Thoughts on the most difficult instruments for speakers to reproduce?

Violins. High notes. 

kdude661,121 posts04-23-2018 11:49pmPiano,Piano,and Piano.

When you have a system that gets all aspects of the Piano correct everything thing else will be there,with maybe the exception of the lwr Organ notes being totally realistic.

Kenny.

100% agree.  In building components, I spent a few years on how to get the piano right.  I wanted to not only hear the wood of the piano and the hammers hitting the strings but I also wanted to hear the length and thickness of the strings and the attack and the decay.  It was a long road but now at the end, it was worth the effort.  Happy Listening.

Digital recordings are a terrible weakness of my system. Far too stucotto.

The obvious/tried-and-tested options are all mentioned above (ie, piano; massed strings; muted trumpet). 

But another instrument that tests speakers/entire system in a very different way is the vibraphone ("vibes"). This is primarily played in acoustic jazz and/or modern percussion composition.

The layout of brass keys is piano-like, but the sound is very different: keys are struck with mallets, so you get that 1st-strike transient, followed by lengthy sustain (courtesy of sound propagation tubes beneath each key). My favorite players use 2 mallets per hand & can play many notes, simultaneously or in fast sequence.

The result is a characteristic "shimmer" to the sound. It's a louder than you think, something microphones readily react to if not set up properly. 

I find that speakers & electronics that fully convey the complex sound of this instrument can generally hit it out of the park on just about every instrument.

Massed (not single) violins, I agree, and (surprised no one mentioned) full bodied, contrapuntal choral singing.