I recently listened to Horațiu Rădulescu’s streichquartett nr. 4 opus 33 performed by the Arditti quartet. The vast spectral sound-world of 128 strings is striking and quasi-fantastical.
About Horațiu Rădulescu: Roman-French composer Horațiu Rădulescu frequently employed spectral techniques in his compositions. His sound-worlds are described as ‘cosmic’, ‘strange’ and ‘archaic’. Oliver Messiaen described Rădulescu as a composer who ‘contributed to the renewal of musical language’. 
About streichquartett nr. 4 opus 33: This piece is composed for nine spatialised string quartets. A central live string quartet surrounded by an audience who are, in turn, surrounded by eight string quartets which, according to Rădulescu, can be live or pre-recorded. 
Of streichquartett nr. 4 opus 33, Rădulescu writes:
The title is an answer to Shakespeare’s “to be or not to be” and to Lao-tzu’s “being and non-being create each other”. The idea of this opus initially came in the Loire Valley near the Clos Luce where Leonardo spent his last years: a central string quartet […] surrounded by the enormous circle of an imaginary “viola da gamba” with 128 strings… 
The concept of time is particularly interesting in this piece. The time-worlds of the central live string quartet and the surrounding fantastical viola da gamba overlap. However, more interesting yet is the traditional-temporal implications of the ensemble. I personally find it thought-provoking how his streichquartett nr. 4 opus 33 denies the tempered scale by formulating a spectral scale of unequal intervals. To me, this notion is quasi-paradoxical because the string quartet is an ensemble of strings all of which are tuned according to the tempered scale. However, this is one of the reasons why I like the piece: the string quartet invariably involves historical implications for any composer, and Rădulescu’s music seems to attempt to overcome this with a curious cosmic sound-world of interwoven textures, ‘spectral fingering and bowing techniques’. Whether he does succeed in overcoming this is probably a matter of opinion: it will always be a connected with the string-quartet genre because it is written for string quartet; however, the encounter I have with this piece feels somewhat removed from the type of encounter I have with classical string quartet music.