There are two factors that are going to determine the total size of the orchestra or particular section we desire. The first is the loudness we want to achieve with a group of musicians and the second is the type of sound. The first is probably the most obvious: the more musicians we have, the louder the sound. The second is not so obvious. An increasing number of musicians will change the quality of the sound, and, at some point, the type of sound entirely. We can agree that adding more French horns to a solo French horn line would not only change the volume, but the sound of it as well. Similarly, a solo violin doesn’t sound like six violins playing in unison. So when balancing –and budgeting an orchestra– we will have to pay a great deal of attention to both.
In old school recording sessions (and still part of today’s recordings), as well as live performances, the main problem was only loudness: we want this particular brass/woodwind section to not overpower the string section (or in rare cases vice versa). In this situation, everybody is performing in the same room, so problems with a string section that becomes too thin would be uncommon.
But today’s recording sessions are often done in a way that every section, if not subsection, is recorded one after the other. This way, balance is not as important as long as all instruments in the room are balanced with each other. A mixing process afterwards can take care of re-balancing. However if due to budgetary concerns, the string section is reduced too far problems can occur. At some point the strings will sound thin or, in the worst case scenario, not even sound as a section but rather as a few soloists playing the same line. Limiting the number of string players also adds another problem: even the best violin/viola players have a hard time playing the same note when there are just three or four. So the end result will not only sound very soloist-ish and thin but also out of tune. Because of all these concerns , we recommend you reference the following “rule of thumb” chart in order to achieve the sound you want for every context.
Chart with section sizes: uploads/topics/size-and-balance-in-today-s-context-1-5933ffe9b1fd8.pdf
Considering the previous chart, and the fact that the larger the instrument is the louder it will sound, we can conclude that some ratios for a balanced string orchestra will be something like the following chart(4):
Chart with string sizes: uploads/topics/size-and-balance-in-today-s-context-2-5933ffefa891e.pdf
These number will also depend on how we want the orchestra to sound. We may want the violas to add that warmth to the overall sound or we may want it brighter. On the other hand we might want to have more low register supporting the rest of the strings. And again, the better the players are the better the orchestra will sound both in loudness and tuning.
The kind of sound we want will also determine the numbers of woodwinds and brass. As for the woodwinds, anything that should sound “soloist-ish” can go from the one woodwind we may want to a duo, trio, quartet or even sextet, in different combinations that we might need for the kind of music we are making. For example, it might be a piece or cue that requires a duet of flutes, an oboe, and a clarinet. Another may ask for an alto flute, an english horn, and a pair of clarinets and bassoons. Then, for a more symphonic woodwind section sound, we can start with a section in a2, expand it with an a3, up to the rare section of a4 or more.
The brass is slightly different to the woodwinds; they play in unison more often than the woodwind section, so it is not rare to see 2, 4, 6, 8, or even 12 horns playing in unison. And as we see and hear in Mahler symphonies, as soon as the numbers go up in one subsection of the brass we need to raise them in the rest of the subsections. The sound of the French horn section will obviously change its quality going from the pure and mellow sound of a single horn through to the continuously less pure sounding shades of 2, 4, 6 or 8 horns where the sound gets considerably thicker, and more powerful and brassy when they play in forte. The numbers of the trumpets are similar but divided by two, so they go from two trumpets in unison to 3, 4, up to 6. The low brass section doesn’t usually change much from the standard trio of two tenor trombones and a bass trombone or 2/3 tenors and cimbasso, plus a tuba as the foundation.
So, if we put together the numbers of the different sections, we will come up with the following chart for the whole orchestra: