Splitting audio signal degrades quality.. sometimes?, Can't find a clear answer to this Options

[midkay]

Hi all, there is something I have been trying to figure out for a while.

I own a Grado SR-80i and a Triple-Fi 10. The SR-80i sounds great through my PC's Xonar D2X card, and very good through my iPhone 4. The Triple-Fi I find to sound overly flat on my D2X, but very good on my iPhone. In any case, when I split the audio from my D2X to both sets of phones, there is a very noticeable drop in sound quality, a strong flattening of the soundstage. This effect is nearly unnoticeable when I split my iPhone's signal in the same way. I suspect the TripleFis may be a key factor, since they make my D2X sound extremely flat all on their own. Can anyone tell me what's happening here?

[Kohlrabi]

Please define "split".

Every combination of headphones and DACs can lead to a different sound. First, the impedance matching of your headphones to the DAC may be non-optimal. Too high output impedance compared to the headphone impedance can lead to non-linearities in the frequency response, essentially distorting the audio. nwavguy suggests following the 1/8-rule, meaning that your headphones should optimally have 8 times the impedance of the DAC to avoid such problems.

Another difference can be the sensitivity of the headphones, which controls the power delivered to your headphones. Higher sensitivity can lead to louder audio and hence to perceived higher quality.

Also the frequency response of the involved devices might be vastly different. Maybe you prefer some of the combinations and not the others? Optimally (IMHO) the FR should be flat so that you can easily apply equalizing to alter the sound to your liking.

EDIT: Gah, I should read more carefully

This post has been edited by Kohlrabi: May 16 2012, 08:21

[nevermind]

The answer is to do with the output impedance of each amplifier. In normal headphones there is a impedance change in the bass, at the drivers resonance frequency. It is well known the output impedance of an amplifier can change the amount of bass in phones, at their resonance frequency, however, the triple fi phones use a crossover, and as such they have more then one bump in their impedance. It is very likely the crossover is in the mids, and that is where the change in sound will manifest. (as well as in the lows)

Splitting the signal to 2 headphones will show the amp both impedances in parallel, so it will see a 16 Ohms load (assuming they are 32 each). This probably overloads the amplifier, and adds more changes in frequency response due to both nonlinear impedances in parallel.

This post has been edited by nevermind: May 16 2012, 09:44

[Arnold B. Kruege...]

Hi all, there is something I have been trying to figure out for a while.

I own a Grado SR-80i and a Triple-Fi 10. The SR-80i sounds great through my PC's Xonar D2X card, and very good through my iPhone 4. The Triple-Fi I find to sound overly flat on my D2X, but very good on my iPhone. In any case, when I split the audio from my D2X to both sets of phones, there is a very noticeable drop in sound quality, a strong flattening of the soundstage. This effect is nearly unnoticeable when I split my iPhone's signal in the same way. I suspect the TripleFis may be a key factor, since they make my D2X sound extremely flat all on their own. Can anyone tell me what's happening here?

I checked the specs for the Xonar D2x, and find that none of its output jacks are specified for use with headphones. Various sources put its output impedance at 10 to 100 ohms. I expect that the second number is more likely for line level outputs.

Hooking most headphones to a jack with 100 ohm source impedance will be very likely to change its frequency response in audible ways. Adding another pair of headphones will make things worse and interactions between the headphones is to be expected.

The Xonar D2X would be greatly improved as a source for headphone listening by adding a low cost headphone amplifier such as the FIIO E5.