jph@stephenson.net.dhis.org asked;

> I am looking for the specifications of the audio interface in the
> Personal DECstation 5000/20, such as required impedances etc. for
> the external speaker and microphone.
>
> Thanks in advance for all advices.
>
> Jean-Pierre

I consulted with Personal DECstation 5000 manual and DEC3000 
manual, and realized no specific details available besides pinout
diagram.    The RJ-11 port is known compatible with so-called "telephone
headset" (DEC sold such a gadget) and I believe it's OK to use dirt cheap
common headphone+microphone unit designed for telephone external.

facing to back, lead side up, from right to left
1    audio in
2    audio out
3    audio out return
4    audio in return (ground)

Toru Nishimura/ALKYL Technology