An "empty" bass clef in MuseScore has one thing in it: a whole rest.
This is what I'm going to show you how to make:
If you try to insert a quarter note in place of the whole rest, it will automatically get put into the first beat of the treble clef:
What we need is a half rest, followed by a quarter rest, followed by a quarter note.
So, select the whole rest:
Now click the "half note" button at the top and you'll get two half rests:
Now select the half rest on the right and click the "quarter note" button at the top and you'll now have a half rest and two quarter rests:
Now select the quarter rest on the right, press the "n" key to enter insert mode, then click, e.g. the B3 note position in the bass clef and you're done:
Download the MuseScore file ("save as" to somewhere on your computer, then open it in MuseScore)
Thanks to Nicolas Froment for this shortcut:
Just highlight the whole rest, then punch the following keys:
n 6 0 5 0 b
then ctrl+down-arrow to bring the B down an octave.
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