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Handling audio output from two Skyview displays

N546RV

Well Known Member
OK, I've spent way too much time agonizing over how to handle this, which is usually a pretty solid sign that I'm overthinking something. I've got two 10" HDX displays and a Dynon intercom. Each HDX display has a left/right/ground pin for audio. The installation manual specifies that both displays should be connected to the audio input of the intercom:

If there is more than one display on a SkyView network, you MUST connect all displays’ audio outputs to the same audio panel input to ensure that audio is always heard. Electrically short the respective left and right outputs together for stereo mode (i.e., left-to-left and right-to- right) or connect all audio outputs together for mono mode. The same rule applies for audio grounds.

But I'm being really bothered by how to physically do this. Best practice would seem to be to use shielded cable for these audio runs, but then my wiring split ends up being somewhat complicated and bulky; in addition to the three window splices (which I'd need no matter how I do this), now I've got two shield terminations to handle instead of one.

The harnesses that came with the displays don't use shielded cable at all; they just have the three bare wires twisted together. I'm building up my own harnesses for most connectors, but I suppose I could grab those twisted pigtails and splice them together for my connection.

Possibly relevant here is the length of the runs. The intercom is right beside both displays, so the total harness length covered by this audio connection is about 18". Does the length of the run play a role in susceptibility to noise?

So that's where I'm at. Do I:

  • Run two shielded cables and splice them together?
  • Run the twisted bundles from the OEM harnesses and splice them together?
  • Just run three new wires, untwisted?
  • Do something totally different?

Seriously, this feels like one of those "do this simple thing and build on" moments. Please, shower your collective wisdom upon me. Surely there are lots of dual Skyview aircraft out there that have had to handle this.
 
The short answer is option #2:
- Run the twisted bundles from the OEM harnesses and splice them together?

I did this on four dual screen SkyView installs, works just fine.

Carl
 
Thanks, Carl. I think I just needed someone to reassure me that choosing the simpler option wouldn't cause the sun to go supernova or anything.
 
Don't know the what kind of output the Dynon uses but this sounds like bad advice to me, typically tying audio outputs together is a no-no.
I'm pretty sure if you lose the PFD for some reason lost audio from it would be pretty low on the priority list.
On a Garmin system only the audio from the PFD gets routed to the audio panel.
 
What Carl said. Dual screens will have a primary and backup assigned. If the primary goes offline, the backup becomes primary.

From the Intercom manual:
The audio outputs from all SkyView displays must be connected together before
connection to their respective pins of the SV-INTERCOM-2S. More detail is available in the SkyView System Installation Guide.
 
Dynon is aware that doing this may cause issues:

"SkyView systems with more than one display normally only output audio alerts from one display to minimize audio distortion. In a SkyView system that has more than one display and dual SV-EMS-220s/221s to monitor dual engines, EMS audio alerts are enabled from two displays. At moments when two displays are outputting EMS audio alerts, there may be minor “doubling” of audio alerts heard in the audio system."

So if you disable audio alerts from the second display then why even hook it up?
 
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Dynon is aware that doing this may cause issues:

"SkyView systems with more than one display normally only output audio alerts from one display to minimize audio distortion. In a SkyView system that has more than one display and dual SV-EMS-220s/221s to monitor dual engines, EMS audio alerts are enabled from two displays. At moments when two displays are outputting EMS audio alerts, there may be minor “doubling” of audio alerts heard in the audio system."

So if you disable audio alerts from the second display then why even hook it up?

Not my experience, and I do not disable audio alerts from either display. Here however I do not have two engines and two EMS modules.

Carl
 
Don't know the what kind of output the Dynon uses but this sounds like bad advice to me, typically tying audio outputs together is a no-no.
I'm pretty sure if you lose the PFD for some reason lost audio from it would be pretty low on the priority list.
On a Garmin system only the audio from the PFD gets routed to the audio panel.

Dynon's audio outputs have series resistors. The point of this is so that you can tie them together with other similar outputs without concern.

It also allows you to attenuate the audio levels by terminating with, say 50 ohm resistors to (audio) ground. This allows you to run the SV audio levels at a higher volume, which decrease the noise level.

The audio mixers I developed years ago all used series output resistors for similar reasons, and to prevent damage if shorted to ground, but also to allow expansion (could build a 20 channel mixer by connecting two 10 channel mixers together).

A lot of functionality for a mere resistor!
 
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