Image Search: Music Tuner. “A Rough Guide to Compact Stage Tuners”. Performing-Musician.com. 21.03.2016
Most musicians are aware that concert pitch has risen in recent years, with current practice more or less around 440+ Hz. They may not know, however, that from the beginning of modern orchestras (circa 1670) concert pitch rose from 392 Hz to a high of 452 Hz by the end of the 19th century. Things were reset by international convention in 1939, back to 440 Hz where it more or less remains, albeit straining to rise yet again. The question is: Why does this happen? Jeremy Montagu (1) provides us a convincing analysis. Simplifying his argument: Larger middle-class public audiences meant Larger concert venues demanding increased instrumental forces to supply sufficient sound/audibility. At the limit of this spiralling process (how big can a concert venue get, and how can you pay for more than around 100 musicians and still make a profit???), the only way to increase audibility was to modify instruments, to wit by increasing pitch. Increased pitch ipso facto increased sound and brilliance. And that, dear readers, is what is still going on. (Otherwise we must resort to electric amplification, which not coincidentally is happening in parallel!).
1. Montagu, Jeremy. Origins and Development of Musical Instruments. London: Scarecrow Press, 2007. Page 117.