XLR audio pad attenuator

[frenchie29]

I need to build dome audio pads with XLR connectors

I found that
http://www.uneeda-audio.com/pads/

I think the top right one would apply to an XLR connector.

1----------------1
2---300ohm------2
|
4ohm
|
3---300ohm-----3


Would that give me a -30db attenuation?

I get the wiring but not sure how to come up with the right value for the resistors.