Tangential connection to previous post: harps. I've played the harp for about 25 years now. I think that I chose it originally partly because of Welsh connections, but mostly just because I loved it. It's a wonderfully responsive instrument to play.
So when did the harp become so feminised? I should add straightaway that it isn't entirely feminised - many of the classical music world's most wonderful harpists are men (eg. Xavier de Maistre; Emmanuel Ceysson). And in Wales, where Henry V's interest in the harp may well have come from, there is little sense that this is a particularly female instrument.
I have just read an extremely interesting article by Hannah Lane (Cerae 1, 2014), which provides a rather convincing answer to this question. She discusses the introduction of the single-action mechanism in around 1720 (for harp nerds, these innovations are absolutely fascinating - harp-makers have always had to find solutions to enable the production of semi-tones on the harp, and the single-action pedal mechanism, succeeded by today's double-action pedal mechanism, is one solution). These new harps were more dynamically expressive, and the new chromatic possibilities led to a whole new repertoire which focused on the Empfindsamer style, which privileged emotional sensitivity. The single-action mechanism made possible, in particular, rapid or continuous arpeggiation - probably now the sound most associated with the classical harp and alternately tender or delicate, and stormy.
And this was a moment at which this kind of emotionalism was being more explicitly associated with femininity. To weep sweetly was women's work. An entry in Diderot's Encyclopedia in 1767 claimed that the single-action harp 'has become an object of amusement for the sensitive sex, who, far from depriving themselves of the emotions that the harp can excite in our souls by it sweet harmony and mellifluous sounds, lend to it even more favourable assistance in order to increase its charm' (Lane, p. 82). Emotional expression is clearly gendered in particular ways in particular periods, and to find that such labels might have shaped a long-standing perception of a musical instrument is very striking.
A concert grand pedal harp now holds about two tonnes of tension in the strings, and is capable of an enormous dynamic range. But throwing off the rather vapid 'feminine' associations is a slower process. The harp is not an instrument for lacy frocks, but powerful and expressive and as interesting and many-faced as we know gender to be.