[Aelius]

My sound card (Creative Sound Blaster Z) has a headphones jack and an optical-out port. I use the optical-out port to go to my external DAC/amp, to which I plug in my HD600 headphones.

But sometimes I want to watch movies and TV on my computer with someone else simultaneously. So I tried plugging in some other headphones into the sound card's headphone jack. This way, I'll have two headphones connected at once. To my surprise, the computer's audio does indeed come out of both headphones.

How does this work? Is there any downside to this? For example, my HD600 headphones are high-impedance, unlike the cheapo ones I plugged into the headphones jack. How is it outputting an apparently clean signal to both headphones despite vastly different impedance?

I mean, I'm glad this seems to work, I just... feel like it's too good to be true.

 

[MindsMirror]

The Soundblaster Z is able to send the same digital signal to both the internal DAC and the optical transmitter. From that point on, the signal paths are totally independent. The amp/DAC which you connect to the optical output doesn't know anything about what's connected to the headphone jack, and vice versa. In fact, you could shove the other end of the optical cable into a potato, the headphone jack wouldn't care. The optical transmitter wouldn't even care, it's essentially just flashing a light into a tube and hoping that someone on the other end of the tube is watching.

 

[Aelius]

The Soundblaster Z is able to send the same digital signal to both the internal DAC and the optical transmitter. From that point on, the signal paths are totally independent. The amp/DAC which you connect to the optical output doesn't know anything about what's connected to the headphone jack, and vice versa. In fact, you could shove the other end of the optical cable into a potato, the headphone jack wouldn't care. The optical transmitter wouldn't even care, it's essentially just flashing a light into a tube and hoping that someone on the other end of the tube is watching.

Oh hey, thanks! I remember your name from various other threads here on head-fi years ago that I was looking through while trying to research this question. Thrilled to see you're still around!

Out of curiosity, why doesn't this work when I try plugging the 3.5mm headphone jack into any other headphone port? I tried plugging into the headphone jacks on all of the following devices, and none worked:

Monitor
Case front panel
Microphone
Speakers (and these speakers are also plugged into the SBZ!)

Thanks again!

 

[MindsMirror]

If you plug into most of the other ports, windows will switch the payback device from your SBZ to that other device. It works with the SBZ because it has the "send stereo mix to S/PDIF" option, so when it is the payback device for the headphones, it can also output to the optical. If you connect to those other ports, the SBZ isn't receiving the audio data at all, so it can't send anything to the optical port.

You might be able to get the front panel port to work if you connect the header from your case directly to the SBZ instead of to the motherboard.

Not sure about the speakers, maybe you just don't have that setting enabled when it's set to speakers.