How do you turn volume down on gdx intercom? It's too loud!

[missbuds]

Hi,
Can anyone please advise on how I can turn the volume down on my preinstalled gdx intercom? Its way too loud and I cannot have it on mute all the time.
I've seen similar posts but the pics of the internal board are slightly different and I seem unable to find the fix for it.
Thank you in advance for your help!

 

[Harry Bloomfield]

I think your only solution, may be - to add a suitable value of resistor, in series with the speaker.

 

[opps]

End of page 24 says

"The Audio Handset supports configurable volume control. This is adjusted by the administrator of the GDX system to limit disputes on noise levels."