From Academic Kids
The heckelphone is a musical instrument invented by Wilhelm Heckel and introduced in the late 19th century. It is a double reed instrument of the oboe family, but with a wider bore and hence a heavier and more penetrating tone. It is pitched an octave below the regular oboe and furnished with an additional semitone taking its range down to A (though Richard Strauss writes for it as low as an impossible F), and in the repertoire it is almost invariably used as the bass of an oboe section incorporating the regular oboe and the cor anglais.
The first significant use of the heckelphone was in Strauss's 1905 opera Salome, and the instrument was subsequently employed in the same composer's Elektra and Eine Alpensinfonie. It enjoyed some vogue among English composers of the early 20th century, being used in Gustav Holst's famous orchestral suite The Planets (1916), as well as several works of Delius (A Mass of Life, Dance Rhapsody No. 1, etc.), Bax's Symphony No. 1, and Havergal Brian's Symphony No.1 (The Gothic) and Symphony No. 4 (Das Siegeslied). In the usage of English composers, the heckelphone is generally referred to by the name bass oboe, which, though descriptive, invites confusion with the somewhat different earlier instrument of the same or similar name (French hautbois baryton). In some cases, it is possible that the composers themselves were unclear as to the distinction between the two instruments.
For all its potential in adding weight to the lower registers of the woodwind section, the heckelphone remains a rarity on the orchestral scene, and is seldom carried on the regular strength of professional orchestras.