I found an interesting series of videos from the Philharmonia in the U.K. posted on Youtube. One for each of the main orchestral instruments explained and demonstrated by a musician who plays them. It struck me that these would be a nice intro for would-be musicians trying to decide which instrument they would like to play.
Some of the musicians presented also explain how their instruments are typically employed in the orchestra and how different composers used them. I learned a few things I didn't know.
One thing that surprised me was that the double bass player said his bottom range was the low C and every orchestration book I had read said that the lowest note was E. The Philharmonia bass player showed a feature on his instrument that extended it to get the lowest notes. I had never seen, read, or heard of that before. I was wondering how common this is. Is it "safe" to write a bass part that goes into the extended range, or is that going to create problems for most bass players?
I have no idea about how common is the extension to C. The small local symphony orchestra I am in contact, has a double base player, and a good one, who has it on his beloved instrument and proudly demonstrated it to me. So, based on this, it is safe to compose for the double base C. This dedicated polish musician stays in my mind, because at one rehearsal his instrument fell over and developed a crack. He cried, but later I heard that he successfully got it repaired...
On another "note" I have often wondered about the low note on the oboe, Bb. I have read in orchestration books that this note is to be avoided, and even the B isn't all that great, making C the most reliable low note on the oboe. Any oboists here, or failing that, anyone with reliable experience in this? I am working on a piece and want to use that Bb. I also need to go one lower, but of course that's not an option, so I may give the A to the bassoon. The passage involves successive, detached notes in slow tempo, so the sudden switch to bassoon may work, especially as other things are going on, so it won't stand out too much. Plus, I am actually after the ducklike quality of the instrument, as the passage portrays seabirds.
Actually, the passage is on the Eng Horn. I wanted to double it for volume, and the oboe seemed the best candidate. although the Eng Horn doesn't seem to blend well with any other instrument. For now, I'm using a clarinet, as it it also a reed and thus has some of that barn-yard tang I'm after.
Piston points out that the Eng Horn blends well with muted trumpet, as evidence by Debussy’s use of this combo at the beginning of La Mer. but the trumpet, even muted, would be too much here.
Below D, the hautbois does become a bit thick and coarse, "honky" as oboe players sometimes put it. However, parts that dip down to C, B or Bb and get quickly away from them are not objectionable. The main point is to not stress these low notes in solo work. In ensemble the effect is not nearly as pronounced. These lower tones are sometimes used to achieve a special effect as in Stravinsky's Symphony of Psalms where they give an ultra-reedy, primitive flavor, and in Prokofieff's Peter and the Wolf where they are used to personify a duck.
If you are simply doubling the Cor Anglais, don't worry about it.
The Sonatina for wind instruments by Richard Strauss starts with a very exposed Bb on the oboe, don't be afraid to use it, if you have pro musicians.
Since about 1900 orchestral basses have an added 5th low C string. These basses are generally owned by the orchestra, at home bass players usually use a 4 strings 3/4 bass that goes down to E.
For solo work bass players use "solo tuning": F#, B, E, A.