Not sure how to fit it into Pathfinder exactly (although it would of course need to be something to do with Bards), but many years ago I had this idea that I have never gotten to use:
Combat Bassoon: Designed to force enemy orchestras to surrender, this weapon had initially promising results, but was quickly withdrawn from service after logging an unacceptably high frequency of friendly fire incidents. However, it did lead to development of its baser cousin that actually saw some undercover service, the Iran Contrabassoon.
|Wow Such Doge|
|Wow Such Doge|
If you just want the appearance of an instrument, you could add the glamered enchantment to a weapon. Your dagger could look like a daggerish-flute, or your axe could look like the picture you linked to. At least until you attack with it.
Also, one of the powers that intelligent weapons can have is the ability to "change shape into one other form of the same size." The other form could be an instrument with a weapon-like appearance.
|Mirrel the Marvelous|
Mirrel the Marvelous wrote:Bagpipes! The only instrument to ever have been classed as a weapon of war!"12 highlanders and a bagpipe makes a rebellion." ~ Scottish Proverb
You have to admit: A violin in the wrong hands can be a deadly weapon . . . Just beware that this tends to make people want to start a rebellion against the user.
This is maybe not exactly what you're looking for, and especially not because of the price, but it does let you use a bow as a string instrument...
Actually pretty awesome for an archer Bard/Skald/etc., if you can manage to get your hands on one and then put it on a bow that has the other enchantments you want.
Behold, your Axe.
Now I've got this image of heavy metal rocker Bards/Skalds thrashing their enemies by whacking them with their guitars . . . .
Without magic, technology, or "its cool so F the physics" a stringed instrument that doesn't have a "box" section to amplify and tune the string will be too quiet for anyone to hear.
Mind you, the above is easy enough to get.
Though really, after remembering this stuff I find myself wanting to re-play Brutal Legend.
|Just a Guess|
The undine weapon shaft should make it easy to transform a weapon into a didgeridoo/flute/horn. Just needs to be open on both ends, that's all. But strings are harder because they are easily damaged in a fight.
What one player in a game I GM does is use a large flute in his offhand with the improvised defence trait to get a shield bonus while fighting unarmed.