HELP - strange input jacks on new speakers...

[itsme9003]

Hey guys, just picked up a very old set of computer speakers, the Harman Kardon HK595. Has two satellites plugging into a powered sub.
 
What I'm confused about are the input jacks on the rear of the sub (see pic). There is a lime-colored "stereo" jack, a black "rear" jack, and a yellow "digital" jack, all input - I've never seen a 3.5mm digital input jack... Also, why would this have a "rear" input jack if it only has two satellites?
 

 
The included cable connects all three of these jacks and ends in three separate 3.5mm connectors (see pic) - how do I plug these into the back of my onboard 8-channel soundcard? Do I plug in just the lime connector, or should I plug in the other two as well? Any help appreciated, thanks.
 

 

[ProtegeManiac]

  I've never seen a 3.5mm digital input jack... 

 
Old PC laptops had a combo analog earphone output+toslink digital on the 3.5mm jack. MBPs still have this I think.


 
 
Nowadays we have 3.5mm coaxial digital jacks on some DAPs:
 


 
 

  Also, why would this have a "rear" input jack if it only has two satellites?

 
Must be some kind of phantom satellite surround simulation, the same way that gaming headphones come with a USB soundcard that simulates 6ch audio on stereo headphones with only two dynamic drivers, except here it will be processed by the sound card and those speakers tweak the soundfield effect on just those two channels to "throw" them behind you (more like farther out to the side, perhaps). Some better motherboards have the same feature on their on-board sound. Dolby Headphone, EAX, and Razer Surround are the most popular software programmes for these.
 

 
...how do I plug these into the back of my onboard 8-channel soundcard? Do I plug in just the lime connector, or should I plug in the other two as well? Any help appreciated, thanks.

 
Don't plug in all of them, your auto-sensing jacks on the motherboard will interpret that as a 6ch output to a multimedia speaker  and you can lose the center channel signal (I'm not aware of any current speakers that have only four channels and thus do a phantom center, same way it's done on stereo speakers). You can probably just use a headphone cable extension on the lime jack, problem is the other jacks (most likely the one for the rear satellites) might pick up noise if not plugged in. Won't hurt to try if you can get the cable cheap.
 

 

[itsme9003]

   
Old PC laptops had a combo analog earphone output+toslink digital on the 3.5mm jack. MBPs still have this I think.
 
Nowadays we have 3.5mm coaxial digital jacks on some DAPs:
 
Must be some kind of phantom satellite surround simulation, the same way that gaming headphones come with a USB soundcard that simulates 6ch audio on stereo headphones with only two dynamic drivers, except here it will be processed by the sound card and those speakers tweak the soundfield effect on just those two channels to "throw" them behind you (more like farther out to the side, perhaps). Some better motherboards have the same feature on their on-board sound. Dolby Headphone, EAX, and Razer Surround are the most popular software programmes for these.
 
 
Don't plug in all of them, your auto-sensing jacks on the motherboard will interpret that as a 6ch output to a multimedia speaker  and you can lose the center channel signal (I'm not aware of any current speakers that have only four channels and thus do a phantom center, same way it's done on stereo speakers). You can probably just use a headphone cable extension on the lime jack, problem is the other jacks (most likely the one for the rear satellites) might pick up noise if not plugged in. Won't hurt to try if you can get the cable cheap.
 
 

 
Hmm...still confused about that yellow plug. Are you saying back in the day that the yellow would have connected to a toslink digital output from a 3.5 mm jack? If that's the case, why would the proprietary cable combine all three inputs into one cable? I feel like that design meant for all three 3.5mm plugs to be used/plugged in simultaneously, but that makes no sense...
 
I'm also confused about that headphone extension - what are you suggesting I do with it? If the black "rear" plug really is a surround simulation, I feel that I should at least plug in the lime and black into my onboard 8-channel sound card, leaving the yellow unplugged. Is this correct?

 

[Honkytime]

   
Hmm...still confused about that yellow plug. Are you saying back in the day that the yellow would have connected to a toslink digital output from a 3.5 mm jack? If that's the case, why would the proprietary cable combine all three inputs into one cable? I feel like that design meant for all three 3.5mm plugs to be used/plugged in simultaneously, but that makes no sense...
 
I'm also confused about that headphone extension - what are you suggesting I do with it? If the black "rear" plug really is a surround simulation, I feel that I should at least plug in the lime and black into my onboard 8-channel sound card, leaving the yellow unplugged. Is this correct?

I think if you just plug in the green everything will work just fine. the other inputs just give you more options for inputs

 

[itsme9003]

  I think if you just plug in the green everything will work just fine. the other inputs just give you more options for inputs

ok, that's what i originally thought. what about the rear plug though? I assume that has to do something right?

 

[Honkytime]

 
ok, that's what i originally thought. what about the rear plug though? I assume that has to do something right?

music and sound output from your computer is produced in stereo so unless the music or sound is made to output 4 channels it most likely do nothing.

 

[ProtegeManiac]

   
Hmm...still confused about that yellow plug. Are you saying back in the day that the yellow would have connected to a toslink digital output from a 3.5 mm jack? If that's the case, why would the proprietary cable combine all three inputs into one cable? I feel like that design meant for all three 3.5mm plugs to be used/plugged in simultaneously, but that makes no sense...

 
I'm just as stumped with that one, but I no longer have an old enough PC here for me to check the soundcard outputs.These could be from way back when 4.0HT with Dolby Phantom Center was a thing, hence no center channel on it (and soundcards back in the day might have had only these three, with only digital and no consideration for a center channel on the third plug).
 

 
I'm also confused about that headphone extension - what are you suggesting I do with it? If the black "rear" plug really is a surround simulation, I feel that I should at least plug in the lime and black into my onboard 8-channel sound card, leaving the yellow unplugged. Is this correct?

 
You could, but you will have to make sure to override the auto-detect sockets, especially if you're playing games. While that won't affect 2.0 channel music as the lime connector carries FL and FR signals (unless sending an analog signal through a digital input causes any noise), I don't know how that will affect games. You have to set it to do only stereo, and there won't be any sound going through the phantom surround; otherwise, selecting 5.1 will leave you with a non-existent center channel unless that game or soundcard can do phantom center. Considering it really can't throw the sound behind you, just manually set it to stereo output.

 

[itsme9003]

Ok, that makes sense.
Thanks everyone for your input. These speakers actually sound pretty decent for how old they are and for how much I paid (free )