Prism III is the third of five albums in which the Danish String Quartet place one of Beethoven's late quartets between a Bach fugue and a later work that grew out of it. Here the line runs from Johann Sebastian Bach's Fugue in C-sharp minor, BWV 849, through Ludwig van Beethoven's String Quartet No. 14, Op. 131, to Béla Bartók's String Quartet No. 1. In the quartet's own image, Beethoven took Bach's linear writing and "exploded everything into myriads of different colours", the way a prism splits light.

The players are Frederik Øland and Rune Tonsgaard Sørensen (violins), Asbjørn Nørgaard (viola) and Fredrik Schøyen Sjölin (cello). They recorded the programme in November 2017 at the Reitstadel in Neumarkt, a former riding hall, with Markus Heiland as engineer and Manfred Eicher producing. The Bach fugue is heard in the string quartet arrangement by Emanuel Aloys Förster, a Viennese composer of Beethoven's time, and Paul Griffiths wrote the liner notes. The first two volumes had paired Beethoven with quartets by Shostakovich and Schnittke.

Op. 131 dates from 1826 and runs through seven sections without a pause, opening with a slow fugue in the same key as the Bach. Its centre is the set of variations marked Andante ma non troppo e molto, almost fifteen minutes long here, followed by a quicksilver Presto. Bartók's First Quartet, completed in 1909, begins with a lamenting Lento built on imitative lines that answer Beethoven's opening, and ends in a rough, folk-coloured Allegro vivace. Placing the Bach last turns it into a quiet postlude, and Gramophone's Peter Quantrill heard it as handing back "the melodic key to Op 131".

Reviewers were struck by the sound of the hall as much as the playing. Writing in The Strad in 2021, David Kettle admitted the disc "doesn't make for easy listening but it's thrillingly daring". On AllMusic, James Manheim heard the same mix of counterpoint and folk material linking Beethoven to Bartók. He called the disc "an intriguing Beethoven release that is both expertly executed and worthy of discussion". The series went on to two further volumes, closing in 2023.

CD edition, ECM New Series 2563, first released in March 2021, with a booklet of notes in English and German.