DM crossword - just checking

[Jock13]

Have answered this, but can't fully fit it to the clue.
Clue is; Speed of sound primarily shows men off showing this?
I think it's MACHISMO - MACH - speed of sound - but can't see where the rest comes from. Could anyone reassure me, please?

[cancross]

Looks good, the "I" is a bit tricky but primarily shows men off is S M O

[kettledrum]

mach 1 = speed of sound + S(hows) M(en) O(ff)

[gen2]

Primarily suggests looking at the first letters

primarily Shows Men Off = SMO

Speed of sound = Mach 1 = MACHI

[Jock13]

Great! Thanks very much for all three replies - a case of easy when you know how - now I can relax - thanks again.