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Cisco audio Science ceiling Mic and SX20

Level 1
Level 1

  Hi Folks

We have a customer that has purchased a SX20 and also a Audio Science Ceiling Mic. I had a 3.5 "4 Pin Cable" made up to extend from the Codec, But when I plug in the Audio Science ceiling Mic , I cannot be heard.

Has anyone com across this issue ?

I have checked the pin outs ...all ok.

As a thought ...Are they compatible ?



21 Replies 21

Martin Koch
VIP Alumni
VIP Alumni

The C20/SX20 are not "integrator codecs".

I heard that some people got 3rd party mics to work, but I have never seen it myself and that will most likely

not be a supported deployment and TAC would most likely not help if you have trouble, so I would not recomend

going that way.

If you want to connect anything fancy, like external control panels, exend cables/connections, connect external audio systems / special microphones, ... use an integrator codec like C40/60/90.

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Hi Martin

Thanks for your advise...So I gather from all of that is that the SX20 Codec will NOT work with the Tandberg/Cisco Audio Science Ceiling Mic ???

If you are a sales guy:

Thats correct

If you are a tech guy:

Thats how I interpret it: even if you get it to work, you SHALL NOT (RFC2119) use it.

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Hi Rob,

we are using the SX20 with the Ceiling Mic. You have to provide provide power to the mic via connecting the mic control wirh a resistor to V+ on the XLR. I did not build the cable by myself, a audio equipment build it and we had the same issue. I think it's called phaentom power.

There is a similar topic, which was opened by a collegue before purchasing the cabile:

Regards, Paul

And this is exactly where I say, you shall not do that, as you might not know the consequences, like

draining to much power and frying the sx20 which then will most likely be rejected as an rma, ...

To get something to work does not always mean that its recommendable for others. ;-)

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Thanks for your Advise Martin..

Can we use the above mention circuit by using Resistors(680 Ohm) & capacitors (1 micro farad) for below mention requirement.


We are using SX10 codec & we need to use a balance line signal out from Biamp Nexia DSP as a Mic input to this codec. We are connecting 3 mics in Nexia DSP & mix Balance out will go to Mic In of SX10 codec for far end participants. 


The 4 pin connector pinout given by cisco is 1, 2, 3, 4 = T, R1, R2, S = Hot+, Cold-, Mic control, Ground respectively.


We are using 4 pin connector with the signal Hot+, Cold- , Ground as pins 1, 2, 4 respectively. We are not using pin 3 as Mic control for Mute/Unmute button. 

By using this connection we are not able to get audio at far end. 

Do we need to short pin 3 & 4 for grounding Mic control to work this?

If we use External Mic of Cisco, it works fine.

Please share the solution..

SX10 Mic In External Signal

Audio Signal is Tip & R1

Audio wont pass unless 100 R + 360 R resitors are connected between R2 & Sleeve

Paul, the link you provided to another thread does not mention a resistor between "Mic control" and "V+", but I might also add, the method on the other thread did not work for me, either.  Do you know the size of the resistor used in your cable?  Are you able to provide any wiring diagrams?


I'm very interested in this too - we have about 10 ceiling mics spare so I want to put them to use, even if it's not supported

Unfortunately not. The cable or adapter was build by company (3c vidision), which produces media systems.

Regards, Paul

Nick, any luck with external mics (which brand) and the SX20?????

Darren, Have you ever gotten this to work.  i am approaching a deadline and need to get some external mics/DSP integrated to the SX20.  I have had mixed results with your circuit.  The AT PRO45 worked while the Beyer Dynamics 33 did not...


Please help.



Peter, sorry for the late reply - yes, this is working for us, using the schematic I posted above.