active monitor connecting cables

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vjekob
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active monitor connecting cables

Post by vjekob » Thu Jan 12, 2017 6:12 pm

I have active monitors and would like to be able to connect either
an audio interface or pc audio card/smartrphone to them directly.
For connection of the audio interface I'm set:
I have two "speaker cables" with XLR(speaker side) -> /1/4" male(audio interface side ) connectors / balanced cables.

If I want to reuse those "speaker cables" instead to connect the pc audio card output / smartphone
to the speakers, I would like to buy a spliter cable which will just plug into those cables
i.e. 1/8" male connector (pc audio card side) -> 2 * 1/4" female (connect to the two "speaker cables").
Does the 1/8" connector have to be stereo (2 black stripes on the plug) or I've also seen splitter cables
as advertised for spliting smartphone -> earphones+mic which have 3 black stripes on the 1/8" male connector ?

If I want to connect pc audio output/smartphone output directly to an audio interface,
this requires 1/8" male stereo (smartphone/pc side) -> 1/4" male stereo (audio interface side) - correct ?

ColinPark
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Re: active monitor connecting cables

Post by ColinPark » Fri Jan 13, 2017 7:13 am

With 1/4" or 1/8" male plugs, we need to distinguish between TS and TRS.
  • T = tip (carries one channel of audio)
  • R = Ring (if present, carries another channel of audio)
  • S = Sleeve. (carries the ground).
Now, an XLR (x = model number, the James Cannon X-series) (L = locking)(R = rubber between the pins) also carries 2 audio channels and a ground, so they do the same thing in principal. However, the typical usage of TRS is to have an unbalanced stereo signal with the tip carrying the left channel and the ring carrying the right channel. XLR typically uses both channels for the same signal, but one version is phase reversed. So it's a balanced mono signal when all's said and done. Phantom power is often transmitted by putting the audio signals 48V DC above the ground.

TRRS has a second ring. The shaft has 3 insulating bands, and thus 4 contact points. The second ring typically carries the mic for a cell phone, but it could be used for other things.

Now your audio card is almost certainly putting out a stereo unbalanced signal. When you convert this to 2x 1/4" female, you want one of them to be left channel, the other to be right. In other words, map the 1/8" male tip to female #1's 1/4" tip, AND map the 1/8" male ring to female #2's 1/4" tip. You do not want a stereo Y-cable. It produces 2 identical female 1/4" TSRs, and when you plug a TS male into a TRS female, you ignore the ring. You get just the left channel, and this Y-cable will give you 2 left channels and 0 right channels.

That assumes your XLR to 1/4" has a TS on the 1/4" side. If you have a TRS on the 1/4" side, then you've got a more interesting situation. The speaker expects a balanced signal (mono on one pin, inverted duplicate on the other).

I don't remember what you're supposed to do to get past this (so double-check what I'm saying).

Plugging a TRS male into a TS female should cause the second signal to be missing. (No ring contact.) This could be a source of noise. It would be better if it were grounded, and I seem to remember that's what happens when you build an adapter for this situation. In any case, there's no phantom power to worry about, so you'd just get the one (tip) version of the signal to the speakers, and it should "work". Mostly. Unless there's an impedance mismatch issue. That's another topic, however.

As for connecting sound card to audio interface, you have to determine if the audio interface expects balanced line inputs. Balanced TRS inputs are quite common on audio interfaces. Like the speaker example, this means a mono signal and it's inverse, not a stereo signal. The same issues about the ring signal being open apply. But if your interface expects or accepts a stereo unbalanced line level signal, then a simple patch cable 1/8" to 1/4" TRS male-male would do fine.
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vjekob
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Re: active monitor connecting cables

Post by vjekob » Fri Jan 13, 2017 8:39 am

Thanks, much appreciated !
Once I go through what you've written in detail, I'm sure everything will be clear.

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