the impedance curve looks like actually: HD555
Now imagine the output impedance was like 200 ohms. Around 80 Hz (bass) the voltage would drop about equally across the output impedance and the headphones (equals -6 dB).
However, at 1000 Hz most of the voltage would drop across the output impedance, effectively attenuating those frequencies much more than bass frequencies (where the impedance peak can be found).
So it has nothing to do with "enough juice" or not. In fact, you can easily build an impedance adapter which is just two resistors in series with the left and right speaker and see for yourself how big the influence on the frequency response is, especially with the HD555 because of their big impedance peak.
This way you can easily increase the output impedance until you reach the point where you think the HD555 sound great.
Portable players usually have a low output impedance. From what I've seen, around 20 ohms max.
With stereo receivers it's not unusual to see 120 ohms or more.
The xonar dx seems to be somewhere in between.
Edited by xnor - 12/10/10 at 4:36am
If you've ever made a cable yourself making an impedance adapter should be a breeze.
