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SX20 third party mics and Polycom soundstructure c-series


We are trying to connect a SX20 microphone port to the output of a Polycom soundstructure C12.
I'm wondering if anybody has been successful doing this?

It looks like the SX20 has to be tricked to believe its microphone is connected.
Maybe by sending some power on some pins?

I've seen several example on how to connect powered mics directly to the SX20 but the soundstructure output port is different and the codec keep the port shut when plugging it in.

Has anybody been able to connect a soundstructure or similar device to a SX20?




22 Replies 22


Could it be, that you´ve used a 3pin 3,5mm plug instead of the needed 4pin jack? This would shorten the mute pin on SX20.


We are using a 4pin 3.5mm and tried almost any wiring combination possible.

When looking at the volume meter under the SX20 admin settings, the volume bar goes dead as soon as you disconnect the SX20 included mic.

We haven't been able to get that volume bar up when plugging to the Soundstructure C12, so it looks like the SX20 does some mic detection test and we are failing it.

I've read somewhere that pin 2 and 3 had to be shorted to trick the SX20 to detect the mic but that didn't work for us.

We are running TC 7.2 .
What version are you running? 
I'm wondering if there is some mic detection code in that version that is tripping us.



I'm on 7.1.4

We are still seeing this issue in 7.2.1.

Do NOT use the volume bar status!  Go into the web browser and check audio input levels. There you will see your external miclevels.  Very confusing. Can't believe this is not more published!!!

Something else I just realized, why won't audio work with a disconnected mic? If there *is* code doing this, its very bad code. Just because someone unplugs a mic doesn't mean the audio output should be disabled.

The audio output of the codec is not disabled, only the mic port is.

What we are trying to do is connect third party ceiling mics.

The Ceiling mics are connected to the soundstructure C12 and the C12 output port connected to the SX20.

We have no issues with the audio output from the SX20.

OK, that clears it up. You said volume bar, so I thought you meant the main volume. :)

As a test, you  could try to connect a ceiling mic directly to the SX20 using an external phantom power supply or a dynamic microphone to see, if the issue is related to the soundstructure.


have you or anyone you know gotten any external mics to work with the sx20?

Were you able to get this working with the SoundStructure? We are doing something similar with a BiAmp, but to four SX20's.

We have wired the output to the four-position jack, and still get a warning about the mic not being detected.

Thanks in advance!

Aaron Wilson

I have connected ClearOne Interact systems to the SX20 with no ill effect. I'm using a male-3.5mm 3 conductor (SX20) to female RCA adapter (ClearOne). Even though its not a 4 conductor 3.5mm, it works just fine.

I do have some 4 conductor connectors, I just haven't soldiered them yet.


We finally got it to work by turning off HDMI audio.



when you say 'turning off HDMI audio' would this be on the input side?


We were only able to get this working with a third party microphone on V7.1.4 by connecting the Cisco microphone to enable microphone input and then using input 2 for the third party microphone.



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