[mrcrazyshoes]

Sorry if this is a stupid question but I'm new to all of this hi-fi stuff. I have a Sony receiver (STR-DH510) and it says that it outputs 8 ohms. I also have Sennhieser 558's and they are 50 ohms. When I plug my headphones into the receiver using the headphone out, the bass is extremely increase and its very annoying. Why is this happening and how can I fix it (other than using the eq)?

 

[mikeaj]

It's probably saying that the speaker output is intended for 8 ohms speakers, not the the output impedance is that much.
 
From the symptoms it sounds like the headphone output is just the speaker output with a huge-valued resistor in between, because they don't really care about how the headphone output sounds.  This is a huge problem if your headphones have highly variable resistance.
 

At a given frequency you have the below because the source output impedance (Z_s) is forming a voltage divider with the load headphone impedance (Z_L), where V_L is the voltage the load gets and V_s is the voltage from the source:

 
The source output impedance is generally just the same for different frequencies, while the load impedance may change significantly.  For lower Z_s relative to Z_L, you expect the ratio to be relatively constant no matter what Z_L is.  For difference in volume, take 20 * log10 of the ratio of V_L at one frequency compared to V_L at another frequency, assuming V_s is the same for both.
 

See here for some calculations:
http://docs.google.com/spreadsheet/ccc?key=0AjhinPmoO8atdE5PRkpkM2hhOGpoNnVqYVAzT083Y2c
 

Note the boost will be where the impedance is high in the above graph--around 90 Hz, in the bass.
 
Maybe you can use something like a FiiO E5 or E6 in between the receiver and the headphones, to avoid that problem.

 

[mrcrazyshoes]

Thanks for helping me understand this a bit more. So would you suggest having output from my sound card (which already has a headphone amplifyer) go to the receiver, then through the FiiO E5, and then to my headphones? 
I also have another question, with my sound card (Xonar DG) there are 2 settings, headphone and 2 speaker. The headphone setting omits a tiny, but annoying white noise sound while the 2 speaker setting doesnt. I would use the 2 speaker setting all of the time but it also seems to boost the bass slightly, while increasing the volume, is this also because of the ohm difference? Will there be any sound quality different between the two settings? Thanks a lot for replying!

 

[mikeaj]

No, just run the headphones from the sound card.  Skip the receiver for that.
 
I have no idea what it's doing between headphone and speakers mode, but I doubt there's actually a change in hardware configuration going on.  Check all the software configuration options again, like Dolby Headphone maybe being on, any DSP effects, EQ, etc.  The Asus cards also have a headphone impedance setting, though that doesn't do anything other than limit the volume in software if you select a lower setting.

 

[mrcrazyshoes]

Ok thanks for all of your help! Im just going to leave it on the 2 speaker setting.

 

[PurpleAngel]

Quote:

Thanks for helping me understand this a bit more. So would you suggest having output from my sound card (which already has a headphone amplifyer) go to the receiver, then through the FiiO E5, and then to my headphones? 
I also have another question, with my sound card (Xonar DG) there are 2 settings, headphone and 2 speaker. The headphone setting omits a tiny, but annoying white noise sound while the 2 speaker setting doesnt. I would use the 2 speaker setting all of the time but it also seems to boost the bass slightly, while increasing the volume, is this also because of the ohm difference? Will there be any sound quality different between the two settings? Thanks a lot for replying!

What gain (Ohm) setting is your Asus Xonar DG set at?
What make and model headphones are you using?